linux-kernel - sched: RT throttling activated, 3.12.3

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Date:	Tue, 10 Dec 2013 18:59:30 -0800
From:	Howard Chu <hyc@...as.com>
To:	Linux Kernel Mailing List <Linux-Kernel@...r.Kernel.ORG>
Subject: sched: RT throttling activated, 3.12.3

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?

-- 
   -- 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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