trace-clock/x86-trace-clock

x86 trace clock

X86 trace clock. Depends on tsc_sync to detect if timestamp counters are
synchronized on the machine.

I am leaving this poorly scalable solution for now as this is the simplest, yet
working, solution I found (compared to using the HPET which also scales very
poorly, probably due to bus contention). This should be a good start and let us
trace a good amount of machines out there.

A "Big Fat" (TM) warning is shown on the console when the trace clock is used on
systems without synchronized TSCs to tell the user to

- use force_tsc_sync=1
- use idle=poll
- disable Powernow or Speedstep

In order to get accurate and fast timestamps.

This keeps room for further improvement in a second phase.

Changelog:
- freq_scale is not used as a divisor rather than multiplier to support systems
  with frequency < 1HZ.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
CC: Thomas Gleixner <tglx@linutronix.de>
CC: Ingo Molnar <mingo@redhat.com>
CC: H. Peter Anvin <hpa@zytor.com>
CC: Linus Torvalds <torvalds@linux-foundation.org>
CC: Andrew Morton <akpm@linux-foundation.org>
CC: Peter Zijlstra <a.p.zijlstra@chello.nl>
CC: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 1 insertions, 0 deletions

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index a87190ccf47..70b1eb3b8fd 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -31,6 +31,7 @@ config X86
 	select ARCH_WANT_FRAME_POINTERS
 	select HAVE_DMA_ATTRS
 	select HAVE_KRETPROBES
+	select HAVE_TRACE_CLOCK
 	select HAVE_OPTPROBES
 	select HAVE_FTRACE_MCOUNT_RECORD
 	select HAVE_C_RECORDMCOUNT