Re: [ANNOUNCE] kvm-14 release

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

Aurelien Jarno wrote:
> 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.
>   

Real workloads (likr this) are more important than synthetic benchmarks.

> 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
>   

Is this qemu 0.8.2 or qemu 0.9.0?

> 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
>   

So far so good.  Steady improvement.  The low system time indicates a 
lot of I/O and inefficiency in the qemu device emulation (guest time is 
charged as system time).

> 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.
>   

kvm-14 is mostly qemu 0.9.0.  Do you get the same results with kvm-14 
-no-kvm?

What is your disk image file format, or are you using a partition?

Do the results change (on kvm-14) if you pin the guest to a core with 
'taskset 1 qemu ...'



Thank you for taking the time to do real measurements and report the 
results clearly.  That makes it possible (I hope) to find the cause and 
fix it.

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


-------------------------------------------------------------------------
Take Surveys. Earn Cash. Influence the Future of IT
Join SourceForge.net's Techsay panel and you'll get the chance to share your
opinions on IT & business topics through brief surveys-and earn cash
http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV