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Date: Sun, 9 Jul 2017 17:20:20 -0400
From: "Emilio G. Cota" <cota@braap.org>
Message-ID: <20170709212020.GA2834@flamenco>
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Subject: Re: [Qemu-devel] [PATCH 03/22] cputlb: bring back tlb_flush_count
 under !TLB_DEBUG
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To: Richard Henderson <rth@twiddle.net>
Cc: qemu-devel@nongnu.org

On Sun, Jul 09, 2017 at 16:56:23 -0400, Emilio G. Cota wrote:
> On Sun, Jul 09, 2017 at 10:00:01 -1000, Richard Henderson wrote:
> > On 07/08/2017 09:49 PM, Emilio G. Cota wrote:
> > >+    atomic_set(&env->tlb_flush_count, env->tlb_flush_count + 1);
> > 
> > Want atomic_read here, so they're all the same.
> 
> It's not needed. Note that this thread is the only one ever writing
> to env->tlb_flush_count, so the thread can read this value without
> atomic accesses.
> 
> You'll see this pattern all across the patchset.

We already have this kind of pattern in QEMU. See this patch and
related discussion:
  https://patchwork.kernel.org/patch/9358939/

		E.