Re: [PATCH 1/2] perf tools: Add reference timestamp to perf header

[Peter Zijlstra]

On Mon, 2010-12-13 at 12:15 -0700, David S. Ahern wrote:
> >   monotonic-clock
> 
> Name seems off. The 'event' is to grab time-of-day and have the 'time'
> attribute set which gives the correlation between wall-clock and perf
> timestamps. 

Well, you really want CLOCK_MONOTONIC, not CLOCK_REALTIME (nothing what
so ever to do with Real-Time computing, just another brilliant POSIX
misnomer), or possibly even CLOCK_MONOTONIC_RAW.

gettimeofday() usually returns CLOCK_REALTIME  which is subject to both
NTP and timezone adjustments.

CLOCK_MONOTONIC is only subject to NTP

CLOCK_MONOTONIC_RAW is neither.

At some point we'll try and have CLOCK_TRACING and provide a similar
time to user-space that we currently use for perf (using the VDSO to
avoid any actual system-calls).


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