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([2601:646:c200:1ef2:5066:c8ba:b185:db28]) by smtp.gmail.com with ESMTPSA id m8sm11328937pgg.1.2020.11.23.14.07.21 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 23 Nov 2020 14:07:21 -0800 (PST) Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable From: Andy Lutomirski Mime-Version: 1.0 (1.0) Subject: Re: [patch V4 4/8] sched: Make migrate_disable/enable() independent of RT Date: Mon, 23 Nov 2020 14:07:19 -0800 Message-Id: <9BAD6F21-4DB5-4277-A38D-BB1FA038F2D7@amacapital.net> References: <87h7pfn4u3.fsf@nanos.tec.linutronix.de> Cc: Andy Lutomirski , Peter Zijlstra , Linus Torvalds , Mel Gorman , LKML , the arch/x86 maintainers , Christoph Hellwig , Matthew Wilcox , Daniel Vetter , Andrew Morton , Linux-MM , Ingo Molnar , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Daniel Bristot de Oliveira In-Reply-To: <87h7pfn4u3.fsf@nanos.tec.linutronix.de> To: Thomas Gleixner X-Mailer: iPhone Mail (18B92) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > On Nov 23, 2020, at 1:25 PM, Thomas Gleixner wrote: >=20 > =EF=BB=BFOn 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 w= rote: >>> The common case of a CPU switching back and forth between a small >>> number of mms would have no significant overhead. >>=20 >> 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. >=20 > Bah, I completely forgot that AMD does not support PCID before Zen3 > which is a major showstopper. Why? Couldn=E2=80=99t we rig up the code so we still track all the ASIDs ev= en if there is no CPU support? We would take the TLB flush hit on every con= text switch, but we pay that cost anyway. We would avoid the extra copy in t= he same cases in which we would avoid it if we had PCID. >=20 > Thanks, >=20 > tglx