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

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

Avi Kivity a écrit :
> 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?
> 

With -net tap.

-- 
  .''`.  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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