Messages in this thread | | | Date | Mon, 13 Dec 2010 10:36:39 -0700 | From | "David S. Ahern" <> | Subject | Re: [PATCH 1/2] perf tools: Add reference timestamp to perf header |
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On 12/13/10 09:48, Arnaldo Carvalho de Melo wrote: > Em Mon, Dec 13, 2010 at 04:54:56PM +0100, Frederic Weisbecker escreveu: >> On Mon, Dec 13, 2010 at 07:39:24AM -0700, David S. Ahern wrote: >>> On 12/12/10 13:16, Frederic Weisbecker wrote: >>>>> int perf_session__create_kernel_maps(struct perf_session *self) >>>>> { >>>>> int ret = machine__create_kernel_maps(&self->host_machine); >>>>> @@ -167,6 +190,9 @@ struct perf_session *perf_session__new(const char *filename, int mode, bool forc >>>>> */ >>>>> if (perf_session__create_kernel_maps(self) < 0) >>>>> goto out_delete; >>>>> + >>>>> + if (perf_session__create_ref_time(self) < 0) >>>>> + goto out_delete; > >>>> So, it does record it anytime? > >>> Simplest to always add it the header as it does no harm if not used. >>> To make it conditional means adding an input parameter to >>> perf_session__new() and then updating all the callers. > >>> Is the preference to make it conditional? > >> No, I suspect the overhead is plain unnoticeable. And if it becomes >> any problem one day, we can still make that conditional later. > > Right, but it just ocurred to me, can't we encode this in the file stat?
I would not want to rely on stat output for timestamps. eg., copy that file off box and not have the timestamp preserved.
> Also, how do we deal with: > > $ perf record --help > <SNIP> > -A, --append > Append to the output file to do incremental profiling. > <SNIP> > > ?
Is it realistic to expect/allow an append using different perf binaries? That just seems plain odd. Then, if one invocation used --timehist and another did not output would be bizarre. Of course an append with a reboot between tests would cause problems as well.
> > I now think this should be implemented as a PERF_RECORD_WALL_CLOCK > synthesized event, to be inserted just before we start collecting the > other events. > > That way, when --appending, we just insert another and use that from > that point on. > > Look at tools/perf/util/event.h, enum perf_user_event_type and look how > those are synthesized.
I see the thread on this part. I don't have preference; just let me know what the final decision is. ie., synthesized event versus header entry.
David
> > Thanks, > > - Arnaldo
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