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Subject[Bench] Slow tiotest read in Kernel 2.2.16+
Ive been seeing poor read results from tiotest in recent 2.2 kernels
since 2.2.16.
The performance is fine with 1 thread but slows right down with 8.
I include the tiotest results here but I see similar results with iozone
-t.


Kernel 2.2.15

[robert@testmac25 robert]$ tiotest -f 30 -t 8 -r 0
Tiotest results for 8 concurrent io threads:

,----------------------------------------------------------------------.
| Item | Time | Rate | Usr CPU | Sys CPU |
+-----------------------+----------+--------------+----------+---------+
| Write 240 MBs | 20.8 s | 11.533 MB/s | 0.3 % | 14.0 % |
| Read 240 MBs | 19.2 s | 12.531 MB/s | 0.3 % | 8.9 % |
`----------------------------------------------------------------------'


Kernel 2.2.16

[robert@testmac25 robert]$ tiotest -f 30 -t 8 -r 0
Tiotest results for 8 concurrent io threads:

,----------------------------------------------------------------------.
| Item | Time | Rate | Usr CPU | Sys CPU |
+-----------------------+----------+--------------+----------+---------+
| Write 240 MBs | 23.9 s | 10.058 MB/s | 0.0 % | 12.8 % |
| Read 240 MBs | 105.4 s | 2.276 MB/s | 0.1 % | 2.5 % |
`----------------------------------------------------------------------'


Kernel 2.2.18pre15

[robert@testmac25 robert]$ tiotest -f 30 -t 8 -r 0
Tiotest results for 8 concurrent io threads:

,----------------------------------------------------------------------.
| Item | Time | Rate | Usr CPU | Sys CPU |
+-----------------------+----------+--------------+----------+---------+
| Write 240 MBs | 22.5 s | 10.688 MB/s | 0.3 % | 12.5 % |
| Read 240 MBs | 98.0 s | 2.450 MB/s | 0.1 % | 2.7 % |
`----------------------------------------------------------------------'


Robert Cohen
TLTSU Unix Support
Australian National University
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