From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:50207) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1TGHK1-0002Yy-ND for qemu-devel@nongnu.org; Mon, 24 Sep 2012 18:40:15 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1TGHK0-0005e2-2E for qemu-devel@nongnu.org; Mon, 24 Sep 2012 18:40:13 -0400 Received: from mail-pb0-f45.google.com ([209.85.160.45]:37525) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1TGHJz-0005cr-QB for qemu-devel@nongnu.org; Mon, 24 Sep 2012 18:40:12 -0400 Received: by pbbrp2 with SMTP id rp2so2072604pbb.4 for ; Mon, 24 Sep 2012 15:40:10 -0700 (PDT) Message-ID: <5060E147.3080306@gmail.com> Date: Tue, 25 Sep 2012 06:40:07 +0800 From: ching MIME-Version: 1.0 References: <506044DE.9060701@gmail.com> <5060524C.2070509@redhat.com> In-Reply-To: <5060524C.2070509@redhat.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] linux aio and cache mode List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Kevin Wolf Cc: qemu-devel@nongnu.org On 09/24/2012 08:30 PM, Kevin Wolf wrote: > Am 24.09.2012 13:32, schrieb ching: >> Hi all, >> >> My host is qemu-1.1.1 and x64 kernel 3.5.4. The guest is using aio="native" >> >> I am trying to use unsafe cache mode to boost i/o performance. > aio=native requires the image to be opened with O_DIRECT, i.e. > cache=none or cache=directsync. If you specify a different cache option, > it will silently fall back to aio=threads. > > Kevin > will qemu log a entry for the silent fallback? Reason: I am testing sparse image on btrfs with mount option: rw,noatime,space_cache,autodefrag,inode_cache i encounter a speed difference (around 2X-3X) between aio=threads,cache=unsafe and aio=native,cache=unsafe aio=threads is much faster, i guest there is conflict between "autodefrag" and linux aio ching