Re: why do I get bad disk write performance in the kernel 3.1?

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Wed, Nov 09, 2011 at 02:52:59PM -0200, Roberto Scudeller wrote:
> Konrad,
> 
> Thanks for help.

OK, so looks like you are using qdisk. Can you try creating an
LVM and blasting the image onto that?

And obviously then using 'phy:/dev/vg_guest/...' ?

You could also try the 'file:/local-disk' which will setup a loopback device
and use that. Try that as well.

> 
> My windows.cfg is:
> name='benchCM-windows-2003-64b-std-test'
> kernel='/usr/lib/xen/boot/hvmloader'
> builder='hvm'
> memory=512
> vcpus=2
> pae=1
> acpi=1
> apic=1
> disk=[ 'tap2:aio:/local-disk/benchCM-windows-2003-64b-std/xvda,xvda,w' ]
> device_model='/usr/lib/xen/bin/qemu-dm'
> boot='c'
> sdl=0
> vnc=1
> vncunused=1
> vnclisten='0.0.0.0'
> vncpasswd=''
> stdvga=0
> extra=''
> on_reboot='restart'
> on_shutdown='destroy'
> ramdisk=''
> image_name=''
> on_crash='destroy'
> bootloader=''
> root=''
> platform='xen'
> network_mode='tap'
> usb = 1
> usbdevice = 'tablet'
> 
> The xvda disk is a raw disk, created with dd.
> I use the windows.cfg in both kernel.
> 
> 
> 
> 2011/11/9 Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
> 
> > On Wed, Nov 09, 2011 at 12:58:27PM -0200, Roberto Scudeller wrote:
> > > Hi all,
> > >
> > > I'm testing the new kernel 3.1 from kernel.org, and xen 4.1.2-rc1-pre.
> > > I execute a CrystalMark IO Benchmark, in windows 2003 VM with gplpv
> > > drivers, and receive an amazing result for reading, but the write numbers
> > > are very disappointing.
> > >
> > > I run the VM in local disk, and receive these numbers:
> > > Seq read: 244 MB/s
> > > 512K read: 239 MB/s
> > > 4K read: 27 MB/s
> > > 4K QD 32: 90 MB/s
> > >
> > > Seq write: 20 MB/s
> > > 512K: 20 MB/s
> > > 4K: 8 MB/s
> > > 4K QD 32: 12MB/s
> > >
> > > In older kernel, 2.6.32.x:
> > > Seq read: 189 MB/s
> > > 512K read: 169 MB/s
> > > 4K read: 11 MB/s
> > > 4K QD 32: 34 MB/s
> > >
> > > Seq write: 177 MB/s
> > > 512K: 166 MB/s
> > > 4K: 12 MB/s
> > > 4K QD 32: 36 MB/s
> > >
> > > Could anyone help me. Why is the new kernel faster in reading, but too
> > slow
> > > writing ?
> >
> > It would help if you gave an idea of what the guest configuration is and
> > what is the backend. It might be that the backend you are using in 3.1 is
> > QEMU qdisk, not xen-blkback.
> >
> 
> 
> 
> -- 
> Roberto Scudeller