Calculate the bus frequency at runtime

The 100mHz value was guaranteed by intel for this CPU,
but this approach is more reliable

pt-dump-decoder/src/lib.rs

@@ -6,7 +6,7 @@ use std::error::Error;
 use std::fs::File;
 use std::path::Path;
 use std::time::Duration;
-use raw_cpuid::CpuId;
+use raw_cpuid::{cpuid, CpuId};
 
 #[derive(Debug)]
 pub struct AnalyzeData {
@@ -38,8 +38,9 @@ pub fn analyze_dump(path: impl AsRef<Path>) -> Result<AnalyzeData, Box<dyn Error
     let mut segments = vec![(Scope::PreRun, Duration::ZERO)];
     let mut total = 0u64;
 
-    // Lets assume 100Mhz bus frequency (TODO compute that automatically)
-    let f_bus = 100_000_000.0;
+    // cpuid(0x16):ecx returns the bus frequency in mHz (See volume 2, chapter 1.3 CPUID in the intel manual)
+    // Combined with the core to bus ration we can calculate the core frequency
+    let f_bus = cpuid!(0x16).ecx as f64 * 1_000_000.0;
     let mut current_cbr = 0u8;
 
     let mut first_tsc = None::<u64>;