From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:33989) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Ygv9x-0006K6-3T for qemu-devel@nongnu.org; Sat, 11 Apr 2015 09:09:17 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Ygv9s-0000zN-Uc for qemu-devel@nongnu.org; Sat, 11 Apr 2015 09:09:17 -0400 Received: from mail-wi0-x234.google.com ([2a00:1450:400c:c05::234]:36654) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Ygv9s-0000w8-NY for qemu-devel@nongnu.org; Sat, 11 Apr 2015 09:09:12 -0400 Received: by wizk4 with SMTP id k4so24541214wiz.1 for ; Sat, 11 Apr 2015 06:09:11 -0700 (PDT) Sender: Paolo Bonzini Message-ID: <55291CF2.4000905@redhat.com> Date: Sat, 11 Apr 2015 15:09:06 +0200 From: Paolo Bonzini MIME-Version: 1.0 References: <552834C1.9070105@gmail.com> In-Reply-To: <552834C1.9070105@gmail.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] Very poor IO performance which looks like some design problem. List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: ein , qemu-devel On 10/04/2015 22:38, ein wrote: > > Qemu creates more than 70 threads and everyone of them tries to write to > disk, which results in: > 1. High I/O time. > 2. Large latency. > 2. Poor sequential read/write speeds. > > When I limited number of cores, I guess I limited number of threads as > well. That's why I got better numbers. > > I've tried to combine AIO native and thread setting with deadline > scheduler. Native AIO was much more worse. > > The final question, is there any way to prevent Qemu for making so large > number of processes when VM does only one sequential R/W operation? Use "aio=native,cache=none". If that's not enough, you'll need to use XFS or a block device; ext4 suffers from spinlock contention on O_DIRECT I/O. Paolo