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

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Message-ID: <1270760136.20295.3121.camel@laptop>
Date:	Thu, 08 Apr 2010 22:55:36 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	eranian@...gle.com
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, paulus@...ba.org,
	davem@...emloft.net, fweisbec@...il.com, 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, 2010-04-08 at 22:45 +0200, Stephane Eranian wrote:
> 	There is a warn_on_once() check for PERF_SAMPLE_RAW which trips
> 	when using PEBS on both Core and Nehalem. Core PEBS sample size is 144
> 	bytes and 176 bytes for Nehalem. Both are multiples of 8, but the size
> 	field is encoded as int, thus the total is never a multiple of 8 which
> 	trips the check. I think the size should have been u64, but now it is
> 	too late to change given it is ABI.

PEBS hasn't seen -linus yet, so we can fix that.

There's various things that do indeed rely on the perf buffer to always
be u64 aligned, so this warning isn't bogus at all.

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