Messages in this thread | | | Date | Wed, 11 Dec 2013 12:25:26 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH] perf: POSIX CLOCK_PERF to report current time value |
| |
* David Ahern <dsahern@gmail.com> wrote:
> From: Pawel Moll <pawel.moll@arm.com> > > To co-relate user space events with the perf events stream > a current (as in: "what time(stamp) is it now?") time value > must be made available.
So I'm wondering about your earlier approach posted here:
https://lkml.org/lkml/2011/6/7/636
I'd modify that patch the following way: instead of tracking each separate reason, perhaps only track timekeeping_update().
Such a tracepoint, combined with PERF_SAMPLE_TIME, would very accurately track external changes to GTOD (xtime).
That leaves us with tracking/correlating the regular flow of time, which could be achieved by another tracepoint in:
kernel/time/timekeeping.c::do_timer()
So only two new tracepoints are needed AFAICS - and the tracepoints would obviously be useful for other (debugging) purposes as well. Would that solve the wall-clock correlation problem adequately?
Thanks,
Ingo
| |