Re: [Xen-devel] 4.2.1: Poor write performance for DomU.

[Steven Haigh <netwiz@xxxxxxxxx>]

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 <netwiz@xxxxxxxxx> 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.

--
Steven Haigh

Email: netwiz@xxxxxxxxx
Web: http://www.crc.id.au
Phone: (03) 9001 6090 - 0412 935 897
Fax: (03) 8338 0299

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