linux-kernel - Re: [PATCH 3/5] perf core: Prepare writing into ring buffer from end

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Date:	Sun, 27 Mar 2016 17:20:05 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	"Wangnan (F)" <wangnan0@...wei.com>
Cc:	mingo@...hat.com, linux-kernel@...r.kernel.org,
	He Kuang <hekuang@...wei.com>,
	Alexei Starovoitov <ast@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Brendan Gregg <brendan.d.gregg@...il.com>,
	Jiri Olsa <jolsa@...nel.org>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Namhyung Kim <namhyung@...nel.org>,
	Zefan Li <lizefan@...wei.com>, pi3orama@....com
Subject: Re: [PATCH 3/5] perf core: Prepare writing into ring buffer from end

On Fri, Mar 25, 2016 at 10:14:36PM +0800, Wangnan (F) wrote:
> >>I think you enabled some unusual config options?

x86_64-defconfig

> >You must enabled CONFIG_OPTIMIZE_INLINING. Now I get similar result:

It has that indeed.

> After enabling CONFIG_OPTIMIZE_INLINING:
> 
> Test its performance by calling 'close(-1)' for 3000000 times and
> use 'perf record -o /dev/null -e raw_syscalls:* test-ring-buffer' to
> capture system calls:
> 
>                   MEAN         STDVAR
> BASE            800077.1     23448.13
> RAWPERF.PRE    2465858.0    603473.70
> RAWPERF.POST   2471925.0    609437.60
> 
> Considering the high stdvar, after applying this patch the performance
> is not change.

Why is your variance so immense? And doesn't that render the
measurements pointless?