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

[Juan Quintela <quintela@redhat.com>]

"Li, Liang Z" <liang.z.li@intel.com> wrote:
>> 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!

I read the email in the wrong order.  Forget about my other email.

Sorry, Juan.


>
> 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