Re: [Qemu-devel] [v2 0/2] add avx2 instruction optimization

[Li, Liang Z]

> Rather than trying to cater to multiple assembly instruction implementations
> ourselves, have you tried taking the ideas in this earlier thread?
> https://lists.gnu.org/archive/html/qemu-devel/2015-10/msg05298.html
> 
> Ideally, libc's memcmp() will already be using the most efficient assembly
> instructions without us having to reproduce the work of picking the 
> instructions
> that work best.
> 

Eric, thanks for you information. I didn't notice that discussion before.


I rewrite the buffer_find_nonzero_offset() with the 'bool memeqzero4_paolo 
length'
then write a test program to check a large amount of zero pages,  and use the 
'time' to 
recode the time takes by different optimization. Test result is like this:

SSE2:
------------------------------------------------------
              |            test 1         |     test 2
----------------------------------------------------
Time(S):|       13.696            | 13.533  
------------------------------------------------


AVX2:
-------------------------------------------
              |        test 1     | test 2
-------------------------------------------
Time (S):|      10.583      |  10.306
-------------------------------------------

memeqzero4_paolo:
---------------------------------------
              |        test 1     | test 2
---------------------------------------
Time (S):|      9.718     |  9.817
----------------------------------------


Paolo's implementation has the best performance. It seems that we can remove 
the SSE2 related Intrinsics.

Liang
> --
> Eric Blake   eblake redhat com    +1-919-301-3266
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