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

Ingo Molnar
2016-03-08T17:49:15Z

* 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?

Thanks,

Ingo