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From: Dmitry Vyukov <dvyukov@google.com>
Date: Tue, 8 Mar 2016 18:56:01 +0100
Message-ID: <CACT4Y+Z7ej68TpVnkOTCru3jh0swAS-+ZjP4E3dOxOwvYXn7Rg@mail.gmail.com>
Subject: Re: [RESEND PATCH 0/5] perf core: Support overwrite ring buffer
To: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>, Wang Nan <wangnan0@huawei.com>,
        Ingo Molnar <mingo@redhat.com>, LKML <linux-kernel@vger.kernel.org>,
        He Kuang <hekuang@huawei.com>, Alexei Starovoitov <ast@kernel.org>,
        Arnaldo Carvalho de Melo <acme@redhat.com>,
        Brendan Gregg <brendan.d.gregg@gmail.com>,
        Jiri Olsa <jolsa@kernel.org>,
        Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>,
        Namhyung Kim <namhyung@kernel.org>, Zefan Li <lizefan@huawei.com>,
        pi3orama@163.com
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On Tue, Mar 8, 2016 at 6:48 PM, Ingo Molnar <mingo@kernel.org> wrote:
>
> * Dmitry Vyukov <dvyukov@google.com> wrote:
>
>> On Tue, Mar 8, 2016 at 6:37 PM, Ingo Molnar <mingo@kernel.org> wrote:
>> >
>> > * Dmitry Vyukov <dvyukov@google.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.