Re: Synchronization primitives in UML (was: Re: [uml-devel] Re: [patch 09/20] uml: use SIG_IGN for empty sighandler)

From: Jeff Dike
Date: Tue Nov 09 2004 - 13:41:47 EST

blaisorblade_spam@xxxxxxxx said:
> I also understand now what all this is for. When I have time for this,
> I'll at least copy and paste your mail into a comment, with any
> needed adjustment.

That would be a good idea.

> For the semaphore issue, I have some ideas (like using futexes) which
> need to be developed a bit:

> 1) I want to create a semaphore API in os_*.
> 2) It will be able to use socketpairs.
> 3) It will be able to use futexes, if they are
> non-persistant and usable without too much issues (the same way we
> are going to support Async I/O).
> 4) It will be used first by the code
> which could really benefit from the performance increase.
> 5) It won't
> use persistant objects.

This all sounds good, although there are simplicity benefits to just using
one underlying mechanism, as long as there are no overriding disadvantages
to it.

> Any comment on these issues? Also, apart TT context switching, is
> there any other performance-sensitive use of semaphores, which would
> benefit from using futexes?

Offhand, I think context switching is the most sensitive one.

> Yes, semget and friends are uglier.
> But don't think that the current nested code is simple to read - three
> semaphores at a time, without a clear name, are not the clearer code
> on the world.

What nested code are you talking about?


To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at