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

[Dr. David Alan Gilbert]

* Eric Blake (address@hidden) wrote:
> On 11/12/2015 12:56 PM, Dr. David Alan Gilbert wrote:
> 
> >> One thing I still can't understand, why the unit test in host environment 
> >> shows
> >> 'memcmp()' have better performance?
> 
> Have you tried running under a profiler, to see if there are hotspots or
> at least get an idea of where the time is being spent?
> 
> > 
> > Are you aware of any program other than QEMU that also wants to do something
> > similar?  Finding whether a block of memory is zero, sounds like something
> > that would be useful in lots of places, I just can't think which ones.
> 
> At least dd, cp, and probably several other utilities.  It would be nice
> to post an RFE to glibc to see if they can come up with a dedicated
> interface that is faster than memcmp(), although that still only helps
> us when targetting a system new enough to have that interface.

I've just posted that RFE:
https://sourceware.org/bugzilla/show_bug.cgi?id=19920

Dave

> -- 
> Eric Blake   eblake redhat com    +1-919-301-3266
> Libvirt virtualization library http://libvirt.org
> 


--
Dr. David Alan Gilbert / address@hidden / Manchester, UK