linux-kernel - Re: sched: RT throttling activated, 3.12.3

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Message-ID: <52A7D74D.7000804@symas.com>
Date:	Tue, 10 Dec 2013 19:09:01 -0800
From:	Howard Chu <hyc@...as.com>
To:	Li Zefan <lizefan@...wei.com>
CC:	Linux Kernel Mailing List <Linux-Kernel@...r.Kernel.ORG>
Subject: Re: sched: RT throttling activated, 3.12.3

Li Zefan wrote:
> On 2013/12/11 10:59, Howard Chu wrote:
>> I just upgraded a system from a 3.5 kernel to 3.12.3 and attempted to run some new benchmarks on it. I see my test program ramps up in CPU usage for a few seconds and then it gradually tails off. There's nothing obvious in the user code to trigger this behavior, so I check dmesg, and see this:
>>
>> [   55.037057] JFS: nTxBlock = 8192, nTxLock = 65536
>> [163591.807470] perf samples too long (2758 > 2500), lowering kernel.perf_event_max_sample_rate to 50000
>> [164061.362762] perf samples too long (5204 > 5000), lowering kernel.perf_event_max_sample_rate to 25000
>> [167969.339513] [sched_delayed] sched: RT throttling activated
>> [182741.484637] perf samples too long (294588 > 10000), lowering kernel.perf_event_max_sample_rate to 12500
>> [182741.484726] INFO: NMI handler (perf_event_nmi_handler) took too long to run: 36.665 msecs
>> [182822.633084] perf samples too long (292359 > 20000), lowering kernel.perf_event_max_sample_rate to 6250
>> [182905.606119] perf samples too long (290291 > 40000), lowering kernel.perf_event_max_sample_rate to 3250
>> [199384.293514] perf samples too long (288142 > 76923), lowering kernel.perf_event_max_sample_rate to 1750
>> [208507.301027] perf samples too long (285964 > 142857), lowering kernel.perf_event_max_sample_rate to 1000
>> [208528.976208] perf samples too long (283799 > 250000), lowering kernel.perf_event_max_sample_rate to 500
>>
>> Why is the kernel throttling my server?
>>
>
> Because that is the default setting of the kernel.

Apparently a "new" default that didn't exist in 3.5? The code in question is 
not a realtime process. This behavior also wasn't seen in 3.10 or any older 
kernels.

> lxc34:/proc/sys/kernel # cat sched_rt_period_us
> 1000000
> lxc34:/proc/sys/kernel # cat sched_rt_runtime_us
> 950000
>
>


-- 
   -- Howard Chu
   CTO, Symas Corp.           http://www.symas.com
   Director, Highland Sun     http://highlandsun.com/hyc/
   Chief Architect, OpenLDAP  http://www.openldap.org/project/
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