linux-kernel - Re: RFC: futex_wait() can DoS the tick

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Message-ID: <20150610151551.3cfc616a@gandalf.local.home>
Date:	Wed, 10 Jun 2015 15:15:51 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Mike Galbraith <umgwanakikbuti@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: RFC: futex_wait() can DoS the tick

On Wed, 10 Jun 2015 20:59:49 +0200 (CEST)
Thomas Gleixner <tglx@...utronix.de> wrote:

> On Wed, 10 Jun 2015, Mike Galbraith wrote:
> 
> > On Wed, 2015-06-10 at 17:12 +0200, Thomas Gleixner wrote:
> > 
> > > Some more information about your symptoms in form of configuration,
> > > extra patches, kernel traces etc. would be appreciated.
> > 
> > homer:~/tmp # perf record -C 3 -eirq:*,irq_vectors:local* -- sleep 10

I would recommend using trace-cmd especially if you add function
tracing, as it's made more for fast tracing.

-- Steve

> > [ perf record: Woken up 2 times to write data ]
> > [ perf record: Captured and wrote 1380.507 MB perf.data (19530595 samples) ]
> > homer:~/tmp # perf script | grep irq_vectors:local_timer
> >      ksoftirqd/3    19 [003]  5586.564238: irq_vectors:local_timer_entry: vector=239
> >      ksoftirqd/3    19 [003]  5586.564239: irq_vectors:local_timer_exit: vector=239
> >      ksoftirqd/3    19 [003]  5586.568238: irq_vectors:local_timer_entry: vector=239
> >      ksoftirqd/3    19 [003]  5586.568239: irq_vectors:local_timer_exit: vector=239
> >      ksoftirqd/3    19 [003]  5586.632218: irq_vectors:local_timer_entry: vector=239
> 
> That gap is odd. Can you fire up the function tracer please?
> 
> Thanks,
> 
> 	tglx

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