From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:58926) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1eFLoQ-0002jS-Gd for qemu-devel@nongnu.org; Thu, 16 Nov 2017 10:10:46 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1eFLoL-0007Hz-Kf for qemu-devel@nongnu.org; Thu, 16 Nov 2017 10:10:42 -0500 Received: from mx1.redhat.com ([209.132.183.28]:57906) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1eFLoL-0007Es-E5 for qemu-devel@nongnu.org; Thu, 16 Nov 2017 10:10:37 -0500 Date: Thu, 16 Nov 2017 15:10:32 +0000 From: "Richard W.M. Jones" Message-ID: <20171116151031.GV2787@redhat.com> References: <20171115115246.GA1955@redhat.com> <20171116144746.GE29106@stefanha-x1.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20171116144746.GE29106@stefanha-x1.localdomain> Subject: Re: [Qemu-devel] Effect of qemu-img convert -m and -W options List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Stefan Hajnoczi Cc: libguestfs@redhat.com, pl@kamp.de, qemu-devel@nongnu.org On Thu, Nov 16, 2017 at 02:47:46PM +0000, Stefan Hajnoczi wrote: > The threads you observed are the thread pool that performs > preadv(2)/pwritev(2) syscalls. The Linux AIO API could be used instead > and does not use threads for read and write operations. I guess if I used AIO then I wouldn't get any parallelism at all since Linux doesn't block on local file access (at least, it never used to)? > Interesting. Did you perform multiple runs of each setting to verify > that the benchmark results are stable with little volatility? I retested the -m 8 no-W/-W ones because those were so unexpected and those are repeatable. > Which command-line did you use to create the preallocated qcow2 file? What I actually did was qemu-img convert -n into the existing qcow2 file, so there was no separate command for that. > Are the source and target files on the same file system and host block > device? The benefit of using multiple coroutines depends on the > performance characteristics of the source and target files. Both local filesystems, but on different SATA devices. Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com virt-builder quickly builds VMs from scratch http://libguestfs.org/virt-builder.1.html