892 lines
22 KiB
C
892 lines
22 KiB
C
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// SPDX-License-Identifier: GPL-2.0
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/*
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* trace_hwlat.c - A simple Hardware Latency detector.
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*
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* Use this tracer to detect large system latencies induced by the behavior of
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* certain underlying system hardware or firmware, independent of Linux itself.
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* The code was developed originally to detect the presence of SMIs on Intel
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* and AMD systems, although there is no dependency upon x86 herein.
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*
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* The classical example usage of this tracer is in detecting the presence of
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* SMIs or System Management Interrupts on Intel and AMD systems. An SMI is a
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* somewhat special form of hardware interrupt spawned from earlier CPU debug
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* modes in which the (BIOS/EFI/etc.) firmware arranges for the South Bridge
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* LPC (or other device) to generate a special interrupt under certain
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* circumstances, for example, upon expiration of a special SMI timer device,
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* due to certain external thermal readings, on certain I/O address accesses,
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* and other situations. An SMI hits a special CPU pin, triggers a special
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* SMI mode (complete with special memory map), and the OS is unaware.
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*
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* Although certain hardware-inducing latencies are necessary (for example,
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* a modern system often requires an SMI handler for correct thermal control
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* and remote management) they can wreak havoc upon any OS-level performance
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* guarantees toward low-latency, especially when the OS is not even made
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* aware of the presence of these interrupts. For this reason, we need a
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* somewhat brute force mechanism to detect these interrupts. In this case,
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* we do it by hogging all of the CPU(s) for configurable timer intervals,
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* sampling the built-in CPU timer, looking for discontiguous readings.
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*
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* WARNING: This implementation necessarily introduces latencies. Therefore,
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* you should NEVER use this tracer while running in a production
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* environment requiring any kind of low-latency performance
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* guarantee(s).
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*
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* Copyright (C) 2008-2009 Jon Masters, Red Hat, Inc. <jcm@redhat.com>
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* Copyright (C) 2013-2016 Steven Rostedt, Red Hat, Inc. <srostedt@redhat.com>
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*
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* Includes useful feedback from Clark Williams <williams@redhat.com>
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*
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*/
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#include <linux/kthread.h>
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#include <linux/tracefs.h>
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#include <linux/uaccess.h>
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#include <linux/cpumask.h>
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#include <linux/delay.h>
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#include <linux/sched/clock.h>
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#include "trace.h"
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static struct trace_array *hwlat_trace;
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#define U64STR_SIZE 22 /* 20 digits max */
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#define BANNER "hwlat_detector: "
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#define DEFAULT_SAMPLE_WINDOW 1000000 /* 1s */
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#define DEFAULT_SAMPLE_WIDTH 500000 /* 0.5s */
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#define DEFAULT_LAT_THRESHOLD 10 /* 10us */
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static struct dentry *hwlat_sample_width; /* sample width us */
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static struct dentry *hwlat_sample_window; /* sample window us */
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static struct dentry *hwlat_thread_mode; /* hwlat thread mode */
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enum {
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MODE_NONE = 0,
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MODE_ROUND_ROBIN,
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MODE_PER_CPU,
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MODE_MAX
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};
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static char *thread_mode_str[] = { "none", "round-robin", "per-cpu" };
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/* Save the previous tracing_thresh value */
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static unsigned long save_tracing_thresh;
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/* runtime kthread data */
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struct hwlat_kthread_data {
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struct task_struct *kthread;
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/* NMI timestamp counters */
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u64 nmi_ts_start;
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u64 nmi_total_ts;
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int nmi_count;
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int nmi_cpu;
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};
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static struct hwlat_kthread_data hwlat_single_cpu_data;
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static DEFINE_PER_CPU(struct hwlat_kthread_data, hwlat_per_cpu_data);
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/* Tells NMIs to call back to the hwlat tracer to record timestamps */
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bool trace_hwlat_callback_enabled;
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/* If the user changed threshold, remember it */
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static u64 last_tracing_thresh = DEFAULT_LAT_THRESHOLD * NSEC_PER_USEC;
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/* Individual latency samples are stored here when detected. */
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struct hwlat_sample {
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u64 seqnum; /* unique sequence */
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u64 duration; /* delta */
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u64 outer_duration; /* delta (outer loop) */
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u64 nmi_total_ts; /* Total time spent in NMIs */
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struct timespec64 timestamp; /* wall time */
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int nmi_count; /* # NMIs during this sample */
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int count; /* # of iterations over thresh */
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};
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/* keep the global state somewhere. */
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static struct hwlat_data {
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struct mutex lock; /* protect changes */
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u64 count; /* total since reset */
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u64 sample_window; /* total sampling window (on+off) */
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u64 sample_width; /* active sampling portion of window */
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int thread_mode; /* thread mode */
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} hwlat_data = {
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.sample_window = DEFAULT_SAMPLE_WINDOW,
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.sample_width = DEFAULT_SAMPLE_WIDTH,
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.thread_mode = MODE_ROUND_ROBIN
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};
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static struct hwlat_kthread_data *get_cpu_data(void)
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{
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if (hwlat_data.thread_mode == MODE_PER_CPU)
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return this_cpu_ptr(&hwlat_per_cpu_data);
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else
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return &hwlat_single_cpu_data;
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}
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static bool hwlat_busy;
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static void trace_hwlat_sample(struct hwlat_sample *sample)
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{
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struct trace_array *tr = hwlat_trace;
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struct trace_event_call *call = &event_hwlat;
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struct trace_buffer *buffer = tr->array_buffer.buffer;
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struct ring_buffer_event *event;
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struct hwlat_entry *entry;
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event = trace_buffer_lock_reserve(buffer, TRACE_HWLAT, sizeof(*entry),
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tracing_gen_ctx());
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if (!event)
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return;
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entry = ring_buffer_event_data(event);
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entry->seqnum = sample->seqnum;
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entry->duration = sample->duration;
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entry->outer_duration = sample->outer_duration;
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entry->timestamp = sample->timestamp;
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entry->nmi_total_ts = sample->nmi_total_ts;
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entry->nmi_count = sample->nmi_count;
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entry->count = sample->count;
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if (!call_filter_check_discard(call, entry, buffer, event))
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trace_buffer_unlock_commit_nostack(buffer, event);
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}
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/* Macros to encapsulate the time capturing infrastructure */
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#define time_type u64
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#define time_get() trace_clock_local()
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#define time_to_us(x) div_u64(x, 1000)
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#define time_sub(a, b) ((a) - (b))
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#define init_time(a, b) (a = b)
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#define time_u64(a) a
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void trace_hwlat_callback(bool enter)
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{
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struct hwlat_kthread_data *kdata = get_cpu_data();
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if (!kdata->kthread)
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return;
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/*
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* Currently trace_clock_local() calls sched_clock() and the
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* generic version is not NMI safe.
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*/
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if (!IS_ENABLED(CONFIG_GENERIC_SCHED_CLOCK)) {
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if (enter)
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kdata->nmi_ts_start = time_get();
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else
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kdata->nmi_total_ts += time_get() - kdata->nmi_ts_start;
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}
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if (enter)
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kdata->nmi_count++;
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}
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/*
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* hwlat_err - report a hwlat error.
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*/
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#define hwlat_err(msg) ({ \
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struct trace_array *tr = hwlat_trace; \
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\
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trace_array_printk_buf(tr->array_buffer.buffer, _THIS_IP_, msg); \
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})
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/**
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* get_sample - sample the CPU TSC and look for likely hardware latencies
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*
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* Used to repeatedly capture the CPU TSC (or similar), looking for potential
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* hardware-induced latency. Called with interrupts disabled and with
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* hwlat_data.lock held.
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*/
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static int get_sample(void)
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{
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struct hwlat_kthread_data *kdata = get_cpu_data();
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struct trace_array *tr = hwlat_trace;
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struct hwlat_sample s;
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time_type start, t1, t2, last_t2;
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s64 diff, outer_diff, total, last_total = 0;
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u64 sample = 0;
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u64 thresh = tracing_thresh;
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u64 outer_sample = 0;
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int ret = -1;
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unsigned int count = 0;
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do_div(thresh, NSEC_PER_USEC); /* modifies interval value */
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kdata->nmi_total_ts = 0;
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kdata->nmi_count = 0;
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/* Make sure NMIs see this first */
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barrier();
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trace_hwlat_callback_enabled = true;
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init_time(last_t2, 0);
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start = time_get(); /* start timestamp */
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outer_diff = 0;
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do {
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t1 = time_get(); /* we'll look for a discontinuity */
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t2 = time_get();
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if (time_u64(last_t2)) {
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/* Check the delta from outer loop (t2 to next t1) */
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outer_diff = time_to_us(time_sub(t1, last_t2));
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/* This shouldn't happen */
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if (outer_diff < 0) {
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hwlat_err(BANNER "time running backwards\n");
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goto out;
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}
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if (outer_diff > outer_sample)
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outer_sample = outer_diff;
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}
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last_t2 = t2;
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total = time_to_us(time_sub(t2, start)); /* sample width */
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/* Check for possible overflows */
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if (total < last_total) {
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hwlat_err("Time total overflowed\n");
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break;
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}
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last_total = total;
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/* This checks the inner loop (t1 to t2) */
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diff = time_to_us(time_sub(t2, t1)); /* current diff */
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if (diff > thresh || outer_diff > thresh) {
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if (!count)
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ktime_get_real_ts64(&s.timestamp);
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count++;
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}
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/* This shouldn't happen */
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if (diff < 0) {
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hwlat_err(BANNER "time running backwards\n");
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goto out;
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}
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if (diff > sample)
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sample = diff; /* only want highest value */
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} while (total <= hwlat_data.sample_width);
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barrier(); /* finish the above in the view for NMIs */
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trace_hwlat_callback_enabled = false;
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barrier(); /* Make sure nmi_total_ts is no longer updated */
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ret = 0;
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/* If we exceed the threshold value, we have found a hardware latency */
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if (sample > thresh || outer_sample > thresh) {
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u64 latency;
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ret = 1;
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/* We read in microseconds */
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if (kdata->nmi_total_ts)
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do_div(kdata->nmi_total_ts, NSEC_PER_USEC);
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hwlat_data.count++;
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s.seqnum = hwlat_data.count;
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s.duration = sample;
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s.outer_duration = outer_sample;
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s.nmi_total_ts = kdata->nmi_total_ts;
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s.nmi_count = kdata->nmi_count;
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s.count = count;
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trace_hwlat_sample(&s);
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latency = max(sample, outer_sample);
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/* Keep a running maximum ever recorded hardware latency */
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if (latency > tr->max_latency) {
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tr->max_latency = latency;
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latency_fsnotify(tr);
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}
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}
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out:
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return ret;
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}
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static struct cpumask save_cpumask;
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static void move_to_next_cpu(void)
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{
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struct cpumask *current_mask = &save_cpumask;
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struct trace_array *tr = hwlat_trace;
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int next_cpu;
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/*
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* If for some reason the user modifies the CPU affinity
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* of this thread, then stop migrating for the duration
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* of the current test.
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*/
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if (!cpumask_equal(current_mask, current->cpus_ptr))
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goto change_mode;
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cpus_read_lock();
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cpumask_and(current_mask, cpu_online_mask, tr->tracing_cpumask);
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next_cpu = cpumask_next(raw_smp_processor_id(), current_mask);
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cpus_read_unlock();
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if (next_cpu >= nr_cpu_ids)
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next_cpu = cpumask_first(current_mask);
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if (next_cpu >= nr_cpu_ids) /* Shouldn't happen! */
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goto change_mode;
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cpumask_clear(current_mask);
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cpumask_set_cpu(next_cpu, current_mask);
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set_cpus_allowed_ptr(current, current_mask);
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return;
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change_mode:
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hwlat_data.thread_mode = MODE_NONE;
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pr_info(BANNER "cpumask changed while in round-robin mode, switching to mode none\n");
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}
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/*
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* kthread_fn - The CPU time sampling/hardware latency detection kernel thread
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*
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* Used to periodically sample the CPU TSC via a call to get_sample. We
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* disable interrupts, which does (intentionally) introduce latency since we
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* need to ensure nothing else might be running (and thus preempting).
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* Obviously this should never be used in production environments.
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*
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* Executes one loop interaction on each CPU in tracing_cpumask sysfs file.
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*/
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static int kthread_fn(void *data)
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{
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u64 interval;
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while (!kthread_should_stop()) {
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if (hwlat_data.thread_mode == MODE_ROUND_ROBIN)
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move_to_next_cpu();
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local_irq_disable();
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get_sample();
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local_irq_enable();
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mutex_lock(&hwlat_data.lock);
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interval = hwlat_data.sample_window - hwlat_data.sample_width;
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mutex_unlock(&hwlat_data.lock);
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do_div(interval, USEC_PER_MSEC); /* modifies interval value */
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/* Always sleep for at least 1ms */
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if (interval < 1)
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interval = 1;
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if (msleep_interruptible(interval))
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break;
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}
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return 0;
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}
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/*
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* stop_stop_kthread - Inform the hardware latency sampling/detector kthread to stop
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*
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* This kicks the running hardware latency sampling/detector kernel thread and
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* tells it to stop sampling now. Use this on unload and at system shutdown.
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*/
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static void stop_single_kthread(void)
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{
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struct hwlat_kthread_data *kdata = get_cpu_data();
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struct task_struct *kthread;
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cpus_read_lock();
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kthread = kdata->kthread;
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if (!kthread)
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goto out_put_cpus;
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kthread_stop(kthread);
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kdata->kthread = NULL;
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out_put_cpus:
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cpus_read_unlock();
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}
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/*
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* start_single_kthread - Kick off the hardware latency sampling/detector kthread
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*
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* This starts the kernel thread that will sit and sample the CPU timestamp
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* counter (TSC or similar) and look for potential hardware latencies.
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*/
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static int start_single_kthread(struct trace_array *tr)
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{
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struct hwlat_kthread_data *kdata = get_cpu_data();
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struct cpumask *current_mask = &save_cpumask;
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struct task_struct *kthread;
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int next_cpu;
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cpus_read_lock();
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if (kdata->kthread)
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goto out_put_cpus;
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kthread = kthread_create(kthread_fn, NULL, "hwlatd");
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if (IS_ERR(kthread)) {
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pr_err(BANNER "could not start sampling thread\n");
|
||
|
cpus_read_unlock();
|
||
|
return -ENOMEM;
|
||
|
}
|
||
|
|
||
|
/* Just pick the first CPU on first iteration */
|
||
|
cpumask_and(current_mask, cpu_online_mask, tr->tracing_cpumask);
|
||
|
|
||
|
if (hwlat_data.thread_mode == MODE_ROUND_ROBIN) {
|
||
|
next_cpu = cpumask_first(current_mask);
|
||
|
cpumask_clear(current_mask);
|
||
|
cpumask_set_cpu(next_cpu, current_mask);
|
||
|
|
||
|
}
|
||
|
|
||
|
set_cpus_allowed_ptr(kthread, current_mask);
|
||
|
|
||
|
kdata->kthread = kthread;
|
||
|
wake_up_process(kthread);
|
||
|
|
||
|
out_put_cpus:
|
||
|
cpus_read_unlock();
|
||
|
return 0;
|
||
|
}
|
||
|
|
||
|
/*
|
||
|
* stop_cpu_kthread - Stop a hwlat cpu kthread
|
||
|
*/
|
||
|
static void stop_cpu_kthread(unsigned int cpu)
|
||
|
{
|
||
|
struct task_struct *kthread;
|
||
|
|
||
|
kthread = per_cpu(hwlat_per_cpu_data, cpu).kthread;
|
||
|
if (kthread)
|
||
|
kthread_stop(kthread);
|
||
|
per_cpu(hwlat_per_cpu_data, cpu).kthread = NULL;
|
||
|
}
|
||
|
|
||
|
/*
|
||
|
* stop_per_cpu_kthreads - Inform the hardware latency sampling/detector kthread to stop
|
||
|
*
|
||
|
* This kicks the running hardware latency sampling/detector kernel threads and
|
||
|
* tells it to stop sampling now. Use this on unload and at system shutdown.
|
||
|
*/
|
||
|
static void stop_per_cpu_kthreads(void)
|
||
|
{
|
||
|
unsigned int cpu;
|
||
|
|
||
|
cpus_read_lock();
|
||
|
for_each_online_cpu(cpu)
|
||
|
stop_cpu_kthread(cpu);
|
||
|
cpus_read_unlock();
|
||
|
}
|
||
|
|
||
|
/*
|
||
|
* start_cpu_kthread - Start a hwlat cpu kthread
|
||
|
*/
|
||
|
static int start_cpu_kthread(unsigned int cpu)
|
||
|
{
|
||
|
struct task_struct *kthread;
|
||
|
|
||
|
/* Do not start a new hwlatd thread if it is already running */
|
||
|
if (per_cpu(hwlat_per_cpu_data, cpu).kthread)
|
||
|
return 0;
|
||
|
|
||
|
kthread = kthread_run_on_cpu(kthread_fn, NULL, cpu, "hwlatd/%u");
|
||
|
if (IS_ERR(kthread)) {
|
||
|
pr_err(BANNER "could not start sampling thread\n");
|
||
|
return -ENOMEM;
|
||
|
}
|
||
|
|
||
|
per_cpu(hwlat_per_cpu_data, cpu).kthread = kthread;
|
||
|
|
||
|
return 0;
|
||
|
}
|
||
|
|
||
|
#ifdef CONFIG_HOTPLUG_CPU
|
||
|
static void hwlat_hotplug_workfn(struct work_struct *dummy)
|
||
|
{
|
||
|
struct trace_array *tr = hwlat_trace;
|
||
|
unsigned int cpu = smp_processor_id();
|
||
|
|
||
|
mutex_lock(&trace_types_lock);
|
||
|
mutex_lock(&hwlat_data.lock);
|
||
|
cpus_read_lock();
|
||
|
|
||
|
if (!hwlat_busy || hwlat_data.thread_mode != MODE_PER_CPU)
|
||
|
goto out_unlock;
|
||
|
|
||
|
if (!cpumask_test_cpu(cpu, tr->tracing_cpumask))
|
||
|
goto out_unlock;
|
||
|
|
||
|
start_cpu_kthread(cpu);
|
||
|
|
||
|
out_unlock:
|
||
|
cpus_read_unlock();
|
||
|
mutex_unlock(&hwlat_data.lock);
|
||
|
mutex_unlock(&trace_types_lock);
|
||
|
}
|
||
|
|
||
|
static DECLARE_WORK(hwlat_hotplug_work, hwlat_hotplug_workfn);
|
||
|
|
||
|
/*
|
||
|
* hwlat_cpu_init - CPU hotplug online callback function
|
||
|
*/
|
||
|
static int hwlat_cpu_init(unsigned int cpu)
|
||
|
{
|
||
|
schedule_work_on(cpu, &hwlat_hotplug_work);
|
||
|
return 0;
|
||
|
}
|
||
|
|
||
|
/*
|
||
|
* hwlat_cpu_die - CPU hotplug offline callback function
|
||
|
*/
|
||
|
static int hwlat_cpu_die(unsigned int cpu)
|
||
|
{
|
||
|
stop_cpu_kthread(cpu);
|
||
|
return 0;
|
||
|
}
|
||
|
|
||
|
static void hwlat_init_hotplug_support(void)
|
||
|
{
|
||
|
int ret;
|
||
|
|
||
|
ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "trace/hwlat:online",
|
||
|
hwlat_cpu_init, hwlat_cpu_die);
|
||
|
if (ret < 0)
|
||
|
pr_warn(BANNER "Error to init cpu hotplug support\n");
|
||
|
|
||
|
return;
|
||
|
}
|
||
|
#else /* CONFIG_HOTPLUG_CPU */
|
||
|
static void hwlat_init_hotplug_support(void)
|
||
|
{
|
||
|
return;
|
||
|
}
|
||
|
#endif /* CONFIG_HOTPLUG_CPU */
|
||
|
|
||
|
/*
|
||
|
* start_per_cpu_kthreads - Kick off the hardware latency sampling/detector kthreads
|
||
|
*
|
||
|
* This starts the kernel threads that will sit on potentially all cpus and
|
||
|
* sample the CPU timestamp counter (TSC or similar) and look for potential
|
||
|
* hardware latencies.
|
||
|
*/
|
||
|
static int start_per_cpu_kthreads(struct trace_array *tr)
|
||
|
{
|
||
|
struct cpumask *current_mask = &save_cpumask;
|
||
|
unsigned int cpu;
|
||
|
int retval;
|
||
|
|
||
|
cpus_read_lock();
|
||
|
/*
|
||
|
* Run only on CPUs in which hwlat is allowed to run.
|
||
|
*/
|
||
|
cpumask_and(current_mask, cpu_online_mask, tr->tracing_cpumask);
|
||
|
|
||
|
for_each_cpu(cpu, current_mask) {
|
||
|
retval = start_cpu_kthread(cpu);
|
||
|
if (retval)
|
||
|
goto out_error;
|
||
|
}
|
||
|
cpus_read_unlock();
|
||
|
|
||
|
return 0;
|
||
|
|
||
|
out_error:
|
||
|
cpus_read_unlock();
|
||
|
stop_per_cpu_kthreads();
|
||
|
return retval;
|
||
|
}
|
||
|
|
||
|
static void *s_mode_start(struct seq_file *s, loff_t *pos)
|
||
|
{
|
||
|
int mode = *pos;
|
||
|
|
||
|
mutex_lock(&hwlat_data.lock);
|
||
|
|
||
|
if (mode >= MODE_MAX)
|
||
|
return NULL;
|
||
|
|
||
|
return pos;
|
||
|
}
|
||
|
|
||
|
static void *s_mode_next(struct seq_file *s, void *v, loff_t *pos)
|
||
|
{
|
||
|
int mode = ++(*pos);
|
||
|
|
||
|
if (mode >= MODE_MAX)
|
||
|
return NULL;
|
||
|
|
||
|
return pos;
|
||
|
}
|
||
|
|
||
|
static int s_mode_show(struct seq_file *s, void *v)
|
||
|
{
|
||
|
loff_t *pos = v;
|
||
|
int mode = *pos;
|
||
|
|
||
|
if (mode == hwlat_data.thread_mode)
|
||
|
seq_printf(s, "[%s]", thread_mode_str[mode]);
|
||
|
else
|
||
|
seq_printf(s, "%s", thread_mode_str[mode]);
|
||
|
|
||
|
if (mode < MODE_MAX - 1) /* if mode is any but last */
|
||
|
seq_puts(s, " ");
|
||
|
|
||
|
return 0;
|
||
|
}
|
||
|
|
||
|
static void s_mode_stop(struct seq_file *s, void *v)
|
||
|
{
|
||
|
seq_puts(s, "\n");
|
||
|
mutex_unlock(&hwlat_data.lock);
|
||
|
}
|
||
|
|
||
|
static const struct seq_operations thread_mode_seq_ops = {
|
||
|
.start = s_mode_start,
|
||
|
.next = s_mode_next,
|
||
|
.show = s_mode_show,
|
||
|
.stop = s_mode_stop
|
||
|
};
|
||
|
|
||
|
static int hwlat_mode_open(struct inode *inode, struct file *file)
|
||
|
{
|
||
|
return seq_open(file, &thread_mode_seq_ops);
|
||
|
};
|
||
|
|
||
|
static void hwlat_tracer_start(struct trace_array *tr);
|
||
|
static void hwlat_tracer_stop(struct trace_array *tr);
|
||
|
|
||
|
/**
|
||
|
* hwlat_mode_write - Write function for "mode" entry
|
||
|
* @filp: The active open file structure
|
||
|
* @ubuf: The user buffer that contains the value to write
|
||
|
* @cnt: The maximum number of bytes to write to "file"
|
||
|
* @ppos: The current position in @file
|
||
|
*
|
||
|
* This function provides a write implementation for the "mode" interface
|
||
|
* to the hardware latency detector. hwlatd has different operation modes.
|
||
|
* The "none" sets the allowed cpumask for a single hwlatd thread at the
|
||
|
* startup and lets the scheduler handle the migration. The default mode is
|
||
|
* the "round-robin" one, in which a single hwlatd thread runs, migrating
|
||
|
* among the allowed CPUs in a round-robin fashion. The "per-cpu" mode
|
||
|
* creates one hwlatd thread per allowed CPU.
|
||
|
*/
|
||
|
static ssize_t hwlat_mode_write(struct file *filp, const char __user *ubuf,
|
||
|
size_t cnt, loff_t *ppos)
|
||
|
{
|
||
|
struct trace_array *tr = hwlat_trace;
|
||
|
const char *mode;
|
||
|
char buf[64];
|
||
|
int ret, i;
|
||
|
|
||
|
if (cnt >= sizeof(buf))
|
||
|
return -EINVAL;
|
||
|
|
||
|
if (copy_from_user(buf, ubuf, cnt))
|
||
|
return -EFAULT;
|
||
|
|
||
|
buf[cnt] = 0;
|
||
|
|
||
|
mode = strstrip(buf);
|
||
|
|
||
|
ret = -EINVAL;
|
||
|
|
||
|
/*
|
||
|
* trace_types_lock is taken to avoid concurrency on start/stop
|
||
|
* and hwlat_busy.
|
||
|
*/
|
||
|
mutex_lock(&trace_types_lock);
|
||
|
if (hwlat_busy)
|
||
|
hwlat_tracer_stop(tr);
|
||
|
|
||
|
mutex_lock(&hwlat_data.lock);
|
||
|
|
||
|
for (i = 0; i < MODE_MAX; i++) {
|
||
|
if (strcmp(mode, thread_mode_str[i]) == 0) {
|
||
|
hwlat_data.thread_mode = i;
|
||
|
ret = cnt;
|
||
|
}
|
||
|
}
|
||
|
|
||
|
mutex_unlock(&hwlat_data.lock);
|
||
|
|
||
|
if (hwlat_busy)
|
||
|
hwlat_tracer_start(tr);
|
||
|
mutex_unlock(&trace_types_lock);
|
||
|
|
||
|
*ppos += cnt;
|
||
|
|
||
|
|
||
|
|
||
|
return ret;
|
||
|
}
|
||
|
|
||
|
/*
|
||
|
* The width parameter is read/write using the generic trace_min_max_param
|
||
|
* method. The *val is protected by the hwlat_data lock and is upper
|
||
|
* bounded by the window parameter.
|
||
|
*/
|
||
|
static struct trace_min_max_param hwlat_width = {
|
||
|
.lock = &hwlat_data.lock,
|
||
|
.val = &hwlat_data.sample_width,
|
||
|
.max = &hwlat_data.sample_window,
|
||
|
.min = NULL,
|
||
|
};
|
||
|
|
||
|
/*
|
||
|
* The window parameter is read/write using the generic trace_min_max_param
|
||
|
* method. The *val is protected by the hwlat_data lock and is lower
|
||
|
* bounded by the width parameter.
|
||
|
*/
|
||
|
static struct trace_min_max_param hwlat_window = {
|
||
|
.lock = &hwlat_data.lock,
|
||
|
.val = &hwlat_data.sample_window,
|
||
|
.max = NULL,
|
||
|
.min = &hwlat_data.sample_width,
|
||
|
};
|
||
|
|
||
|
static const struct file_operations thread_mode_fops = {
|
||
|
.open = hwlat_mode_open,
|
||
|
.read = seq_read,
|
||
|
.llseek = seq_lseek,
|
||
|
.release = seq_release,
|
||
|
.write = hwlat_mode_write
|
||
|
};
|
||
|
/**
|
||
|
* init_tracefs - A function to initialize the tracefs interface files
|
||
|
*
|
||
|
* This function creates entries in tracefs for "hwlat_detector".
|
||
|
* It creates the hwlat_detector directory in the tracing directory,
|
||
|
* and within that directory is the count, width and window files to
|
||
|
* change and view those values.
|
||
|
*/
|
||
|
static int init_tracefs(void)
|
||
|
{
|
||
|
int ret;
|
||
|
struct dentry *top_dir;
|
||
|
|
||
|
ret = tracing_init_dentry();
|
||
|
if (ret)
|
||
|
return -ENOMEM;
|
||
|
|
||
|
top_dir = tracefs_create_dir("hwlat_detector", NULL);
|
||
|
if (!top_dir)
|
||
|
return -ENOMEM;
|
||
|
|
||
|
hwlat_sample_window = tracefs_create_file("window", TRACE_MODE_WRITE,
|
||
|
top_dir,
|
||
|
&hwlat_window,
|
||
|
&trace_min_max_fops);
|
||
|
if (!hwlat_sample_window)
|
||
|
goto err;
|
||
|
|
||
|
hwlat_sample_width = tracefs_create_file("width", TRACE_MODE_WRITE,
|
||
|
top_dir,
|
||
|
&hwlat_width,
|
||
|
&trace_min_max_fops);
|
||
|
if (!hwlat_sample_width)
|
||
|
goto err;
|
||
|
|
||
|
hwlat_thread_mode = trace_create_file("mode", TRACE_MODE_WRITE,
|
||
|
top_dir,
|
||
|
NULL,
|
||
|
&thread_mode_fops);
|
||
|
if (!hwlat_thread_mode)
|
||
|
goto err;
|
||
|
|
||
|
return 0;
|
||
|
|
||
|
err:
|
||
|
tracefs_remove(top_dir);
|
||
|
return -ENOMEM;
|
||
|
}
|
||
|
|
||
|
static void hwlat_tracer_start(struct trace_array *tr)
|
||
|
{
|
||
|
int err;
|
||
|
|
||
|
if (hwlat_data.thread_mode == MODE_PER_CPU)
|
||
|
err = start_per_cpu_kthreads(tr);
|
||
|
else
|
||
|
err = start_single_kthread(tr);
|
||
|
if (err)
|
||
|
pr_err(BANNER "Cannot start hwlat kthread\n");
|
||
|
}
|
||
|
|
||
|
static void hwlat_tracer_stop(struct trace_array *tr)
|
||
|
{
|
||
|
if (hwlat_data.thread_mode == MODE_PER_CPU)
|
||
|
stop_per_cpu_kthreads();
|
||
|
else
|
||
|
stop_single_kthread();
|
||
|
}
|
||
|
|
||
|
static int hwlat_tracer_init(struct trace_array *tr)
|
||
|
{
|
||
|
/* Only allow one instance to enable this */
|
||
|
if (hwlat_busy)
|
||
|
return -EBUSY;
|
||
|
|
||
|
hwlat_trace = tr;
|
||
|
|
||
|
hwlat_data.count = 0;
|
||
|
tr->max_latency = 0;
|
||
|
save_tracing_thresh = tracing_thresh;
|
||
|
|
||
|
/* tracing_thresh is in nsecs, we speak in usecs */
|
||
|
if (!tracing_thresh)
|
||
|
tracing_thresh = last_tracing_thresh;
|
||
|
|
||
|
if (tracer_tracing_is_on(tr))
|
||
|
hwlat_tracer_start(tr);
|
||
|
|
||
|
hwlat_busy = true;
|
||
|
|
||
|
return 0;
|
||
|
}
|
||
|
|
||
|
static void hwlat_tracer_reset(struct trace_array *tr)
|
||
|
{
|
||
|
hwlat_tracer_stop(tr);
|
||
|
|
||
|
/* the tracing threshold is static between runs */
|
||
|
last_tracing_thresh = tracing_thresh;
|
||
|
|
||
|
tracing_thresh = save_tracing_thresh;
|
||
|
hwlat_busy = false;
|
||
|
}
|
||
|
|
||
|
static struct tracer hwlat_tracer __read_mostly =
|
||
|
{
|
||
|
.name = "hwlat",
|
||
|
.init = hwlat_tracer_init,
|
||
|
.reset = hwlat_tracer_reset,
|
||
|
.start = hwlat_tracer_start,
|
||
|
.stop = hwlat_tracer_stop,
|
||
|
.allow_instances = true,
|
||
|
};
|
||
|
|
||
|
__init static int init_hwlat_tracer(void)
|
||
|
{
|
||
|
int ret;
|
||
|
|
||
|
mutex_init(&hwlat_data.lock);
|
||
|
|
||
|
ret = register_tracer(&hwlat_tracer);
|
||
|
if (ret)
|
||
|
return ret;
|
||
|
|
||
|
hwlat_init_hotplug_support();
|
||
|
|
||
|
init_tracefs();
|
||
|
|
||
|
return 0;
|
||
|
}
|
||
|
late_initcall(init_hwlat_tracer);
|