Messages in this thread | | | Date | Fri, 11 Jan 2002 16:15:15 +0000 (GMT) | From | Matthew Kirkwood <> | Subject | Re: [PATCH][RFC] Lightweight user-level semaphores |
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On Fri, 11 Jan 2002, Manfred Spraul wrote:
> > Actually, the more I look at Linus's original idea, the more > > sense it seems to make (and the more I regret scrapping my > > almost-complete implementation of it for the fd idea :) > > Do you have a plan how to implement the no-contention case entirely in > userspace? > That would make them really fast, not just saving 50 or 100 cycles > through a special syscall and bypassing VFS.
Yep, it was really easy. Following Linus' design[0] it was a really easy hack[1].
I'd like these things to be really easily shareable, and that's harder to do when you need to communicate a mapped area and a file descriptor.
But without an obvious handle, it's hard to collect unreferenced locks.
Rusty's idea is nice (though I think it'd be better with a filesystem than a device, so you can share names rather than file descriptors) but the page per lock seems like rather too much overhead.
Matthew.
[0] http://lwn.net/2001/0419/a/lt-semaphores.php3 [1] Kernel patch: http://hairy.beasts.org/usersem-2.4.17.diff (I have a more complete patch on a machine which isn't up right now.) Userspace bit: http://hairy.beasts.org/ust.tar.gz
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