Re: poor OSD performance using kernel 3.4

[Stefan Priebe - Profihost AG <s.priebe@profihost.ag>]

Some speed tests with different Kernel Versions. The same applies to
other FS like btrfs.
I used "rados -p data bench 100 write -t 16" for all tests and a freshly
created FS. mount options were always: noatime,nodiratime,nobarrier.

3.0.30 with XFS

speed is always between 120 and 160MB/s

Total time run:        100.510061
Total writes made:     3605
Write size:            4194304
Bandwidth (MB/sec):    143.468

Average Latency:       0.445714
Max latency:           1.99929
Min latency:           0.084812

3.2.18 with XFS

speed is between 40 and 170MB/s

Total time run:        100.795653
Total writes made:     3384
Write size:            4194304
Bandwidth (MB/sec):    134.292

Average Latency:       0.476297
Max latency:           2.92075
Min latency:           0.084884

3.3.7 with XFS

!! speed heavily jumps between 0 and 170 MB/s !!

Total time run:        107.398166
Total writes made:     2455
Write size:            4194304
Bandwidth (MB/sec):    91.435

Average Latency:       0.699819
Max latency:           13.8117
Min latency:           0.084624

3.4 with XFS

!! speed heavily jumps between 0 and 130 MB/s - most if the time it's
near 0 !!

Total time run:        115.433531
Total writes made:     468
Write size:            4194304
Bandwidth (MB/sec):    16.217

Average Latency:       3.9452
Max latency:           53.4356
Min latency:           0.091276


Stefan