From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:49157) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Ub49a-0000ny-1D for qemu-devel@nongnu.org; Sat, 11 May 2013 03:23:39 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Ub49X-0007LP-Hg for qemu-devel@nongnu.org; Sat, 11 May 2013 03:23:37 -0400 Received: from hall.aurel32.net ([2001:470:1f15:c4f::1]:43960) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Ub49X-0007J1-B2 for qemu-devel@nongnu.org; Sat, 11 May 2013 03:23:35 -0400 Date: Sat, 11 May 2013 09:23:32 +0200 From: Aurelien Jarno Message-ID: <20130511072332.GF19954@ohm.aurel32.net> References: <1368188203-3407-1-git-send-email-pbonzini@redhat.com> <874nebdm4r.fsf@codemonkey.ws> <518CF130.2030402@redhat.com> <518CF4C4.6020901@suse.de> <518CF669.30803@redhat.com> <871u9ezypj.fsf@codemonkey.ws> <518D0B68.505@redhat.com> <87ip2q91ho.fsf@codemonkey.ws> <518D5FAA.5050507@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <518D5FAA.5050507@redhat.com> Subject: Re: [Qemu-devel] [PATCH for-1.5 0/9] Disable expensive QOM cast debugging for official releases List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Paolo Bonzini Cc: Anthony Liguori , mst@redhat.com, qemu-devel@nongnu.org, Andreas =?iso-8859-15?Q?F=E4rber?= On Fri, May 10, 2013 at 10:59:22PM +0200, Paolo Bonzini wrote: > Il 10/05/2013 19:41, Anthony Liguori ha scritto: > > Paolo Bonzini writes: > > > >> Il 10/05/2013 16:39, Anthony Liguori ha scritto: > >>> I just oppose the notion of disabling casts and *especially* only > >>> disabling casts for official builds. > >> > >> This actually happens all the time. Exactly this kind of type-safe cast > >> is disabled in releases of GCC, but enabled when building from svn trunk. > > > > Let's assume for a moment that you are right and this behavior is what > > we should have. Let's also assume there is a real regression here > > which has yet to have been established. > > Aurelien timed the effect of my patch two hours before you sent this > message. If it's not a regression in 1.5 (which is quite obvious from > the profile), it is a regression from the introduction of CPU classes > (1.3 or 1.4), when this code didn't exist at all. > > And in 1.5 we introduced virtio-net casts as well (or did mst sneak in > his change anyway? ;)). If 10% is the effect of a few hundred > interrupts/sec, perhaps the same effect is visible on a few thousand > packets/sec. I wouldn't bet against that one week from release. I have run perf top on a KVM x86-64 instance running iperf. I measured around 3% of the CPU taken by g_hash_table_lookup + g_str_hash + __strcmp_sse42. I don't know how it was before though. -- Aurelien Jarno GPG: 1024D/F1BCDB73 aurelien@aurel32.net http://www.aurel32.net