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

From: Avi Kivity
Subject: Re: [Qemu-devel] [PATCH] tcg: Remove stack protection from helper functions
Date: Mon, 26 Sep 2011 20:41:24 +0300
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:6.0.2) Gecko/20110906 Thunderbird/6.0.2

On 09/26/2011 11:15 AM, Laurent Desnogues wrote:
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.

I saw a lot of helper calls for sse in ordinary x86_64 code, likely for memcpy/cmp and friends. Native tcg ops for common vector instructions would probably be quite a speedup.

error compiling committee.c: too many arguments to function

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