linux-kernel - Re: [PATCH RFC V3 3/5] perf,tool: partial time support

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Message-ID: <20150714010449.GB16880@danjae.kornet>
Date:	Tue, 14 Jul 2015 10:04:49 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	"Liang, Kan" <kan.liang@...el.com>
Cc:	"acme@...nel.org" <acme@...nel.org>,
	"jolsa@...nel.org" <jolsa@...nel.org>,
	"ak@...ux.intel.com" <ak@...ux.intel.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Hunter, Adrian" <adrian.hunter@...el.com>
Subject: Re: [PATCH RFC V3 3/5] perf,tool: partial time support

On Mon, Jul 13, 2015 at 07:01:51PM +0000, Liang, Kan wrote:
> > On Wed, Jul 08, 2015 at 04:44:55AM -0400, kan.liang@...el.com wrote:
> > > From: Kan Liang <kan.liang@...el.com>
> > >
> > > When multiple events are sampled it may not be needed to collect fine
> > > grained time stamps on all events. The sample sites are usually nearby.
> > > It's enough to have time stamps on the regular reference events.
> > > This patchkit adds the ability to turn off time stamps per event. This
> > > in term can reduce sampling overhead and the size of the perf.data.
> > 
> > So this patch makes the PERF_SAMPLE_TIME bit set or not independently,
> > right?  But AFAIK we sometimes just use first evsel for checking
> > sample_type value, especially for evlist->id_pos.  I'm not sure it'll work for
> > all cases of mixed time/notime events..
> >
> 
> If the sample_type is different, IDENTIFIER will be set to make sure id is in
> a fixed position. So we don't need to worry about evlist->id_pos here.
> 
> I think the only unsupported case should be that the kernel doesn't
> support IDENTIFIER.  If so, under my test, perf record will print warning
> " failed to process type". Perf report will also print warning
> " non matching sample_type". So the user can switch back to full time
> support.

Ah, ok then.


> If you think the warning is not good enough, we can show specific
> warning and error out when non IDENTIFIER support is detected.

Well, I think it's good enough. :)

However, perf_evlist__id_hdr_size() seems to be affected also.  Are
you sure it's okay too?

Thanks,
Namhyung
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