From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:38274) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1YhTRi-0002tS-Aj for qemu-devel@nongnu.org; Sun, 12 Apr 2015 21:45:55 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1YhTRf-0004R6-4j for qemu-devel@nongnu.org; Sun, 12 Apr 2015 21:45:54 -0400 Received: from mx1.redhat.com ([209.132.183.28]:49721) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1YhTRe-0004Qw-Va for qemu-devel@nongnu.org; Sun, 12 Apr 2015 21:45:51 -0400 Date: Mon, 13 Apr 2015 09:45:46 +0800 From: Fam Zheng Message-ID: <20150413014546.GB14218@ad.nay.redhat.com> References: <552834C1.9070105@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <552834C1.9070105@gmail.com> 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 Cc: qemu-devel@nongnu.org On Fri, 04/10 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? aio=native will make QEMU only submit IO from the IO thread, so you shouldn't see 70 threads with that. And that should usually be a better option for performance. Fam