From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:34175) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1eASvm-00042v-GR for qemu-devel@nongnu.org; Thu, 02 Nov 2017 23:46:07 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1eASvl-00065n-5v for qemu-devel@nongnu.org; Thu, 02 Nov 2017 23:46:06 -0400 Received: from mail-oi0-x242.google.com ([2607:f8b0:4003:c06::242]:50215) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1eASvk-00065F-VR for qemu-devel@nongnu.org; Thu, 02 Nov 2017 23:46:05 -0400 Received: by mail-oi0-x242.google.com with SMTP id q4so1235541oic.7 for ; Thu, 02 Nov 2017 20:46:04 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: References: <20171101094537.GA2786@work-vm> From: Paul Schlacter Date: Fri, 3 Nov 2017 11:46:03 +0800 Message-ID: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] qemu disk use writeback don't take effect in centos 7.2 1511 List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Dr. David Alan Gilbert" Cc: qemu-devel@nongnu.org latest progress=EF=BC=9A use centos 7.2 https://cloud.centos.org/centos/7/images/ test version: 1511 1601 1604 1606 1608 >>From the above version in turn test, found the previous version 1511 1601 1603 have the problem, The latter two versions 1606 1608 are normal, dont't have the prblem, Normal is cache =3D writeback io significantly higher than none mode why? On Wed, Nov 1, 2017 at 8:03 PM, Paul Schlacter wrote: > Hi David: > yes, with the same qemu, centos 7.2 guest cache is writeback and > none, the disk io almost, writeback feeling no effect. > but 7.1/7.3/7.4 cache is writeback was significantly faster than > none model > > On Wed, Nov 1, 2017 at 8:02 PM, Paul Schlacter > wrote: > >> Hi David: >> yes, with the same qemu, centos 7.2 guest cache is writeback and >> none, the disk io almost, writeback feeling no effect. >> but 7.1/7.3/7.4 cache is writeback was significantly faster than >> none model >> >> On Wed, Nov 1, 2017 at 5:45 PM, Dr. David Alan Gilbert < >> dgilbert@redhat.com> wrote: >> >>> * Paul Schlacter (wlfightup@gmail.com) wrote: >>> > qemu version: 2.9.0 >>> > image: centos 7.2 1511 raw >>> > cache mode: writeback >>> > >>> > >>> > In centos7.2 time, the use of writeback and none, the result of dd >>> disk is >>> > the same io, no change >>> > >>> > But I replaced centos7.1 centos7.3 centos7.4 when writeback was >>> > significantly faster than none >>> > >>> > Would like to ask what is going on, how to solve ? >>> >>> Hi Paul, >>> Can you just clarify your setup please; do you mean that >>> with the same qemu setup but a 7.2 guest rather than a 7.1/7.3 guest >>> the behaviour changes? >>> >>> Dave >>> >>> -- >>> Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK >>> >> >> >