From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:39478) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ao7p5-0003Lm-JK for qemu-devel@nongnu.org; Thu, 07 Apr 2016 07:10:04 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ao7p1-0000sA-DN for qemu-devel@nongnu.org; Thu, 07 Apr 2016 07:10:03 -0400 Received: from mx1.redhat.com ([209.132.183.28]:55472) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ao7p1-0000s5-7d for qemu-devel@nongnu.org; Thu, 07 Apr 2016 07:09:59 -0400 Date: Thu, 7 Apr 2016 12:09:52 +0100 From: "Dr. David Alan Gilbert" Message-ID: <20160407110951.GB2240@work-vm> References: <56445141.2070907@redhat.com> <5644561C.3060208@redhat.com> <56445FAB.80906@redhat.com> <87tworqwnk.fsf@emacs.mitica> <20151112195609.GD11416@work-vm> <5644F495.5050706@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5644F495.5050706@redhat.com> Subject: Re: [Qemu-devel] [v2 0/2] add avx2 instruction optimization List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Eric Blake Cc: "quintela@redhat.com" , "Li, Liang Z" , "qemu-devel@nongnu.org" , "mst@redhat.com" , "amit.shah@redhat.com" , Paolo Bonzini * Eric Blake (eblake@redhat.com) 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 / dgilbert@redhat.com / Manchester, UK