Pull request

Stefano's performance regression fix for commit 2558cb8dd4 ("linux-aio:
 increasing MAX_EVENTS to a larger hardcoded value").
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Merge remote-tracking branch 'remotes/stefanha-gitlab/tags/block-pull-request' into staging

Pull request

Stefano's performance regression fix for commit 2558cb8dd4 ("linux-aio:
increasing MAX_EVENTS to a larger hardcoded value").

# gpg: Signature made Wed 21 Jul 2021 14:12:47 BST
# gpg:                using RSA key 8695A8BFD3F97CDAAC35775A9CA4ABB381AB73C8
# gpg: Good signature from "Stefan Hajnoczi <stefanha@redhat.com>" [full]
# gpg:                 aka "Stefan Hajnoczi <stefanha@gmail.com>" [full]
# Primary key fingerprint: 8695 A8BF D3F9 7CDA AC35  775A 9CA4 ABB3 81AB 73C8

* remotes/stefanha-gitlab/tags/block-pull-request:
  linux-aio: limit the batch size using `aio-max-batch` parameter
  iothread: add aio-max-batch parameter
  iothread: generalize iothread_set_param/iothread_get_param

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

block/linux-aio.c

@@ -28,6 +28,9 @@
  */
 #define MAX_EVENTS 1024
 
+/* Maximum number of requests in a batch. (default value) */
+#define DEFAULT_MAX_BATCH 32
+
 struct qemu_laiocb {
     Coroutine *co;
     LinuxAioState *ctx;
@@ -351,6 +354,10 @@ static int laio_do_submit(int fd, struct qemu_laiocb *laiocb, off_t offset,
     LinuxAioState *s = laiocb->ctx;
     struct iocb *iocbs = &laiocb->iocb;
     QEMUIOVector *qiov = laiocb->qiov;
+    int64_t max_batch = s->aio_context->aio_max_batch ?: DEFAULT_MAX_BATCH;
+
+    /* limit the batch with the number of available events */
+    max_batch = MIN_NON_ZERO(MAX_EVENTS - s->io_q.in_flight, max_batch);
 
     switch (type) {
     case QEMU_AIO_WRITE:
@@ -371,7 +378,7 @@ static int laio_do_submit(int fd, struct qemu_laiocb *laiocb, off_t offset,
     s->io_q.in_queue++;
     if (!s->io_q.blocked &&
         (!s->io_q.plugged ||
-         s->io_q.in_flight + s->io_q.in_queue >= MAX_EVENTS)) {
+         s->io_q.in_queue >= max_batch)) {
         ioq_submit(s);
     }
 

include/block/aio.h

@@ -232,6 +232,9 @@ struct AioContext {
     int64_t poll_grow;      /* polling time growth factor */
     int64_t poll_shrink;    /* polling time shrink factor */
 
+    /* AIO engine parameters */
+    int64_t aio_max_batch;  /* maximum number of requests in a batch */
+
     /*
      * List of handlers participating in userspace polling.  Protected by
      * ctx->list_lock.  Iterated and modified mostly by the event loop thread
@@ -755,4 +758,13 @@ void aio_context_set_poll_params(AioContext *ctx, int64_t max_ns,
                                  int64_t grow, int64_t shrink,
                                  Error **errp);
 
+/**
+ * aio_context_set_aio_params:
+ * @ctx: the aio context
+ * @max_batch: maximum number of requests in a batch, 0 means that the
+ *             engine will use its default
+ */
+void aio_context_set_aio_params(AioContext *ctx, int64_t max_batch,
+                                Error **errp);
+
 #endif

include/sysemu/iothread.h

@@ -37,6 +37,9 @@ struct IOThread {
     int64_t poll_max_ns;
     int64_t poll_grow;
     int64_t poll_shrink;
+
+    /* AioContext AIO engine parameters */
+    int64_t aio_max_batch;
 };
 typedef struct IOThread IOThread;
 

iothread.c

@@ -152,6 +152,24 @@ static void iothread_init_gcontext(IOThread *iothread)
     iothread->main_loop = g_main_loop_new(iothread->worker_context, TRUE);
 }
 
+static void iothread_set_aio_context_params(IOThread *iothread, Error **errp)
+{
+    ERRP_GUARD();
+
+    aio_context_set_poll_params(iothread->ctx,
+                                iothread->poll_max_ns,
+                                iothread->poll_grow,
+                                iothread->poll_shrink,
+                                errp);
+    if (*errp) {
+        return;
+    }
+
+    aio_context_set_aio_params(iothread->ctx,
+                               iothread->aio_max_batch,
+                               errp);
+}
+
 static void iothread_complete(UserCreatable *obj, Error **errp)
 {
     Error *local_error = NULL;
@@ -171,11 +189,7 @@ static void iothread_complete(UserCreatable *obj, Error **errp)
      */
     iothread_init_gcontext(iothread);
 
-    aio_context_set_poll_params(iothread->ctx,
+    iothread_set_aio_context_params(iothread, &local_error);
-                                iothread->poll_max_ns,
-                                iothread->poll_grow,
-                                iothread->poll_shrink,
-                                &local_error);
     if (local_error) {
         error_propagate(errp, local_error);
         aio_context_unref(iothread->ctx);
@@ -212,8 +226,11 @@ static PollParamInfo poll_grow_info = {
 static PollParamInfo poll_shrink_info = {
     "poll-shrink", offsetof(IOThread, poll_shrink),
 };
+static PollParamInfo aio_max_batch_info = {
+    "aio-max-batch", offsetof(IOThread, aio_max_batch),
+};
 
-static void iothread_get_poll_param(Object *obj, Visitor *v,
+static void iothread_get_param(Object *obj, Visitor *v,
         const char *name, void *opaque, Error **errp)
 {
     IOThread *iothread = IOTHREAD(obj);
@@ -223,7 +240,7 @@ static void iothread_get_poll_param(Object *obj, Visitor *v,
     visit_type_int64(v, name, field, errp);
 }
 
-static void iothread_set_poll_param(Object *obj, Visitor *v,
+static bool iothread_set_param(Object *obj, Visitor *v,
         const char *name, void *opaque, Error **errp)
 {
     IOThread *iothread = IOTHREAD(obj);
@@ -232,17 +249,36 @@ static void iothread_set_poll_param(Object *obj, Visitor *v,
     int64_t value;
 
     if (!visit_type_int64(v, name, &value, errp)) {
-        return;
+        return false;
     }
 
     if (value < 0) {
         error_setg(errp, "%s value must be in range [0, %" PRId64 "]",
                    info->name, INT64_MAX);
-        return;
+        return false;
     }
 
     *field = value;
 
+    return true;
+}
+
+static void iothread_get_poll_param(Object *obj, Visitor *v,
+        const char *name, void *opaque, Error **errp)
+{
+
+    iothread_get_param(obj, v, name, opaque, errp);
+}
+
+static void iothread_set_poll_param(Object *obj, Visitor *v,
+        const char *name, void *opaque, Error **errp)
+{
+    IOThread *iothread = IOTHREAD(obj);
+
+    if (!iothread_set_param(obj, v, name, opaque, errp)) {
+        return;
+    }
+
     if (iothread->ctx) {
         aio_context_set_poll_params(iothread->ctx,
                                     iothread->poll_max_ns,
@@ -252,6 +288,29 @@ static void iothread_set_poll_param(Object *obj, Visitor *v,
     }
 }
 
+static void iothread_get_aio_param(Object *obj, Visitor *v,
+        const char *name, void *opaque, Error **errp)
+{
+
+    iothread_get_param(obj, v, name, opaque, errp);
+}
+
+static void iothread_set_aio_param(Object *obj, Visitor *v,
+        const char *name, void *opaque, Error **errp)
+{
+    IOThread *iothread = IOTHREAD(obj);
+
+    if (!iothread_set_param(obj, v, name, opaque, errp)) {
+        return;
+    }
+
+    if (iothread->ctx) {
+        aio_context_set_aio_params(iothread->ctx,
+                                   iothread->aio_max_batch,
+                                   errp);
+    }
+}
+
 static void iothread_class_init(ObjectClass *klass, void *class_data)
 {
     UserCreatableClass *ucc = USER_CREATABLE_CLASS(klass);
@@ -269,6 +328,10 @@ static void iothread_class_init(ObjectClass *klass, void *class_data)
                               iothread_get_poll_param,
                               iothread_set_poll_param,
                               NULL, &poll_shrink_info);
+    object_class_property_add(klass, "aio-max-batch", "int",
+                              iothread_get_aio_param,
+                              iothread_set_aio_param,
+                              NULL, &aio_max_batch_info);
 }
 
 static const TypeInfo iothread_info = {
@@ -318,6 +381,7 @@ static int query_one_iothread(Object *object, void *opaque)
     info->poll_max_ns = iothread->poll_max_ns;
     info->poll_grow = iothread->poll_grow;
     info->poll_shrink = iothread->poll_shrink;
+    info->aio_max_batch = iothread->aio_max_batch;
 
     QAPI_LIST_APPEND(*tail, info);
     return 0;

monitor/hmp-cmds.c

@@ -1893,6 +1893,8 @@ void hmp_info_iothreads(Monitor *mon, const QDict *qdict)
         monitor_printf(mon, "  poll-max-ns=%" PRId64 "\n", value->poll_max_ns);
         monitor_printf(mon, "  poll-grow=%" PRId64 "\n", value->poll_grow);
         monitor_printf(mon, "  poll-shrink=%" PRId64 "\n", value->poll_shrink);
+        monitor_printf(mon, "  aio-max-batch=%" PRId64 "\n",
+                       value->aio_max_batch);
     }
 
     qapi_free_IOThreadInfoList(info_list);

qapi/misc.json

@@ -86,6 +86,9 @@
 # @poll-shrink: how many ns will be removed from polling time, 0 means that
 #               it's not configured (since 2.9)
 #
+# @aio-max-batch: maximum number of requests in a batch for the AIO engine,
+#                 0 means that the engine will use its default (since 6.1)
+#
 # Since: 2.0
 ##
 { 'struct': 'IOThreadInfo',
@@ -93,7 +96,8 @@
            'thread-id': 'int',
            'poll-max-ns': 'int',
            'poll-grow': 'int',
-           'poll-shrink': 'int' } }
+           'poll-shrink': 'int',
+           'aio-max-batch': 'int' } }
 
 ##
 # @query-iothreads:

qapi/qom.json

@@ -516,12 +516,17 @@
 #               algorithm detects it is spending too long polling without
 #               encountering events. 0 selects a default behaviour (default: 0)
 #
+# @aio-max-batch: maximum number of requests in a batch for the AIO engine,
+#                 0 means that the engine will use its default
+#                 (default:0, since 6.1)
+#
 # Since: 2.0
 ##
 { 'struct': 'IothreadProperties',
   'data': { '*poll-max-ns': 'int',
             '*poll-grow': 'int',
-            '*poll-shrink': 'int' } }
+            '*poll-shrink': 'int',
+            '*aio-max-batch': 'int' } }
 
 ##
 # @MemoryBackendProperties:

qemu-options.hx

@@ -5301,7 +5301,7 @@ SRST
 
             CN=laptop.example.com,O=Example Home,L=London,ST=London,C=GB
 
-    ``-object iothread,id=id,poll-max-ns=poll-max-ns,poll-grow=poll-grow,poll-shrink=poll-shrink``
+    ``-object iothread,id=id,poll-max-ns=poll-max-ns,poll-grow=poll-grow,poll-shrink=poll-shrink,aio-max-batch=aio-max-batch``
         Creates a dedicated event loop thread that devices can be
         assigned to. This is known as an IOThread. By default device
         emulation happens in vCPU threads or the main event loop thread.
@@ -5337,7 +5337,11 @@ SRST
         the polling time when the algorithm detects it is spending too
         long polling without encountering events.
 
-        The polling parameters can be modified at run-time using the
+        The ``aio-max-batch`` parameter is the maximum number of requests
+        in a batch for the AIO engine, 0 means that the engine will use
+        its default.
+
+        The IOThread parameters can be modified at run-time using the
         ``qom-set`` command (where ``iothread1`` is the IOThread's
         ``id``):
 

util/aio-posix.c

@@ -716,3 +716,15 @@ void aio_context_set_poll_params(AioContext *ctx, int64_t max_ns,
 
     aio_notify(ctx);
 }
+
+void aio_context_set_aio_params(AioContext *ctx, int64_t max_batch,
+                                Error **errp)
+{
+    /*
+     * No thread synchronization here, it doesn't matter if an incorrect value
+     * is used once.
+     */
+    ctx->aio_max_batch = max_batch;
+
+    aio_notify(ctx);
+}

util/aio-win32.c

@@ -440,3 +440,8 @@ void aio_context_set_poll_params(AioContext *ctx, int64_t max_ns,
         error_setg(errp, "AioContext polling is not implemented on Windows");
     }
 }
+
+void aio_context_set_aio_params(AioContext *ctx, int64_t max_batch,
+                                Error **errp)
+{
+}

util/async.c

@@ -554,6 +554,8 @@ AioContext *aio_context_new(Error **errp)
     ctx->poll_grow = 0;
     ctx->poll_shrink = 0;
 
+    ctx->aio_max_batch = 0;
+
     return ctx;
 fail:
     g_source_destroy(&ctx->source);