[Qemu-devel] Re: [PATCH 10/12] kvm: enable smp > 1

[Udo Lembke]

Avi Kivity schrieb:
> On 05/19/2010 12:57 PM, Udo Lembke wrote:
> > Jan Kiszka schrieb:
> > > ...
> > > --enable-io-thread?
> > >
> > > If you had it disabled, it would also answer my question if -smp works
> > > without problems without that feature.
> > >
> > > Jan
> > Hi,
> > i have a dumb question: what is the "--enable-io-thread"? Is this a 
> > kvm-switch?
>
> It's a ./configure switch for upstream qemu (don't use with qemu-kvm 
> yet).
>
> > My kvm 0.12.4 don't accept this switch. I'm know only "threads=n" as 
> > smp-parameter and "aio=threads" as drive-parameter.
> >
> > Because i look for a solution for a better io-performance of 
> > windows-guest with more than one cpu...
>
> Unrelated, what are your smp issues?
If i use one cpu i got a good io-performance:
e.g. over 500MB/s at the profile "install" of the io-benchmark h2benchw.exe.
( aio=threads | SAS-Raid-0 | ftp://ftp.heise.de/pub/ct/ctsi/h2benchw.zip 
| hwbenchw.exe -p -w iotest 0)
The same test but with two cpus gives results between 27 and 298 MB/s!

Also in real life it's noticeable not only with an benchmark. I use a 
win-vm with two cpu for postscript-ripping and have a performance drop 
due to the bad io.

Udo