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SubjectRe: [Patch] shm bug introduced with pagecache in 2.3.11
Dominik Kubla wrote:
> Gerard was referring to the source code of the _OS_, not your benchmark!
> And i have to agree with him: There is no way to understand what a OS
> is really doing without looking at the source.

In this case you don't need the source code:
Do you have a really noisy drive with a slow seek time?
Then you would hear the difference:
- WinNT and Linux-fork sound 'round' with lots of threads/processes, and
the performance increases.

- Linux-multithread always sounds identical (1 thread or 64); the
performance doesn't change.

You don't need to be a rocket scientist to figure out that the cause is
the mmap semaphore, ie that Linux single threads the io for
multi-threaded applications.
Linux with multiple processes or WinNT reorder the disk io, and thus
they get faster with more processes/threads.

--
Manfred
P.S.: if you prefer to look at the source, then compare Linux-fork and
Linux-multithread.


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