Re: [Xen-devel] why do I get bad disk write performance in the kernel 3.1?

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Thu, 2011-11-10 at 03:42 +0000, Konrad Rzeszutek Wilk wrote:

> 
> 
> OK, so looks like you are using qdisk. [...]

That depends on whether Roberto is using xm/xend or xl, I think.
Roberto?

I'm not sure what xend does for 'tap2:aio' if blktap isn't available. I
suspect it doesn't fallback to qdisk. Roberto can you report the content
of xenstore under /local/domain/0/backend/ (use xenstore-ls <path>).

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

This is true with xm/xend but with xl you will need to manually setup
the looback and use phy:/dev/loop in order to perform this experiment.
For xl file: turns into qdisk unless blktap is available.

Ian.

> 
> > 
> > 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@xxxxxxxxxx>
> > 
> > > 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
> 
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