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

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Date:	Tue, 8 Mar 2016 18:57:53 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Dmitry Vyukov <dvyukov@...gle.com>
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


* Ingo Molnar <mingo@...nel.org> wrote:

> 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?

So the workaround for that is to disable systemd trying to log every core dump to 
the system journal (!), via:

  echo > /proc/sys/kernel/core_pattern 

Thanks,

	Ingo