Re: [PATCH v5] perf: Use monotonic clock as a source for timestamps

Afternoon, Peter,

On Wed, 2015-01-21 at 20:27 +0000, Pawel Moll wrote:

Until now, perf framework never defined the meaning of the timestamps
captured as PERF_SAMPLE_TIME sample type. The values were obtaining
from local (sched) clock, which is unavailable in userspace. This made
it impossible to correlate perf data with any other events. Other
tracing solutions have the source configurable (ftrace) or just share
a common time domain between kernel and userspace (LTTng).

Follow the trend by using monotonic clock, which is readily available
as POSIX CLOCK_MONOTONIC.

Also add a sysctl "perf_sample_time_clk_id" attribute (usually available
as "/proc/sys/kernel/perf_sample_time_clk_id") which can be used by the
user to obtain the clk_id to be used with POSIX clock API (eg.
clock_gettime()) to obtain a time value comparable with perf samples.

Old behaviour can be restored by using "perf_use_local_clock" kernel
parameter.

Signed-off-by: Pawel Moll <redacted>

I know that you're busy with other stuff, but it's already rc7 time
again... We can leave the other two patches from the series for later,
but how about getting this one merged for 3.20 and ending the 2 or 3
years long struggle? I'm not saying that everyone is happy about it, but
no one seems to be unhappy enough to speak :-)

Cheers!

Pawel