* What is the source of the time field in perf_sample events?
@ 2012-03-18 12:08 Bernie Pope
2012-04-06 17:14 ` David Ahern
0 siblings, 1 reply; 2+ messages in thread
From: Bernie Pope @ 2012-03-18 12:08 UTC (permalink / raw)
To: linux-perf-users
Hello,
I'm writing a tool to parse the perf.data output of perf and was wondering about the source of the timestamps found in perf_sample events? Specifically I mean the u64 time field in the perf_sample struct in util/event.h. I believe it is in nanoseconds from a particular event (system start?), but I can't find any documentation about where the time comes from.
I'm also interested in reading from this time source from a userspace program, is that possible?
Regards,
Bernie.
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: What is the source of the time field in perf_sample events?
2012-03-18 12:08 What is the source of the time field in perf_sample events? Bernie Pope
@ 2012-04-06 17:14 ` David Ahern
0 siblings, 0 replies; 2+ messages in thread
From: David Ahern @ 2012-04-06 17:14 UTC (permalink / raw)
To: Bernie Pope; +Cc: linux-perf-users
On 3/18/12 6:08 AM, Bernie Pope wrote:
> Hello,
>
> I'm writing a tool to parse the perf.data output of perf and was wondering about the source of the timestamps found in perf_sample events? Specifically I mean the u64 time field in the perf_sample struct in util/event.h. I believe it is in nanoseconds from a particular event (system start?), but I can't find any documentation about where the time comes from.
>
> I'm also interested in reading from this time source from a userspace program, is that possible?
Did you get a response to this?
Code wise, you'll need to follow perf_clock(). I believe for x86 with a
stable TSC you end up in native_sched_clock() in arch/x86/kernel/tsc.c.
As for the corresponding userspace call I believe it is
clock_gettime(CLOCK_MONOTONIC, ...).
David
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2012-03-18 12:08 What is the source of the time field in perf_sample events? Bernie Pope
2012-04-06 17:14 ` David Ahern
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