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/kernel/Makefile b/arch/x86/kernel/Makefile
index c8664925391..717cf9c620b 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -46,6 +46,7 @@ obj-y			+= alternative.o i8253.o pci-nommu.o hw_breakpoint.o
 obj-y			+= tsc.o io_delay.o rtc.o
 obj-y			+= pci-iommu_table.o
 obj-y			+= resource.o
+obj-$(CONFIG_HAVE_TRACE_CLOCK)	+= trace-clock.o
 
 obj-$(CONFIG_X86_TRAMPOLINE)	+= trampoline.o
 obj-y				+= process.o