Messages in this thread | | | Date | Fri, 12 Nov 1999 10:32:16 -0800 (PST) | From | Linus Torvalds <> | Subject | Re: [Patch] shm bug introduced with pagecache in 2.3.11 |
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On Fri, 12 Nov 1999, Manfred Spraul wrote: > > > And I don't think the serialization is a performance problem, because > > by the time you start paging we're not talking about high performance > > shared memory anyway, and because it's per-segment it is notgoing to make > > "system" performance any worse. > > What about a 100-gigabyte shm segment (on a 64-bit platform) with a fast > scsi disk system? The semaphore will prevent any tagged commands, and it > will downgrade (performance wise) the scsi system to a slow ide disk.
Nope. The swap-in read-ahead still works - the _only_ thing the semaphore does is serialize different processes accessing the same area, and that's as likely to improve performace as to degrade it (potentially less seeking).
> Btw, I'm sure that for multi-threaded applications, the mmap performance > of Linux will be poor because everything is single-threaded. I'll > write a benchmark and compare it with WinNT/Win95.
I will bet you 5 bucks we'll kick ass.
Linus
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