Re: Network performance regression between kvm-29 and kvm-31

[Aurelien Jarno <aurelien-rXXEIb44qovR7s880joybQ@public.gmane.org>]

On Sun, Jul 22, 2007 at 01:30:14PM +0300, Avi Kivity wrote:
> Aurelien Jarno wrote:
> >>>
> >>> I finally didn't resist to run git bisect before going to bed...
> >>>
> >>> The patch that causes the regression is:
> >>>
> >>> commit 7d2e674835492040c9baddf0989a95abea9a8d0f
> >>> Author: Avi Kivity <avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org>
> >>> Date:   Sun Jul 15 15:08:23 2007 +0300
> >>>
> >>>     kvm: qemu: synchronous signal handling
> >>>     
> >>>     in order to ensure that signals are handled with the global lock held, we
> >>>     block them, and dequeue them with sigtimedwait().  we can then call the
> >>>     handlers directly.
> >>>     
> >>>     this ensures that the device model and internal qemu data structures are not
> >>>     corrupted by cpu 0 thread handling a signal while cpu 1 is servicing a pio
> >>>     or mmio request.
> >>>
> >>>   
> >>>       
> >> Is this with -net user or -net tap?
> >>
> >>     
> >
> > With -net tap.
> >
> >   
> 
> I pushed a commit which fixes a latency issue with that commit.  However 
> with my test (ping -f against the host) I only get a x2 performance 
> increase.  Can you test kvm-userspace.git?  And can you detail your 
> benchmark?

Yes, that fixes the problem. However it seems it has broken SMP
support, I am not able to boot a linux guest with 2 CPU with this 
patch.

About my benchmark, I am just copying a big file using scp between the
guest and the host, and I saw a drop from 7,5 MiB/s to 280 kiB/s.

Aurelien

-- 
  .''`.  Aurelien Jarno	            | GPG: 1024D/F1BCDB73
 : :' :  Debian developer           | Electrical Engineer
 `. `'   aurel32-8fiUuRrzOP0dnm+yROfE0A@public.gmane.org         | aurelien-rXXEIb44qovR7s880joybQ@public.gmane.org
   `-    people.debian.org/~aurel32 | www.aurel32.net

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