From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:54805) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1THO0W-0006S7-2T for qemu-devel@nongnu.org; Thu, 27 Sep 2012 20:00:41 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1THO0U-0004CV-WB for qemu-devel@nongnu.org; Thu, 27 Sep 2012 20:00:40 -0400 Received: from mail-pb0-f45.google.com ([209.85.160.45]:38545) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1THO0U-0004BV-QZ for qemu-devel@nongnu.org; Thu, 27 Sep 2012 20:00:38 -0400 Received: by pbbrp2 with SMTP id rp2so4333889pbb.4 for ; Thu, 27 Sep 2012 17:00:37 -0700 (PDT) Message-ID: <5064E8A2.4050108@gmail.com> Date: Fri, 28 Sep 2012 08:00:34 +0800 From: ching MIME-Version: 1.0 References: <506044DE.9060701@gmail.com> <5060524C.2070509@redhat.com> <5060E147.3080306@gmail.com> <5061B2AB.8050509@redhat.com> <50623CBC.8050101@gmail.com> <5062B3F7.704@redhat.com> In-Reply-To: <5062B3F7.704@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 09/26/2012 03:51 PM, Kevin Wolf wrote: > Am 26.09.2012 01:22, schrieb ching: >> On 09/25/2012 09:33 PM, Kevin Wolf wrote: >>> Am 25.09.2012 00:40, schrieb ching: >>>> 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? >>> No, that's why it's silent. :-) >>> >>>> 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 >>> This is odd. The point is that with cache=unsafe it shouldn't even be >>> using Linux AIO in the first place. I can't see why there would be any >>> difference between aio=threads and aio=native with cache=unsafe. >>> >>> Kevin >>> >> is it possible to check the open mode of file and whether it is using aio at runtime? > You can attach strace and look for open/pwritev/iosubmit and friends. I > did that yesterday with qemu-io and didn't see any iosubmit for 'qemu-io > -k -t unsafe'. > > Kevin > The output of strace when using aio=native: open("XXXXXX", O_RDWR|O_CLOEXEC) = 14 However, i can no longer reproduce the problem the VM image is defragged, it is weird. Anyway, thank you very much for your help. ching