linux-kernel - Re: perf samples too long without perf running (?!?)

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Message-ID: <CALCETrW5Gpz7TYVVj2NxbKx4cFdePUQ1sEPDyLt5qLmy7KCycQ@mail.gmail.com>
Date:	Sat, 8 Mar 2014 08:22:16 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	Markus Trippelsdorf <markus@...ppelsdorf.de>
Cc:	Mike Galbraith <umgwanakikbuti@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: perf samples too long without perf running (?!?)

On Sat, Mar 8, 2014 at 1:13 AM, Markus Trippelsdorf
<markus@...ppelsdorf.de> wrote:
> On 2014.03.08 at 08:51 +0100, Mike Galbraith wrote:
>> On Fri, 2014-03-07 at 17:57 -0800, Andy Lutomirski wrote:
>> > On recent (3.13) kernels, I'm frequently getting messages like:
>> >
>> > perf samples too long (2503 > 2500), lowering
>> > kernel.perf_event_max_sample_rate to 50000
>> >
>> > a few seconds to minutes after bootup.  As far as I know, I'm not
>> > using perf.  What's going on here?
>>
>> 14c63f17b1
>>
>> I get those all the time too, just building kernels.
>
> I have:
>  echo 0 > /proc/sys/kernel/perf_cpu_time_max_percent
> in my local startup script since that commit.

...so the NMI watchdog (which happens IIRC once every two minutes)
takes more than 0.4ms or so, so perf flips out, changes its parameters,
and writes a log message.

Is it just me or is this whole situation screwed up for multiple reasons?

--Andy

>
> --
> Markus



-- 
Andy Lutomirski
AMA Capital Management, LLC
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