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

[Avi Kivity <avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org>]

Aurelien Jarno wrote:
> On Sat, Jul 21, 2007 at 12:25:45AM +0200, Aurelien Jarno wrote:
>   
>> Hi,
>>
>> I have just noticed that there is a huge performance regression in
>> network transfers between kvm-29 and kvm-31. Using the RTL8139 emulated
>> card, I have seen the network speed has been divided by 27!!! I haven't
>> made precise speed measurements with other emulated card, but the 
>> network speed has been reduced by the same order.
>>
>> Those tests have been done on a Core 2 CPU.
>>
>> After some tests I have seen that the problem lies in the user part. I
>> will do a git bisect tomorrow to find the patch that has caused the
>> problem, unless somebody already find it.
>>     
>
> 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?

-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.


-------------------------------------------------------------------------
This SF.net email is sponsored by: Microsoft
Defy all challenges. Microsoft(R) Visual Studio 2005.
http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/