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From: Qais Yousef <qais.yousef@arm.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: mingo@kernel.org, linux-kernel@vger.kernel.org,
	Geert Uytterhoeven <geert@linux-m68k.org>,
	Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH 0/5] Fix FIFO-99 abuse
Date: Fri, 2 Aug 2019 16:21:58 +0100	[thread overview]
Message-ID: <20190802152157.7fp775lg7tbm5rec@e107158-lin.cambridge.arm.com> (raw)
In-Reply-To: <20190802143324.GH2332@hirez.programming.kicks-ass.net>

On 08/02/19 16:33, Peter Zijlstra wrote:
> > > Also also, RR-SMP is actually broken (and nobody has cared enough to
> > > bother fixing it).
> > 
> > If you can give me enough pointers to understand the problem I might be able to
> > bother with it :-)
> 
> So the push-pull balancer we have (designed for FIFO but also applied to
> RR) will only move a task if the destination CPU has a lower prio.  In
> the case where one CPU has 3 tasks and the other 1, and they're all the
> same prio, it does nothing.  For FIFO that is fine, for RR, not so much.
> 
> Because then the one CPU will RR between 3 tasks, giving each task
> 1/3rd, while the other will only run the one task.

Okay so what we need to do is keep a count of number of RR tasks on each CPU
(which we already do IIRC) and take that into account in
find_loweset_rq()/cpupri_find().

Let me see if I can create a test case then hack something.

Thanks

--
Qais Yousef

      reply	other threads:[~2019-08-02 15:22 UTC|newest]

Thread overview: 37+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-01 11:13 [PATCH 0/5] Fix FIFO-99 abuse Peter Zijlstra
2019-08-01 11:13 ` [PATCH 1/5] sched/pci: Reduce psimon FIFO priority Peter Zijlstra
2019-08-01 17:49   ` Johannes Weiner
2019-08-01 18:31     ` Suren Baghdasaryan
2019-08-01 21:03       ` Suren Baghdasaryan
2019-08-01 21:02     ` Peter Zijlstra
2019-08-01 11:13 ` [PATCH 2/5] rcu/tree: Fix SCHED_FIFO params Peter Zijlstra
2019-08-01 13:51   ` Paul E. McKenney
2019-08-01 14:43     ` Peter Zijlstra
2019-08-01 15:33       ` Paul E. McKenney
2019-08-01 11:13 ` [PATCH 3/5] crypto: Reduce default RT priority Peter Zijlstra
2019-08-09  6:19   ` Herbert Xu
2019-08-01 11:13 ` [PATCH 4/5] media/ivtv: Reduce default FIFO priority Peter Zijlstra
2019-08-01 12:24   ` Andy Walls
2019-08-01 12:38     ` Peter Zijlstra
2019-08-02  8:58       ` Peter Zijlstra
2019-08-07  9:26         ` Hans Verkuil
2019-08-01 11:13 ` [PATCH 5/5] spi: Reduce kthread priority Peter Zijlstra
2019-08-01 11:26   ` Mark Brown
2019-08-01 12:07     ` Peter Zijlstra
2019-08-01 11:27   ` Geert Uytterhoeven
2019-08-01 12:12     ` Peter Zijlstra
2019-08-01 12:16       ` Geert Uytterhoeven
2019-08-01 11:27   ` Enric Balletbo i Serra
2019-08-01 12:17     ` Peter Zijlstra
2019-08-01 12:35       ` Mark Brown
2019-08-01 15:44         ` Doug Anderson
2019-08-02 11:22   ` Applied "spi: Reduce kthread priority" to the spi tree Mark Brown
2019-08-02 11:22     ` Mark Brown
2019-08-01 13:17 ` [PATCH 0/5] Fix FIFO-99 abuse Qais Yousef
2019-08-02  9:32   ` Peter Zijlstra
2019-08-02  9:50     ` Thomas Gleixner
2019-08-02 10:26     ` Qais Yousef
2019-08-02 12:41       ` Peter Zijlstra
2019-08-02 14:08         ` Qais Yousef
2019-08-02 14:33           ` Peter Zijlstra
2019-08-02 15:21             ` Qais Yousef [this message]

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