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From:   Thomas Gleixner <tglx@linutronix.de>
To:     Andy Lutomirski <luto@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>
Cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        Mel Gorman <mgorman@suse.de>,
        LKML <linux-kernel@vger.kernel.org>,
        the arch/x86 maintainers <x86@kernel.org>,
        Christoph Hellwig <hch@lst.de>,
        Matthew Wilcox <willy@infradead.org>,
        Daniel Vetter <daniel@ffwll.ch>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linux-MM <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>,
        Steven Rostedt <rostedt@goodmis.org>,
        Ben Segall <bsegall@google.com>,
        Daniel Bristot de Oliveira <bristot@redhat.com>
Subject: Re: [patch V4 4/8] sched: Make migrate_disable/enable() independent of RT
In-Reply-To: <87mtz7n5ae.fsf@nanos.tec.linutronix.de>
References: <20201118194838.753436396@linutronix.de> <20201118204007.269943012@linutronix.de> <20201119093834.GH3306@suse.de> <20201119111411.GL3121378@hirez.programming.kicks-ass.net> <CAHk-=wire3dzhHx=KiL_f5Rj0=1u9ustsa33QoR-F9-v-NU9Ng@mail.gmail.com> <20201119182843.GA2414@hirez.programming.kicks-ass.net> <87tutkolq1.fsf@nanos.tec.linutronix.de> <20201120092928.GA3021@hirez.programming.kicks-ass.net> <CALCETrWHzHXLKuD4JWxDyBULAuFivP55csFp=6feireZhianVw@mail.gmail.com> <87mtz7n5ae.fsf@nanos.tec.linutronix.de>
Date:   Mon, 23 Nov 2020 22:25:24 +0100
Message-ID: <87h7pfn4u3.fsf@nanos.tec.linutronix.de>
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On Mon, Nov 23 2020 at 22:15, Thomas Gleixner wrote:
> On Sun, Nov 22 2020 at 15:16, Andy Lutomirski wrote:
>> On Fri, Nov 20, 2020 at 1:29 AM Peter Zijlstra <peterz@infradead.org> wrote:
>> The common case of a CPU switching back and forth between a small
>> number of mms would have no significant overhead.
>
> For CPUs which do not support PCID this sucks, which is everything pre
> Westmere and all of 32bit. Yes, 32bit. If we go there then 32bit has to
> bite the bullet and use the very same mechanism. Not that I care much
> TBH.

Bah, I completely forgot that AMD does not support PCID before Zen3
which is a major showstopper.

Thanks,

        tglx