linux-kernel - Re: [PATCH 0/9] perf: Adding better precise

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Message-ID: <20130514083621.GA20995@redhat.com>
Date:	Tue, 14 May 2013 11:36:21 +0300
From:	Gleb Natapov <gleb@...hat.com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Jiri Olsa <jolsa@...hat.com>, linux-kernel@...r.kernel.org,
	Corey Ashford <cjashfor@...ux.vnet.ibm.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...e.hu>,
	Namhyung Kim <namhyung@...nel.org>,
	Paul Mackerras <paulus@...ba.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Andi Kleen <ak@...ux.intel.com>,
	David Ahern <dsahern@...il.com>,
	Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH 0/9] perf: Adding better precise_ip field handling

On Mon, May 13, 2013 at 09:43:13PM +0200, Ingo Molnar wrote:
> Note that at least for user-space, REP MOVS is getting rarer. libc uses 
> SSE based memcpy/memset variants - which is not miscounted by PEBS. The 
> kernel still uses REP MOVS - but it's a special case because it cannot 
> cheaply use vector registers.
> 
> The vast majority of code gets measured by cycles:pp more accurately than 
> cycles.
> 
> We could try and see how many people complain. It's not like it's hard to 
> undo such a change of the default event?
> 
People may optimize for a wrong case instead of complaining. There is
nothing that obviously broken, only if you know what to look for the
brokenness can be seen.

--
			Gleb.
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