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Re: [Qemu-devel] [PATCH] tcg: Remove stack protection from helper functi

From: Laurent Desnogues
Subject: Re: [Qemu-devel] [PATCH] tcg: Remove stack protection from helper functions
Date: Mon, 26 Sep 2011 10:15:06 +0200

On Mon, Sep 26, 2011 at 10:01 AM, Mulyadi Santosa
<address@hidden> wrote:
> Hi...
> On Mon, Sep 26, 2011 at 14:46, Jan Kiszka <address@hidden> wrote:
>> This increases the overhead of frequently executed helpers.
>> Signed-off-by: Jan Kiszka <address@hidden>
> IMHO, stack protector setup put more stuffs during epilogue, but quite
> likely it is negligible unless it cause too much L1 cache misses. So,
> I think this micro tuning is somewhat unnecessary but still okay.

The impact of stack protection is very high for instance running
FFmpeg ARM with NEON optimizations:  a few months ago I
measured that removing stack protection improved the run time
by more than 10%.  Of course it's extreme since the proportion
of NEON instructions (and hence of helper calls) is very high.


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