Re: [PATCH v2 18/19] ARC: [plat-eznps] replace sync with proper cpu barrier

From	Peter Zijlstra <peterz@infradead.org>
Newsgroups	linux.kernel
Subject	Re: [PATCH v2 18/19] ARC: [plat-eznps] replace sync with proper cpu barrier
Date	2015-11-17 12:30 +0100
Message-ID	<qvMCt-4n1-13@gated-at.bofh.it> (permalink)
References	<qpEeC-3hu-3@gated-at.bofh.it> <qvMsO-4ho-5@gated-at.bofh.it> <qvMsO-4ho-3@gated-at.bofh.it>
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On Tue, Nov 17, 2015 at 04:42:49PM +0530, Vineet Gupta wrote:
> On Saturday 07 November 2015 04:22 PM, Noam Camus wrote:
> > From: Tal Zilcer <talz@ezchip.com>
> > 
> > In SMT system like we have the generic "sync" is not working with
> > HW threads. The replacement is "schd.rw" instruction that is served
> > as cpu barrier for HW threads.
> 
> As discussed in v2 of this patch, SYNC or some such in __switch_to is completely
> superfluous. We don't need this patch, you may instead wanna submit a patch which
> removes the sync. Also please do that in assembler version of this file as well !

Do test it though; as is ARC-SMP seems to have a _lot_ of superfluous
barriers many of which have no explanation yet (I'm thinking of those
extra smp_mb()s in the lock primitives).
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Thread

Re: [PATCH v2 18/19] ARC: [plat-eznps] replace sync with proper cpu  barrier Vineet Gupta <Vineet.Gupta1@synopsys.com> - 2015-11-17 12:20 +0100
  Re: [PATCH v2 18/19] ARC: [plat-eznps] replace sync with proper cpu  barrier Peter Zijlstra <peterz@infradead.org> - 2015-11-17 12:30 +0100
    Re: [PATCH v2 18/19] ARC: [plat-eznps] replace sync with proper cpu  barrier Vineet Gupta <Vineet.Gupta1@synopsys.com> - 2015-11-17 12:40 +0100
      Re: [PATCH v2 18/19] ARC: [plat-eznps] replace sync with proper cpu  barrier Peter Zijlstra <peterz@infradead.org> - 2015-11-17 13:30 +0100
        Re: [PATCH v2 18/19] ARC: [plat-eznps] replace sync with proper cpu  barrier Vineet Gupta <Vineet.Gupta1@synopsys.com> - 2015-11-17 13:40 +0100
          Re: [PATCH v2 18/19] ARC: [plat-eznps] replace sync with proper cpu  barrier Peter Zijlstra <peterz@infradead.org> - 2015-11-17 13:50 +0100
            Re: [PATCH v2 18/19] ARC: [plat-eznps] replace sync with proper cpu  barrier Vineet Gupta <Vineet.Gupta1@synopsys.com> - 2015-11-17 14:40 +0100
              Re: [PATCH v2 18/19] ARC: [plat-eznps] replace sync with proper cpu  barrier Peter Zijlstra <peterz@infradead.org> - 2015-11-17 15:00 +0100

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