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List:       linux-kernel
Subject:    Re: [Patch] shm bug introduced with pagecache in 2.3.11
From:       Manfred <manfreds () colorfullife ! com>
Date:       1999-11-19 11:30:43
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Linus wrote:
> 
> Re-do this without the ridiculous filesystem, and I'll bother to even
> check the numbers.
> 
The filesystem doesn't affect the numbers: it's a read-only benchmark
with datatransfer rates < 300kB/sec, but Alan asked for an ext2 benchmark
with a faster drive.
I did a second test with ext2/ntfs, 1.9GB file, SCSI-2-narrow drive
(Seagate, 4.5GB)).
I posted the results in this thread, IIRC

* Linux with forked processes is around 30%slower than NT. I don't
know why, I didn't investigate that.
* Linux with processes and NT get faster as I add additional processes.
* with 64 processes, the IO performance has increased by around 50%
compared to the single process case.(both NT and Linux-fork)
* Linux with multiple threads cannot reorder the read operations, and
 1 thread is as fast as 64 threads, ie. we loose around 50% possible
performance due to the mmap semaphore.

> That said, I don't think this can/will be fixed for a 2.4 timeframe,
I didn't expect that. It's something for 2.5

> especially as I haven't heard of any real-life usage where it would be an
> issue..
IMHO that's obvious: "normal" programs are single-threaded or use fork, and
they use read/write for io.
--> the problem only affects multi-threaded, mmap based programs, and they
 are rare. (perhaps Apache 2?)

--
	Manfred

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