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Date:   Thu, 19 Nov 2020 09:17:02 -0500
From:   Steven Rostedt <rostedt@goodmis.org>
To:     Mel Gorman <mgorman@suse.de>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        LKML <linux-kernel@vger.kernel.org>, x86@kernel.org,
        Linus Torvalds <torvalds@linuxfoundation.org>,
        Christoph Hellwig <hch@lst.de>,
        Matthew Wilcox <willy@infradead.org>,
        Daniel Vetter <daniel@ffwll.ch>,
        Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org,
        Ingo Molnar <mingo@kernel.org>,
        Juri Lelli <juri.lelli@redhat.com>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Ben Segall <bsegall@google.com>,
        Daniel Bristot de Oliveira <bristot@redhat.com>,
        Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [patch V4 4/8] sched: Make migrate_disable/enable() independent
 of RT
Message-ID: <20201119091702.59aac061@gandalf.local.home>
In-Reply-To: <20201119121413.GI3306@suse.de>
References: <20201118194838.753436396@linutronix.de>
        <20201118204007.269943012@linutronix.de>
        <20201119093834.GH3306@suse.de>
        <20201119111411.GL3121378@hirez.programming.kicks-ass.net>
        <20201119121413.GI3306@suse.de>
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On Thu, 19 Nov 2020 12:14:13 +0000
Mel Gorman <mgorman@suse.de> wrote:

> * Usage of migrate_disable is heavily discouraged as it is extremely
> * hazardous on PREEMPT_RT kernels and any usage needs to be heavily

I don't believe it's just PREEMPT_RT. It's RT tasks that are concerned,
especially when you are dealing with SCHED_DEADLINE.

PREEMPT_RT just allows better determinism for RT tasks, but the issue with
migrate_disable is not limited to just PREEMPT_RT.

-- Steve


> * justified. Before even thinking about using this, read
> * "Migrate-Disable and why it is undesired" in
> * include/linux/preempt.h and include both a comment and document
> * in the changelog why the use case is an exception.