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

Dmitry Vyukov
2016-03-08T17:56:38Z

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.