From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Dr. David Alan Gilbert" Subject: Re: [Qemu-devel] virtio-console downgrade the virtio-pci-blk performance Date: Mon, 1 Oct 2018 12:41:47 +0100 Message-ID: <20181001114146.GA2508@work-vm> References: Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org To: Feng Li Cc: linux-kernel , qemu-discuss@nongnu.org, qemu-devel@nongnu.org, "linux-scsi@vger.kernel.org" List-Id: linux-scsi@vger.kernel.org * Feng Li (lifeng1519@gmail.com) wrote: > Hi, > I found an obvious performance downgrade when virtio-console combined > with virtio-pci-blk. > > This phenomenon exists in nearly all Qemu versions and all Linux > (CentOS7, Fedora 28, Ubuntu 18.04) distros. > > This is a disk cmd: > -drive file=iscsi://127.0.0.1:3260/iqn.2016-02.com.test:system:fl-iscsi/1,format=raw,if=none,id=drive-virtio-disk0,cache=none,aio=native > -device virtio-blk-pci,scsi=off,bus=pci.0,addr=0x6,drive=drive-virtio-disk0,id=virtio-disk0,bootindex=1,write-cache=on > > If I add "-device > virtio-serial-pci,id=virtio-serial0,bus=pci.0,addr=0x5 ", the virtio > disk 4k iops (randread/randwrite) would downgrade from 60k to 40k. > > In VM, if I rmmod virtio-console, the performance will back to normal. > > Any idea about this issue? > > I don't know this is a qemu issue or kernel issue. It sounds odd; can you provide more details on: a) The benchmark you're using. b) the host and the guest config (number of cpus etc) c) Why are you running it with iscsi back to the same host - why not just simplify the test back to a simple file? Dave > > Thanks in advance. > -- > Thanks and Best Regards, > Alex > -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK