Re: [ANNOUNCE] kvm-14 release

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

Avi Kivity a écrit :
> Aurelien Jarno wrote:
>> The bad news is that kvm-14 seems to be a lot slower than kvm-12 +
>> modules from kernel 2.6.20. This is the case with a GNU/kFreeBSD guest.
>> kvm-12 was about 1.5 time faster than qemu + kqemu. kvm-20 is slower
>> than qemu without kqemu...
>>
>> Does anybody have an idea about this performance regression?
>>   
> 
> What is your workload?  How are you measuring performance?

Sorry to answer only now, it took me some time to do some more
measurements and have some numbers. I am simply building a Debian
package (simulpic) and measuring the build time. Basically the command is:

  apt-get source simulpic
  cd simulpic-2005-1-28
 time debuild -uc us

It surely not a performance index, but I guess it is ok to compare
performances between version. It is also quite representative of my use
of the machine.

The guest is Debian GNU/kFreeBSD amd64 (ie FreeBSD kernel + GNU libc).
It is accessed via ssh, and kvm is started with -nographic, so there is
no influence of xorg.

I am doing my tests on an Athlon X2 3800+ machine, running a 2.6.20
kernel. During all my tests, the machine is not loaded with other tasks
(except systems tasks), so qemu or kvm have a full core available. Top
shows that the core is used between 95 and 100% during the whole build
in all cases.

The tests I have made are presented below. In all cases I have verified
that the real time correspond to the time of my wall clock, it is
correct in all case given the resolution of my wall clock (1 s):

qemu
----
real    3m16.626s
user    2m22.654s
sys     0m41.738s

qemu + kqemu
------------
real    0m51.529s
user    0m11.775s
sys     0m36.215s

kvm 12 + modules from kernel 2.6.20
-----------------------------------
real    0m30.635s
user    0m16.357s
sys     0m8.511s

kvm 12
------
real    0m25.357s
user    0m16.259s
sys     0m6.496s

kvm 13
------
real    0m23.415s
user    0m15.177s
sys     0m5.811s

kvm 14
------
real    7m47.310s
user    5m17.359s
sys     2m3.184s


Using kvm 14, the system is clearly not responsive at all. You can see
that without running a benchmark.

Also running Hurd under kvm shows the same problem, though I can't make
such measurements, because it does not run under kvm < 14. Note however
that the ping time of the guest machine running Hurd during I/O
increases from a few milliseconds to a dozen of seconds.

-- 
  .''`.  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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