linux-kernel - Re: [RESEND PATCH 0/5] perf core: Support overwrite ring buffer

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Date:	Tue, 8 Mar 2016 18:41:52 +0100
From:	Dmitry Vyukov <dvyukov@...gle.com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Wang Nan <wangnan0@...wei.com>, Ingo Molnar <mingo@...hat.com>,
	LKML <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: [RESEND PATCH 0/5] perf core: Support overwrite ring buffer

On Tue, Mar 8, 2016 at 6:37 PM, Ingo Molnar <mingo@...nel.org> wrote:
>
> * Dmitry Vyukov <dvyukov@...gle.com> wrote:
>
>> > fomalhaut:~/go/src/github.com/google/syzkaller> ps aux | grep -i syz
>> > mingo      1374  0.0  0.0 118476  2376 pts/2    S+   18:23   0:00 grep --color=auto -i syz
>> >
>> > and with no kernel messages in dmesg - and with a fully functional system.
>> >
>> > I'm running the 16-task load on a 120 CPU system - should I increase it to 120?
>> > Does the code expect to saturate the system?
>>
>> No, it does not expect to saturate the system. Set "procs" to 480, or
>> something like that.
>
> Does not seem to help much:
>
> fomalhaut:~> vmstat 10
> procs -----------memory---------- ---swap-- -----io---- -system-- ------cpu-----
>  r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy id wa st
>
>  1  0      0 257465904 219940 4736092    0    0     0   102 16022 4396  0  1 99  0  0
>  2  0      0 257452144 220496 4755052    0    0     2  3649 14286 4627  0  1 99  0  0
>  2  0      0 257473408 221188 4770824    0    0    15  1898 17175 4474  0  1 99  0  0
>
> Only around 1% system utilization. Should I go for 1,000 or more? :)
>
> Peter, do you experience with running syz-kaller on larger CPU count Intel
> systems?


Try to set "dropprivs": false in config.
I've noticed that creation/destruction of namespaces is very slow and
globally serialized. So sometimes it takes tens of seconds for each
worker processes to startup. For perf-related syscalls it should be
"safe" to just run as root. And perf subsystem operation is also
unaffected by namespaces as far as I know, so it should not affect
behavior as well.