Date: Tue, 15 Dec 2015 02:11:43 +0900
From: Namhyung Kim <namhyung@kernel.org>
To: Peter Zijlstra <peterz@infradead.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 Mon, Dec 14, 2015 at 05:56:14PM +0100, Peter Zijlstra wrote:
> 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.

Right.  Now I recall that it was about *report* (not record) time
accessing single file vs. multi files.

At record time we should use file per cpu.  I combined them into
one with index at post-processing time in my earlier work.

Thanks for clarification!
Namhyung
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