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Date: Thu, 25 Feb 2016 15:06:27 +0100 From: Sebastian Andrzej Siewior <bigeasy@...utronix.de> To: Tim Sander <tim@...eglstein.org> Cc: linux-rt-users <linux-rt-users@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>, Thomas Gleixner <tglx@...utronix.de>, rostedt@...dmis.org, John Kacur <jkacur@...hat.com> Subject: Re: Bisect results for 4.4.1-rt[4,5] On 02/17/2016 09:14 AM, Tim Sander wrote: > Hi Sebastian Hi Tim, > I have done a bisect run, its a rather innocent looking on liner which seems > to cause the problems. The numbers where reasonably stable so i am pretty > confident that this is the patch giving ~26µs additional latency on the Altera > SOC plattform: > > eec2bf477ac674583a7d73b9d00f47c528b7266d is the first bad commit > commit eec2bf477ac674583a7d73b9d00f47c528b7266d > Author: Sebastian Andrzej Siewior <bigeasy@...utronix.de> > Date: Thu Feb 4 16:38:10 2016 +0100 > > kernel/perf: mark perf_cpu_context's timer as irqsafe > > Otherwise we get a WARN_ON() backtrace and some events are reported as > "not counted". > > Cc: stable-rt@...r.kernel.org > Reported-by: Yang Shi <yang.shi@...aro.org> > Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de> Seriously? That patch? I played a little and I doubt seriously that this patch has something to do with it. So before that patch you would have a warn_on spotted and complained if that timer would fire. So that is one reason why I doubt that this patch is in charge of the 25us. If I add a printk() to that timer I don't see it under "normal" circumstances. However I do perf_4.3 stat -e branches,branch-misses,bus-cycles,cache-misses,cache-references,cycles,instructions apt-get update then I see them fire. > Best Regards > Tim Sebastian
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