From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:38533) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1UasPW-0005fq-Ho for qemu-devel@nongnu.org; Fri, 10 May 2013 14:51:23 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1UasPR-0000G2-Fi for qemu-devel@nongnu.org; Fri, 10 May 2013 14:51:18 -0400 Received: from e23smtp01.au.ibm.com ([202.81.31.143]:49777) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1UasPQ-0000FA-T7 for qemu-devel@nongnu.org; Fri, 10 May 2013 14:51:13 -0400 Received: from /spool/local by e23smtp01.au.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Sat, 11 May 2013 04:43:29 +1000 Received: from d23relay05.au.ibm.com (d23relay05.au.ibm.com [9.190.235.152]) by d23dlp01.au.ibm.com (Postfix) with ESMTP id 218302CE804A for ; Sat, 11 May 2013 04:51:07 +1000 (EST) Received: from d23av03.au.ibm.com (d23av03.au.ibm.com [9.190.234.97]) by d23relay05.au.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id r4AIb3fp22937758 for ; Sat, 11 May 2013 04:37:03 +1000 Received: from d23av03.au.ibm.com (loopback [127.0.0.1]) by d23av03.au.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id r4AIp6UW010033 for ; Sat, 11 May 2013 04:51:06 +1000 From: Anthony Liguori In-Reply-To: <20130510155632.GL31148@hall.aurel32.net> References: <1368188203-3407-1-git-send-email-pbonzini@redhat.com> <20130510155632.GL31148@hall.aurel32.net> Date: Fri, 10 May 2013 13:50:37 -0500 Message-ID: <87ppwyis8y.fsf@codemonkey.ws> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii 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: Aurelien Jarno , Paolo Bonzini Cc: mst@redhat.com, qemu-devel@nongnu.org, Andreas Faerber Aurelien Jarno writes: > On Fri, May 10, 2013 at 02:16:34PM +0200, Paolo Bonzini wrote: >> Cast debugging can have a substantial cost (20% or more, measured by >> Aurelien on qemu-system-ppc64). Instead of adding special-cased "fast >> casts" in the hot paths, we can just disable it in releases. At the >> same time, add tracing facilities that simplify the analysys of those >> problems that cast debugging would reveal. >> >> At least patches 1-7 are for 1.5. >> >> Paolo Bonzini (9): >> qom: improve documentation of cast functions >> qom: allow casting of a NULL class >> qom: add a fast path to object_class_dynamic_cast >> qom: pass file/line/function to asserting casts >> qom: trace asserting casts >> qom: allow turning cast debugging off >> build: disable QOM cast debugging for official releases >> qom: simplify object_class_dynamic_cast, part 1 >> qom: simplify object_class_dynamic_cast, part 2 >> >> configure | 20 ++++++++------ >> include/qom/object.h | 40 ++++++++++++++++++++++----- >> qom/object.c | 77 ++++++++++++++++++++++++++++++++++------------------ >> trace-events | 3 ++ >> 4 files changed, 99 insertions(+), 41 deletions(-) >> > > I have tested this series with qemu-system-ppc64, on a Core i7 2600 CPU. > The process was set to a single core using taskset. Inside the guest > (Debian ppc64 from debian-ports), I ran the command three times: > > lintian g++-4.8_4.8.0-6_ppc64.deb > > I used lintian as it's a perl code, that trigger the discussion about > sparc/ppc comparison. > > First of all with this patch series, the object_class_dynamic_cast calls > went down to below 0.1% when using perf top. Before the patch series was > applied, the command took in average on 3 runs 142.4s. With the patch > series, it went down to 129.8s, so almost 9% faster. I just posted another patch which I believe will also reduce this overhead without eliminating the checks. We do a staggering number of casts... The patch I posted makes the overwhelming majority of them nothing more than a single pointer comparison and a couple derefs. Regards, Anthony Liguori > > To improve the performance a bit more, and come back to the same kind of > code as before, we should move simple accessors from qom/*.c to > include/qom/*.h and mark them as inline, so that they can be removed by > the compiler. Currently, even if the function is simple it's still a > call/ret in the hot path instead of a simple pointer addition. > > -- > Aurelien Jarno GPG: 1024D/F1BCDB73 > aurelien@aurel32.net http://www.aurel32.net