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

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Message-ID: <20160308180238.GA4220@gmail.com>
Date:	Tue, 8 Mar 2016 19:02:39 +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:

> 
> * 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 

So with that fixed, I finally started fuzzing for real.

With nproc set to 120 it seems to be chugging along at about 25% system 
utilization:

Tasks: 1271 total,   1 running, 1270 sleeping,   0 stopped,   0 zombie
%Cpu(s):  4.5 us, 35.3 sy,  0.0 ni, 55.2 id,  0.5 wa,  4.5 hi,  0.0 si,  0.0 st
KiB Mem : 26401230+total, 25401017+free,  1624640 used,  8377496 buff/cache
KiB Swap:        0 total,        0 free,        0 used. 26143329+avail Mem 

   PID USER      PR  NI    VIRT    RES    SHR S  %CPU %MEM     TIME+ COMMAND                                                                                                          
 87593 mingo     20   0 7850436 162284  11672 S  2941  0.1  33:01.83 syz-fuzzer                                                                                                       
   923 root      20   0   84772  44344  43840 S  22.8  0.0   1:23.86 systemd-journal                                                                                                  
  1369 root      16  -4  114636   3256   2832 S  15.7  0.0   0:29.03 auditd                                                                                                           
  1379 root      12  -8   80236   1764   1432 S   8.3  0.0   0:15.79 audispd                                                                                                          
   878 root      20   0       0      0      0 S   6.9  0.0   0:16.55 jbd2/sda1-8                                                                                                      
  1381 root      16  -4   52216   3232   2892 S   3.8  0.0   0:07.08 sedispatch              

Even that one is not ideal - obviously there's way too much systemd-journal 
overhead, but I'm unable to turn the darn thing off ...

with nproc=480 it does not seem to be working very well - it quickly generates:

2016/03/08 18:59:38 local-0: lost connection: exit status 2
2016/03/08 18:59:38 local-0: saving crash 'lost connection' to crash-local-0-1457459978295423413

and then after some time starts to ramp up again. It's mostly idling around.

Thanks,

	Ingo