linux-kernel - Re: [GIT PULL] scheduler updates for v4.15

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Date:   Mon, 13 Nov 2017 16:13:28 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Mike Galbraith <efault@....de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-kernel@...r.kernel.org,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [GIT PULL] scheduler updates for v4.15


* Mike Galbraith <efault@....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