Hi All,
I am kind of new to UML and I am experiencing a very strange performance hinder with it.
I am running two benchmarks; one that writes a 50Mbyte file and the other one reads a 50Mbyte file.
I tried the benchmarks with and without setting the O_DIRECT flag, in which cases the whole task is done in a matter of seconds(10-30 seconds) except when reading the file with O_DIRECT flag on. In this case, it takes 18-20 min!!!
I am running UML 2.4.19 on top of kernel 2.4.25. I have time output like that (average of 20 runs)
Operation
|
User Time (sec)
|
Sys Time(sec)
|
Wall Clock Time(sec)
|
Write Without O_DIRECT
|
5.612000
|
0.117500
|
27.164500
|
Write With O_DIRECT
|
10.007000
|
0.017000
|
22.199500
|
Read without O_DIRECT
|
3.035000
|
0.091000
|
7.760000
|
Read With O_DIRECT
|
21.492000
|
29.680000
|
1133.054000
|
I would appreciate it very much if somebody would explain to me how to solve that strange performance problem, or even explain why does it happen for reading with O_DIRECT but not without !!??
Thanks allot,
Lamia Youseff
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