From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:39544) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1VdcMF-0006Vw-O4 for qemu-devel@nongnu.org; Tue, 05 Nov 2013 03:51:40 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1VdcM7-0003sB-7K for qemu-devel@nongnu.org; Tue, 05 Nov 2013 03:51:31 -0500 Received: from mail-we0-x22a.google.com ([2a00:1450:400c:c03::22a]:34957) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1VdcM6-0003ra-VW for qemu-devel@nongnu.org; Tue, 05 Nov 2013 03:51:23 -0500 Received: by mail-we0-f170.google.com with SMTP id u57so3183814wes.15 for ; Tue, 05 Nov 2013 00:51:22 -0800 (PST) Date: Tue, 5 Nov 2013 09:51:15 +0100 From: Stefan Hajnoczi Message-ID: <20131105085115.GA13336@stefanha-thinkpad.redhat.com> References: <1378106712-29856-1-git-send-email-mreitz@redhat.com> <523B134C.8060902@redhat.com> <20130920103202.GA14159@stefanha-thinkpad.redhat.com> <526BBD8D.7010301@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <526BBD8D.7010301@redhat.com> Subject: Re: [Qemu-devel] [PATCH v5 0/8] Add metadata overlap checks List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Max Reitz Cc: Kevin Wolf , qemu-devel@nongnu.org, Stefan Hajnoczi On Sat, Oct 26, 2013 at 03:03:09PM +0200, Max Reitz wrote: > Am 20.09.2013 12:32, schrieb Stefan Hajnoczi: > > On Thu, Sep 19, 2013 at 05:07:56PM +0200, Max Reitz wrote: > >> As far as I understand, the I/O speed (the duration of an I/O > >> operation) should be pretty much the same for all scenarios, > >> however, the latency is the value in question (since the overlap > >> checks should affect the latency only). > > The other value to look at is the host CPU consumption per I/O. In > > other words, the CPU overhead added by performing the extra checks: > > > > efficiency = avg throughput / avg cpu utilization > > > > Once CPU consumption reaches 100% the workload is CPU-bound and we have > > a bottleneck. > > > > Hopefully the efficiency doesn't change noticably either, then we know > > there is no big impact from the extra checks. > > > > Stefan > > Okay, after fixing the VM state in qcow2, I was now finally able to > actually perform the CPU benchmark. On second thought, it wasn't really > neccessary, since I performed most of the tests in RAM anyway, so the > CPU was already the bottleneck for these tests. > > I ran bonnie++ (bonnie++ -s 4g -n 0 -x 16) from an arch live CD ISO on a > 5 GB qcow2 image formatted as ext4, both residing in /tmp; I prepared > the VM state to the point where I just had to press Enter to perform the > test and shut down the VM. I then performed a snapshot and used this > image as the basis for two tests, one with no overlap checks enabled and > one with all of them enabled. > > The time output for both qemu instances was respectively: > > echo 'sendkey ret' | time $QEMU_DIR/x86_64-softmmu/qemu-system-x86_64 > -cdrom arch.iso -drive file=base.qcow2,overlap-check=none -enable-kvm > -vga std -m 512 -loadvm 0 -monitor stdio > d 294.42s user 117.72s system 98% cpu 6:58.00 total > > echo 'sendkey ret' | time $QEMU_DIR/x86_64-softmmu/qemu-system-x86_64 > -cdrom arch.iso -drive file=base.qcow2,overlap-check=all -enable-kvm > -vga std -m 512 -loadvm 0 -monitor stdio > d 298.87s user 119.55s system 100% cpu 6:56.37 total > > So, as you can see, the CPU time differs only marginally (using all > overlap checks instead of none took 1.52 % more CPU time). Good, looks like the impact isn't very noticable. I wonder if that 1.52% is reproducible or just noise, did you run the benchmark multiple times? Stefan