Re: [Qemu-devel] [PATCH v3 0/9] Improve buffer_is_zero

[Paolo Bonzini]

On 29/08/2016 20:46, Richard Henderson wrote:
> Changes from v2 to v3:
> 
>   * Unit testing.  This includes having x86 attempt all versions of
>     the accelerator that will run on the hardware.  Thus an avx2 host
>     will run the basic test 5 times (1.5sec on my laptop).
> 
>   * Drop the ppc and aarch64 specializations.  I have improved the
>     basic integer version to the point that those vectorized versions
>     are not a win.
> 
>     In the case of my aarch64 mustang, the integer version is 4 times
>     faster than the neon version that I delete.  With effort I was
>     able to rewrite the neon version to come to within a factor of 1.1,
>     but it remained slower than the integer.  To be fair, gcc6 makes
>     very good use of ldp, so the integer path is *also* loading 16 bytes
>     per insn.
> 
>     I can forward my standalone aarch64 benchmark if anyone is interested.
> 
>     Note however that at least the avx2 acceleration is still very much
>     a win, being about 3 times faster on my laptop.  Of course, it's
>     handling 4 times as much data per loop as the integer version, so
>     one can still see the overhead caused by using vector insns.
> 
>     For grins I wrote an avx512 version, if someone has a skylake upon
>     which to test and benchmark.  That requires additional configure
>     checks, so I didn't bother to include it here.

Thanks, queued for 2.8.

Paolo