linux-kernel - Re: [PATCHSET 00/16] perf top: Add multi-thread support (v1)

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Message-ID: <20151214165614.GV6357@twins.programming.kicks-ass.net>
Date:	Mon, 14 Dec 2015 17:56:14 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Namhyung Kim <namhyung@...nel.org>
Cc:	Ingo Molnar <mingo@...nel.org>, David Ahern <dsahern@...il.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Jiri Olsa <jolsa@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Andi Kleen <andi@...stfloor.org>,
	Stephane Eranian <eranian@...gle.com>,
	Adrian Hunter <adrian.hunter@...el.com>
Subject: Re: [PATCHSET 00/16] perf top: Add multi-thread support (v1)

On Tue, Dec 15, 2015 at 01:38:30AM +0900, Namhyung Kim wrote:
> It requires many changes, but basically I also like the split-up since
> it's easier to deal with.  IIRC there was an opinion (Andi?) regarding
> single-file vs multi-file.  The file access will be better for single
> file so I changed my earlier implementation to use indexed single data
> file instead of multiple files.

The page-cache has a lock per inode, so by having all CPUs populate the
one file you get contention on that.

Also, I suppose you'll have to arbitrate ranges in that file for each
cpu to make it work, that too could get you some contention.

Having a file per cpu avoids all that.
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