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

[Li, Liang Z]

> On 12/11/2015 10:40, Li, Liang Z wrote:
> > I migrate a 8GB RAM Idle guest,  I think most of it's pages are zero pages.
> >
> > I use your new code:
> > -------------------------------------------------
> >     unsigned long *p = ...
> >     if (p[0] || p[1] || p[2] || p[3]
> >         || memcmp(p+4, p, size - 4 * sizeof(unsigned long)) != 0)
> >             return BUFFER_NOT_ZERO;
> >     else
> >             return BUFFER_ZERO;
> > ---------------------------------------------------
> > and the result is almost the same.  I also tried the check 8, 16 long
> > data at the beginning, same result.
> 
> Interesting...  Well, all I can say is that applaud you for testing your 
> hypothesis
> with the benchmark.
> 
> Probably the setup cost of memcmp is too high, because the testing loop is
> already very optimized.
> 
> Please submit the AVX2 version if it helps!

Yes, the AVX2 version really helps. I have already submitted it, could you help 
to review it?

I am curious about the original intention to add the SSE2 Intrinsics, is the 
same reason?

I even suspect the VM may impact the 'memcmp()' performance, is it possible?

Liang

> Paolo