Re: [Qemu-devel] Re: [PATCH v2] qemu-kvm: Speed up of the dirty-bitmap-traveling

[OHMURA Kei <ohmura.kei@lab.ntt.co.jp>]

>>>>> "We think"? I mean - yes, I think so too. But have you actually measured it?
>>>>> How much improvement are we talking here?
>>>>> Is it still faster when a bswap is involved?
>>>> Thanks for pointing out.
>>>> I will post the data for x86 later.
>>>> However, I don't have a test environment to check the impact of bswap.
>>>> Would you please measure the run time between the following section if possible?
>>> It'd make more sense to have a real stand alone test program, no?
>>> I can try to write one today, but I have some really nasty important bugs to fix first.
>>
>> OK.  I will prepare a test code with sample data.  Since I found a ppc machine around, I will run the code and post the results of
>> x86 and ppc.
>>
>>
>> By the way, the following data is a result of x86 measured in QEMU/KVM.  
>> This data shows, how many times the function is called (#called), runtime of original function(orig.), runtime of this patch(patch), speedup ratio (ratio).
> 
> That does indeed look promising!
> 
> Thanks for doing this micro-benchmark. I just want to be 100% sure that it doesn't affect performance for big endian badly.


I measured runtime of the test code with sample data.  My test environment 
and results are described below.

x86 Test Environment:
CPU: 4x Intel Xeon Quad Core 2.66GHz
Mem size: 6GB

ppc Test Environment:
CPU: 2x Dual Core PPC970MP
Mem size: 2GB

The sample data of dirty bitmap was produced by QEMU/KVM while the guest OS
was live migrating.  To measure the runtime I copied cpu_get_real_ticks() of
QEMU to my test program.


Experimental results:
Test1: Guest OS read 3GB file, which is bigger than memory. 
       orig.(msec)    patch(msec)    ratio
x86    0.3            0.1            6.4 
ppc    7.9            2.7            3.0 

Test2: Guest OS read/write 3GB file, which is bigger than memory. 
       orig.(msec)    patch(msec)    ratio
x86    12.0           3.2            3.7 
ppc    251.1          123            2.0 


I also measured the runtime of bswap itself on ppc, and I found it was only 
just 0.3% ~ 0.7 % of the runtime described above.