Messages in this thread | | | Date | Fri, 19 Nov 1999 13:01:52 +0100 (MET) | From | Richard Guenther <> | Subject | Re: [Patch] shm bug introduced with pagecache in 2.3.11 |
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On Fri, 19 Nov 1999, Manfred wrote:
> Linus wrote: > > * 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.
Uh, thats bad! (see below)
> > 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?)
We are implementing a real-time audio-processing tool which will support tree-like filter-chains, each filter beeing a thread and mmaping parts of a global swap-file (the filters passing data (as pointers to a mmapped area) via sockets).
So is there any way to fix this for 2.4? I dont see how we can use processes and not loose performace at other places.
Btw, I saw patches floating around which add madvise() - will they be included before 2.4? They would be really useful.
Richard.
-- Richard Guenther <richard.guenther@student.uni-tuebingen.de> PGP: 2E829319 - 2F 83 FC 93 E9 E4 19 E2 93 7A 32 42 45 37 23 57 WWW: http://www.anatom.uni-tuebingen.de/~richi/
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