From: Dietmar Eggemann <firstname.lastname@example.org> To: Peter Zijlstra <email@example.com>, Ley Foon Tan <firstname.lastname@example.org> Cc: Vincent Guittot <email@example.com>, Ingo Molnar <firstname.lastname@example.org>, Greg KH <email@example.com>, firstname.lastname@example.org, Quentin Perret <email@example.com> Subject: Re: sched: Question about big and little cores system with SMP and EAS Date: Wed, 16 Jun 2021 15:20:30 +0200 [thread overview] Message-ID: <firstname.lastname@example.org> (raw) In-Reply-To: <YMni2eclmqf05cL4@hirez.programming.kicks-ass.net> - Quentin Perret <email@example.com> + Quentin Perret <firstname.lastname@example.org> On 16/06/2021 13:39, Peter Zijlstra wrote: > On Wed, Jun 16, 2021 at 07:29:26PM +0800, Ley Foon Tan wrote: >> Hi all >> >> Would like to ask the experts here regarding the Symmetric >> Multi-Processing mode (SMP) with Energy aware scheduler (EAS) support >> on the big + little cores system. > > And the you ask a question unrelated to either Symmetric MP or EAS :-) > >> Hardware system: >> Big and little cores have almost the same ISA, but the big core has >> some extension instructions that little core doesn't have. > > That problem is unrelated to big.Little / EAS, also by definition that > is not SMP seeing how the 'S' is a blatant lie. > > The simplest solution is to simply disallow usage of the extended ISA > and force mandate the common subset. The complicated answer is something > along the lines of: > > https://email@example.com We don't encourage asymmetric ISA extensions for EAS*/CAS** on big.Little systems. It would be simply a nightmare to schedule tasks on such systems. The exception to this is the 'asymmetric 32-bit Soc' to support 32bit legacy Apps. The nightmare for scheduling is reduced in this case to CPU affinity, something the task scheduler has to live with already today. (+ DL admission control for 32bit tasks). * Documentation/scheduler/sched-energy.rst ** Documentation/scheduler/sched-capacity.rst
next prev parent reply other threads:[~2021-06-16 13:20 UTC|newest] Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-06-16 11:29 Ley Foon Tan 2021-06-16 11:39 ` Peter Zijlstra 2021-06-16 13:20 ` Dietmar Eggemann [this message] 2021-06-17 5:00 ` Ley Foon Tan 2021-06-17 7:51 ` Morten Rasmussen
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