linux-kernel - Re: [PATCH] perf_events: fix bogus warn_on(_once) in perf_prepare

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Date:	Thu, 8 Apr 2010 23:46:18 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Stephane Eranian <eranian@...gle.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org, mingo@...e.hu, paulus@...ba.org,
	davem@...emloft.net, robert.richter@....com,
	perfmon2-devel@...ts.sf.net, eranian@...il.com
Subject: Re: [PATCH] perf_events: fix bogus warn_on(_once) in
	perf_prepare_sample()

On Thu, Apr 08, 2010 at 11:22:05PM +0200, Stephane Eranian wrote:
> On Thu, Apr 8, 2010 at 11:17 PM, Frederic Weisbecker <fweisbec@...il.com> wrote:
> > On Thu, Apr 08, 2010 at 11:14:15PM +0200, Stephane Eranian wrote:
> >> On Thu, Apr 8, 2010 at 11:11 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> >> > On Thu, 2010-04-08 at 23:08 +0200, Stephane Eranian wrote:
> >> >>
> >> >> Are you suggesting you add some padding the PEBS raw sample you
> >> >> return as PERF_SAMPLE_RAW? Then you need to define what RAW
> >> >> actually means? Seems here, it would mean more than what the
> >> >> HW returns.
> >> >
> >> > Well, RAW doesn't mean anything much at all, its really a fugly pass
> >> > some crap around thing.
> >> >
> >> > So yeah, adding padding seems just fine.
> >> >
> >> I would rather see size as u64. Who's using raw today anyway?
> >
> >
> > The trace events. Hence the size of the size shouldn't be touched, it
> > is an ABI now.
> 
> Given your alignment constraints, it seems like it was a bad choice to pick
> u32 for size to begin with.


Ah I remember now how we did that. We align the trace events raw sample size
such that sizeof(raw_sample) + sizeof(size) is aligned to u64.

Well, indeed that complexifies a bit the raw_sample size handling but at least
it makes the traces a bit more compact.

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