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

From: OHMURA Kei
Subject: Re: [Qemu-devel] Re: [PATCH v2] qemu-kvm: Speed up of the dirty-bitmap-traveling
Date: Thu, 18 Feb 2010 14:57:47 +0900
User-agent: Thunderbird (Windows/20090812)

"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.

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