linux-kernel - Re: [BUG] scheduler doesn't balance thread to idle cpu for 3 seconds

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Message-ID: <20160128174903.GV6356@twins.programming.kicks-ass.net>
Date:	Thu, 28 Jan 2016 18:49:03 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Jan Stancek <jstancek@...hat.com>
Cc:	alex.shi@...el.com, guz.fnst@...fujitsu.com, mingo@...hat.com,
	jolsa@...hat.com, riel@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: [BUG] scheduler doesn't balance thread to idle cpu for 3 seconds

On Thu, Jan 28, 2016 at 04:55:02PM +0100, Jan Stancek wrote:
> On 01/27/2016 03:52 PM, Jan Stancek wrote:
> > Hello,
> > 
> > pthread_cond_wait_1/2 [1] is rarely failing for me on 4.5.0-rc1,
> > on x86_64 KVM guest with 2 CPUs.
> > 
> > This test [1]:
> > - spawns 2 SCHED_RR threads
> > - first thread with higher priority sets alarm for 2 seconds and blocks on condition
> > - second thread with lower priority is busy looping for 5 seconds
> > - after 2 seconds alarm signal arrives and handler signals condition
> > - high priority thread should resume running
> 
> I have slightly modified testcase, so it will finish immediately when high prio
> thread is done. And also to allow it to compile outside of openposix testsuite.

Yeah, I 'fixed' the testcase too.

So I've had it run for almost 2 hours without a single fail. I've
hot-plugged my cpu count down to 2.

How long should I have to wait for a fail?