Messages in this thread | | | Date | Mon, 13 Dec 2010 17:08:31 -0200 | From | Arnaldo Carvalho de Melo <> | Subject | Re: [PATCH 1/2] perf tools: Add reference timestamp to perf header |
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Em Mon, Dec 13, 2010 at 11:01:13AM -0700, David S. Ahern escreveu: > On 12/13/10 10:57, Peter Zijlstra wrote: > >> What about creating a PERF_RECORD_TIME and generate an event when the > >> counter is opened? It contains a PERF_SAMPLE_TIME and say > >> PERF_SAMPLE_TOD (time-of-day)? We're not sending rockets to saturn; we > >> just need the timestamps to match other log files.
> > That's similar to the first thing I proposed. The problem is with long > > record sessions your drift can become quite significant, then when you > > merge sort your other log events stuff can get out of order. Which can > > lead to some serious head-scratching..
> Gotcha. Missed that in the flury of emails.
> Arnaldo: Are you ok with this option? This should append mode as well.
What option, this one:
----------------------------------------------------------------------- Peter Zijlstra wrote:
> In fact, the only sane way to do that is by creating a software counter > that represents CLOCK_MONOTONIC and sample that say once a minute (or > more often if you want smaller drift). -----------------------------------------------------------------------
?
Yes, that looks the best option. I.e. no changes on headers, no new user fake events, a new software event that may be useful for other usecases.
We have:
[acme@mica linux]$ perf list | grep -- -clock cpu-clock [Software event] task-clock [Software event] [acme@mica linux]$
So we would have a new one:
monotonic-clock
Peter, agreed? I'll try to implement it now, good opportunity to learn a bit more about soft pmus, I'd have to do that anyway for NIC stats, etc.
- Arnaldo
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