From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [User question] Huge buffer size on KVM host Date: Thu, 16 Aug 2012 17:57:39 +0300 Message-ID: <502D0A63.1070608@redhat.com> References: <502B5877.1080901@digitalmedics.de> <502B883D.5080402@redhat.com> <4061CC51-5F7E-4C94-AC5E-EE857BCA412C@digitalmedics.de> <502B9CAC.3020705@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: kvm@vger.kernel.org, "libvir-list@redhat.com" To: Martin Wawro Return-path: Received: from mx1.redhat.com ([209.132.183.28]:14885 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932696Ab2HPO5u (ORCPT ); Thu, 16 Aug 2012 10:57:50 -0400 In-Reply-To: Sender: kvm-owner@vger.kernel.org List-ID: On 08/16/2012 05:54 PM, Martin Wawro wrote: > > On Aug 15, 2012, at 2:57 PM, Avi Kivity wrote: > >>> >>> We are using logical volumes and the cache is set to 'none'. >> >> Strange, that should work without any buffering. >> >> What the contents of >> >> /sys/block/sda/queue/hw_sector_size >> >> and >> >> /sys/block/sda/queue/logical_block_size >> >> ? >> > > Hi Avi, > > It seems that the kernel on that particular machine is too old, those entries are > not featured. We checked on a comparable setup with a newer kernel and both entries > were set to 512. > > We also did have a third more thorough look on the caching. It turns out that the > virt-manager does not seem to honor the caching adjusted in the GUI correctly. > We disabled caching on all virtual devices for this particular VM and checking > with "ps -fxal" revealed, that only one of those devices (and a rather small one too) > had this set. We corrected this in the XML file directly and the buffer size > currently resides at around 1.8 GB after rebooting the VM (the only virtio device > not having the cache=none option set is now the (non-mounted) cdrom). > cc += libvirt-list Is there a reason that cdroms don't get cache=none? -- error compiling committee.c: too many arguments to function