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

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Date:	Tue, 8 Mar 2016 18:56:01 +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 6:48 PM, Ingo Molnar <mingo@...nel.org> wrote:
>
> * Dmitry Vyukov <dvyukov@...gle.com> wrote:
>
>> 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.
>
> Things got a lot more lively after that!
>
> But most of the overhead seems to come from systemd trying to dump core or
> something like that:
>
>  85872 mingo     20   0   34712   3016   2656 S   4.6  0.0   0:00.14 systemd-coredum
>  85440 mingo     20   0   34712   3028   2664 S   4.2  0.0   0:00.13 systemd-coredum
>  85751 mingo     20   0   34712   3076   2716 S   4.2  0.0   0:00.13 systemd-coredum
>  85840 mingo     20   0   34712   2988   2624 S   4.2  0.0   0:00.13 systemd-coredum
>  85861 mingo     20   0   34712   3080   2720 S   4.2  0.0   0:00.13 systemd-coredum
>  85954 mingo     20   0   34712   3028   2664 S   4.2  0.0   0:00.13 systemd-coredum
>
> and I have:
>
>  fomalhaut:~/go/src/github.com/google/syzkaller> ulimit -c
>  0
>
> weird ... Has any of you seen such behavior?


I have not seen it.
Probably I need to directly disable core dumps within the syz-executor process.