From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Cooper Subject: Re: 4.2.1: Poor write performance for DomU. Date: Wed, 20 Feb 2013 12:48:03 +0000 Message-ID: <5124C603.6000902@citrix.com> References: <51243089.8020307@crc.id.au> <512488AC.1020702@citrix.com> <51248E23.7060408@crc.id.au> <51249C11.3050800@crc.id.au> <5124AF9F02000078000BFA35@nat28.tlf.novell.com> <5124AE19.2000802@citrix.com> <5124AECA.4060503@crc.id.au> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <5124AECA.4060503@crc.id.au> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Steven Haigh Cc: Roger Pau Monne , Jan Beulich , "xen-devel@lists.xen.org" List-Id: xen-devel@lists.xenproject.org On 20/02/13 11:08, Steven Haigh wrote: > On 20/02/2013 10:06 PM, Andrew Cooper wrote: >> On 20/02/13 10:12, Jan Beulich wrote: >>>>>> On 20.02.13 at 10:49, Steven Haigh wrote: >>>> My build of Xen 4.2.1 also has all of the recent security advisories >>>> patched as well. Although it is interesting to note that >>>> downgrading to >>>> Xen 4.1.2 made no difference to write speeds. >>> Not surprising at all, considering that the hypervisor is only a >>> passive >>> library for all PV I/O purposes. You're likely hunting for a kernel >>> side >>> regression (and hence the mentioning of the hypervisor version as >>> the main factor in the subject is probably misleading). >>> >>> Jan >> >> Further to this, do try to verify if your disk driver has changed >> recently to use >0 order page allocations for DMA. If it has, then >> speed will be much slower as there will now be the swiotlb cpu-copy >> overhead. > > Any hints on how to do this? ;) > > The kernel modules in use for my SATA drives are ahci and sata_mv. > There are 6 drives in total on the system. > > sda + sdb = RAID1 > sd[c-f] = RAID6 > > sda, sdb, sdc and sdd are on the onboard SATA controller (ahci) > sde, sdf are on the sata_mv 4x PCIe controller. > Sadly that is a hard question to answer, and is driver specific. I cant suggest an easy way other than digging into the source. ~Andrew