Re: [PATCH v4 10/10] x86/mm: Try to preserve old TLB entries using PCID

From	Ingo Molnar <mingo@kernel.org>
Newsgroups	linux.kernel
Subject	Re: [PATCH v4 10/10] x86/mm: Try to preserve old TLB entries using PCID
Date	2017-07-18 11:00 +0200
Message-ID	<u4wwj-9E-49@gated-at.bofh.it> (permalink)
References	<tXK1k-11t-7@gated-at.bofh.it> <tXK1l-11t-9@gated-at.bofh.it> <tZRrI-67q-17@gated-at.bofh.it> <tZV2j-8vO-51@gated-at.bofh.it> <tZVYm-Ge-9@gated-at.bofh.it>
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* Peter Zijlstra <peterz@infradead.org> wrote:

> On Wed, Jul 05, 2017 at 09:04:39AM -0700, Andy Lutomirski wrote:
> > On Wed, Jul 5, 2017 at 5:18 AM, Peter Zijlstra <peterz@infradead.org> wrote:
> > > On Thu, Jun 29, 2017 at 08:53:22AM -0700, Andy Lutomirski wrote:
> > >> @@ -104,18 +140,20 @@ void switch_mm_irqs_off(struct mm_struct *prev, struct mm_struct *next,
> > >>
> > >>               /* Resume remote flushes and then read tlb_gen. */
> > >>               cpumask_set_cpu(cpu, mm_cpumask(next));
> > >
> > > Barriers should have a comment... what is being ordered here against
> > > what?
> > 
> > How's this comment?
> > 
> >         /*
> >          * Resume remote flushes and then read tlb_gen.  We need to do
> >          * it in this order: any inc_mm_tlb_gen() caller that writes a
> >          * larger tlb_gen than we read here must see our cpu set in
> >          * mm_cpumask() so that it will know to flush us.  The barrier
> >          * here synchronizes with inc_mm_tlb_gen().
> >          */
> 
> Slightly confusing, you mean this, right?
> 
> 
> 	cpumask_set_cpu(cpu, mm_cpumask());			inc_mm_tlb_gen();
> 
> 	MB							MB
> 
> 	next_tlb_gen = atomic64_read(&next->context.tlb_gen);	flush_tlb_others(mm_cpumask());
> 
> 
> which seems to make sense.

Btw., I'll wait for a v5 iteration before applying this last patch to tip:x86/mm.

Thanks,

	Ingo

Thread

Re: [PATCH v4 10/10] x86/mm: Try to preserve old TLB entries using  PCID Peter Zijlstra <peterz@infradead.org> - 2017-07-05 14:20 +0200
  Re: [PATCH v4 10/10] x86/mm: Try to preserve old TLB entries using PCID Andy Lutomirski <luto@kernel.org> - 2017-07-05 18:10 +0200
    Re: [PATCH v4 10/10] x86/mm: Try to preserve old TLB entries using  PCID Peter Zijlstra <peterz@infradead.org> - 2017-07-05 19:10 +0200
      Re: [PATCH v4 10/10] x86/mm: Try to preserve old TLB entries using  PCID Ingo Molnar <mingo@kernel.org> - 2017-07-18 11:00 +0200
        Re: [PATCH v4 10/10] x86/mm: Try to preserve old TLB entries using PCID Andy Lutomirski <luto@kernel.org> - 2017-07-18 19:10 +0200

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