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Date: Mon, 13 Nov 2017 16:13:28 +0100
From: Ingo Molnar <mingo@kernel.org>
To: Mike Galbraith <efault@gmx.de>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
        linux-kernel@vger.kernel.org, Peter Zijlstra <a.p.zijlstra@chello.nl>,
        Thomas Gleixner <tglx@linutronix.de>,
        Andrew Morton <akpm@linux-foundation.org>,
        Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [GIT PULL] scheduler updates for v4.15
Message-ID: <20171113151328.qwufqpvexevfjl4u@gmail.com>
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* Mike Galbraith <efault@gmx.de> wrote:

> On Mon, 2017-11-13 at 09:00 +0100, Ingo Molnar wrote:
> > 
> >  - Improve the RT IPI based balancing logic (Steven Rostedt)
> 
> Well how 'bout that, serendipity strikes again:
> 
> I just got a report that a proggy Gregory Haskins wrote back in 2007
> (preempt-test) was claiming RT was broken, but no, it's every kernel
> containing b6366f048e0c.  What the proggy does is to start a gaggle of
> RT tasks of descending priority, giving each an identical quantum of
> work to do, expecting higher priority tasks to get it done before
> lower.  That currently does not always happen, we occasionally do not
> get a task pushed for long enough that a task that should have been
> preempted by a push shortly after hitting the CPU, manages to remain
> long enough to finish well before it should have been able to.
> 
> This patch fixed it up before I could even get my troubleshooting
> wheels properly smoking (they spin a bit before getting traction).
>  Given that, not to mention b6366f048e0c being capable of log jamming
> even fairly modest boxen, perhaps this patch wants a stable tag?

Ok, agreed - I've forwarded 4bdced5c9a29 to Greg for -stable inclusion.

Thanks,

	Ingo