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Groups > linux.kernel > #1250485

Re: Q: schedule() and implied barriers on arm64

From Peter Zijlstra <peterz@infradead.org>
Newsgroups linux.kernel
Subject Re: Q: schedule() and implied barriers on arm64
Date 2015-10-19 11:10 +0200
Message-ID <qleC7-8fX-27@gated-at.bofh.it> (permalink)
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On Mon, Oct 19, 2015 at 09:06:05AM +0200, Ingo Molnar wrote:
> 
> * Peter Zijlstra <peterz@infradead.org> wrote:
> 
> > In any case, its all moot now, since Paul no longer requires schedule() to imply 
> > a full barrier.
> >
> > [...]
> 
> Nevertheless from a least-surprise POV it might be worth guaranteeing it, because 
> I bet there's tons of code that assumes that schedule() is a heavy operation and 
> it's such an easy mistake to make. Since we are so close to having that guarantee, 
> we might as well codify it?
> 
> Just like system calls are assumed to be barriers in general - 

Are they? I know they are on some platforms, but I'm not sure we've
audited them all and established this.

> and system calls are more lightweight than schedule() ...

Hopefully, although if you enable nohz_full there's a fair chance to
reverse that :-)
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Thread

Q: schedule() and implied barriers on arm64 Peter Zijlstra <peterz@infradead.org> - 2015-10-16 17:20 +0200
  Re: Q: schedule() and implied barriers on arm64 "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-10-16 18:10 +0200
    Re: Q: schedule() and implied barriers on arm64 Peter Zijlstra <peterz@infradead.org> - 2015-10-16 18:20 +0200
      Re: Q: schedule() and implied barriers on arm64 "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-10-16 18:40 +0200
        Re: Q: schedule() and implied barriers on arm64 Peter Zijlstra <peterz@infradead.org> - 2015-10-16 18:40 +0200
      Re: Q: schedule() and implied barriers on arm64 Catalin Marinas <catalin.marinas@arm.com> - 2015-10-16 19:00 +0200
        Re: Q: schedule() and implied barriers on arm64 "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-10-16 19:30 +0200
          Re: Q: schedule() and implied barriers on arm64 Peter Zijlstra <peterz@infradead.org> - 2015-10-16 21:10 +0200
            Re: Q: schedule() and implied barriers on arm64 "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-10-16 21:30 +0200
          Re: Q: schedule() and implied barriers on arm64 Catalin Marinas <catalin.marinas@arm.com> - 2015-10-19 17:20 +0200
        Re: Q: schedule() and implied barriers on arm64 Peter Zijlstra <peterz@infradead.org> - 2015-10-16 21:10 +0200
          Re: Q: schedule() and implied barriers on arm64 Ingo Molnar <mingo@kernel.org> - 2015-10-19 09:10 +0200
            Re: Q: schedule() and implied barriers on arm64 Peter Zijlstra <peterz@infradead.org> - 2015-10-19 11:10 +0200
            Re: Q: schedule() and implied barriers on arm64 Catalin Marinas <catalin.marinas@arm.com> - 2015-10-19 17:30 +0200
              Re: Q: schedule() and implied barriers on arm64 Peter Zijlstra <peterz@infradead.org> - 2015-10-19 18:30 +0200
                Re: Q: schedule() and implied barriers on arm64 Ingo Molnar <mingo@kernel.org> - 2015-10-20 10:40 +0200
                Re: Q: schedule() and implied barriers on arm64 Will Deacon <will.deacon@arm.com> - 2015-10-27 17:30 +0100
                Re: Q: schedule() and implied barriers on arm64 Peter Zijlstra <peterz@infradead.org> - 2015-10-28 01:20 +0100
                Re: Q: schedule() and implied barriers on arm64 Will Deacon <will.deacon@arm.com> - 2015-10-28 11:50 +0100
    Re: Q: schedule() and implied barriers on arm64 Catalin Marinas <catalin.marinas@arm.com> - 2015-10-16 19:20 +0200

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