mirror of
https://github.com/clearlinux/kvmtool.git
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Prasad Joshi
3309045f38
QCOW uses two tables level1 (L1) table and level2 (L2) table. The L1 table
points to offset of L2 table. When a QCOW image is probed, the L1 table is
cached in the memory to avoid reading it from disk on every access. This
caching improves the performance.
The similar performance improvement can be observed when L2 tables are cached.
It is impossible to cache all of the L2 tables because of the memory
constraint. The patch adds L2 table caching capability for up to 32 L2 tables,
it uses combination of RB tree and List to manage the L2 cached tables. The
link list implementation helps in building simple LRU structure and RB tree
helps to search cached table efficiently.
To calculate the performance numbers, the VM was started with following
command line arguments
$ ./kvm run -d /dev/shm/kvm_ubuntu_server.qcow2 --params "root=/dev/vda1" \
> -m 2048
Without Cache
=============
$ fio fio-mixed.job
[...]
fio-sync: (groupid=3, jobs=1): err= 0: pid=563
read : io=102400KB, bw=31239KB/s, iops=429 , runt= 3278msec
clat (usec): min=4 , max=31668 , avg=1663.94, stdev=1810.37
lat (usec): min=281 , max=658022 , avg=162456.88, stdev=242272.58
bw (KB/s) : min=21536, max=29322, per=20.77%, avg=25956.50, stdev=2755.33
write: io=34688KB, bw=13235KB/s, iops=183 , runt= 2621msec
clat (usec): min=77 , max=1619 , avg=431.80, stdev=343.81
lat (usec): min=78 , max=1620 , avg=433.11, stdev=343.83
bw (KB/s) : min=11168, max=14447, per=26.34%, avg=13246.00, stdev=1293.73
[...]
Run status group 0 (all jobs):
READ: io=409600KB, aggrb=74594KB/s, minb=19096KB/s, maxb=20917KB/s,
mint=5013msec, maxt=5491msec
WRITE: io=139552KB, aggrb=42624KB/s, minb=10263KB/s, maxb=14463KB/s,
mint=2414msec, maxt=3274msec
Run status group 1 (all jobs):
READ: io=409600KB, aggrb=146442KB/s, minb=37489KB/s, maxb=48680KB/s,
mint=2154msec, maxt=2797msec
WRITE: io=133296KB, aggrb=59613KB/s, minb=15328KB/s, maxb=16774KB/s,
mint=2041msec, maxt=2236msec
Run status group 2 (all jobs):
READ: io=409600KB, aggrb=7178KB/s, minb=1837KB/s, maxb=1840KB/s,
mint=56961msec, maxt=57057msec
WRITE: io=139136KB, aggrb=2446KB/s, minb=600KB/s, maxb=661KB/s,
mint=56238msec, maxt=56880msec
Run status group 3 (all jobs):
READ: io=409600KB, aggrb=124954KB/s, minb=31988KB/s, maxb=37704KB/s,
mint=2781msec, maxt=3278msec
WRITE: io=137936KB, aggrb=50286KB/s, minb=12447KB/s, maxb=13885KB/s,
mint=2621msec, maxt=2743msec
Disk stats (read/write):
vda: ios=118760/16273, merge=0/107354, ticks=159260/658290, in_queue=817410,
util=94.37%
[...]
With Cache
==========
$ fio fio-mixed.job
[...]
fio-sync: (groupid=3, jobs=1): err= 0: pid=573
read : io=102400KB, bw=76704KB/s, iops=1018 , runt= 1335msec
clat (usec): min=0 , max=66131 , avg=591.46, stdev=2582.59
lat (usec): min=66 , max=123396 , avg=25609.49, stdev=38397.57
bw (KB/s) : min=58208, max=59584, per=34.55%, avg=58896.00, stdev=972.98
write: io=35600KB, bw=29373KB/s, iops=381 , runt= 1212msec
clat (usec): min=11 , max=2661 , avg=169.58, stdev=191.60
lat (usec): min=11 , max=2663 , avg=170.91, stdev=191.78
bw (KB/s) : min=27104, max=37664, per=29.98%, avg=32384.00, stdev=7467.05
[...]
Run status group 0 (all jobs):
READ: io=409600KB, aggrb=140562KB/s, minb=35984KB/s, maxb=44450KB/s,
mint=2359msec, maxt=2914msec
WRITE: io=138816KB, aggrb=124722KB/s, minb=31502KB/s, maxb=40180KB/s,
mint=893msec, maxt=1113msec
Run status group 1 (all jobs):
READ: io=409600KB, aggrb=231151KB/s, minb=59174KB/s, maxb=96111KB/s,
mint=1091msec, maxt=1772msec
WRITE: io=141936KB, aggrb=137268KB/s, minb=32340KB/s, maxb=44496KB/s,
mint=813msec, maxt=1034msec
Run status group 2 (all jobs):
READ: io=409600KB, aggrb=9211KB/s, minb=2358KB/s, maxb=2363KB/s,
mint=44367msec, maxt=44468msec
WRITE: io=129808KB, aggrb=2931KB/s, minb=707KB/s, maxb=797KB/s,
mint=43331msec, maxt=44285msec
Run status group 3 (all jobs):
READ: io=409600KB, aggrb=170453KB/s, minb=43636KB/s, maxb=78545KB/s,
mint=1335msec, maxt=2403msec
WRITE: io=138256KB, aggrb=108012KB/s, minb=27648KB/s, maxb=37931KB/s,
mint=879msec, maxt=1280msec
Disk stats (read/write):
vda: ios=120698/16690, merge=0/114742, ticks=113170/304480, in_queue=417560,
util=93.26%
[...]
Summary
=======
Read bandwidth increased by 1.2 to 1.8 times
Write bandwidth increased by 1.1 to 2.9 times
Read latency decreased by small margin of 0.2
Write latency decreased by 0.4
Signed-off-by: Prasad Joshi <prasadjoshi124@gmail.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>