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

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

> Sounds logical - do you have numbers on the improvement?

Sure.  The patch showed approximately 3-7 times speed up when measured with 
rdtsc.  The test environment and detailed results are described below.

---
tmp = rdtsc();
/* function of original code*/
t1 += rdtsc() - tmp;
    
tmp = rdtsc();
/* function of this patch */
t2 += rdtsc() - tmp;
---

Test Envirionment:
CPU: 4x Intel Xeon Quad Core 2.66GHz
Mem size: 6GB
kvm version: 2.6.31-17-server
qemu version: commit ed880109f74f0a4dd5b7ec09e6a2d9ba4903d9a5

Host OS: Ubuntu 9.10 (kernel 2.6.31)
Guest OS: Debian/GNU Linux lenny (kernel 2.6.26)
Guest Mem size: 512MB

We executed live migration three times.  This data shows, how many times the 
function is called (#called), runtime of original (orig.), runtime of this 
patch (patch), speedup ratio (ratio), when live migration run.

Experimental results:
Test1: Guest OS read 3GB file, which is bigger than memory.
#called     orig.(msec)     patch(msec)     ratio
114         1.00            0.15            6.76
132         1.57            0.25            6.26
96          1.00            0.16            6.27
 
Test2: Guest OS read/write 3GB file, which is bigger than memory.
#called     orig.(msec)     patch(msec)     ratio
2196        38.1            10.6            3.59
2256        39.6            10.8            3.68
2112        36.3            10.3            3.53



> Would be great if you could provide a version for upstream as well
> because it will likely replace this qemu-kvm code on day.

O.K.  We'll prepare it.

We'll also post a patch set to quicken dirty pages checking in ram_save_block
and ram_save_live soon.