Date: Mon, 14 Dec 2015 17:56:14 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Namhyung Kim <namhyung@kernel.org>
Cc: Ingo Molnar <mingo@kernel.org>, David Ahern <dsahern@gmail.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Jiri Olsa <jolsa@redhat.com>, LKML <linux-kernel@vger.kernel.org>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Andi Kleen <andi@firstfloor.org>,
        Stephane Eranian <eranian@google.com>,
        Adrian Hunter <adrian.hunter@intel.com>
Subject: Re: [PATCHSET 00/16] perf top: Add multi-thread support (v1)
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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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