Groups > linux.kernel > #1198863

Re: [PATCH 05/10] nohz: New tick dependency mask

From	Frederic Weisbecker <fweisbec@gmail.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH 05/10] nohz: New tick dependency mask
Date	2015-08-03 16:00 +0200
Message-ID	<pTorw-4RW-3@gated-at.bofh.it> (permalink)
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On Mon, Aug 03, 2015 at 03:29:58PM +0200, Peter Zijlstra wrote:
> On Mon, Aug 03, 2015 at 03:09:39PM +0200, Frederic Weisbecker wrote:
> 
> > > That doesn't make any sense:
> > > 
> > >   tick_nohz_set_tick_dependency_this_cpu();
> > > 
> > > (shees, you're nowhere near lazy enough, that's insane to type) is
> > > almost identical to:
> > > 
> > >   tick_nohz_set_tick_dependency_cpu(.cpu = smp_processor_id());
> > > 
> > > The only difference is a _very_ slight reduction in cost for computing
> > > the per-cpu offset.
> > 
> > But the local one must be NMI-safe. Now I can do:
> > 
> >     if (cpu == smp_processor_id())
> >         tick_nohz_full_kick() // NMI-safe
> >     else
> >         tick_nohz_full_kick_cpu(cpu); // not NMI-safe.
> 
> Urgh, I missed that. But yes, I suppose that's ok seeing how we result
> in a smaller interface.
> 
> I was going to say that with a bit of luck GCC could optimize it, but
> its not inline so no it cannot.

I might inline all these set_dep() things to introduce static keys on these
APIs.. But the kick itself will remain real calls.

Ok how about tick_nohz_set_dep_nmi() so that we know exactly what's the purpose
here. Still a long function name but it's clear.
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Thread

Re: [PATCH 05/10] nohz: New tick dependency mask Peter Zijlstra <peterz@infradead.org> - 2015-08-03 15:00 +0200
  Re: [PATCH 05/10] nohz: New tick dependency mask Frederic Weisbecker <fweisbec@gmail.com> - 2015-08-03 15:10 +0200
    Re: [PATCH 05/10] nohz: New tick dependency mask Peter Zijlstra <peterz@infradead.org> - 2015-08-03 15:40 +0200
      Re: [PATCH 05/10] nohz: New tick dependency mask Frederic Weisbecker <fweisbec@gmail.com> - 2015-08-03 16:00 +0200
        Re: [PATCH 05/10] nohz: New tick dependency mask Peter Zijlstra <peterz@infradead.org> - 2015-08-03 16:20 +0200

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