On Fri, 8 Mar 2002, Hubertus Franke wrote:
>
> Could you also comment on the functionality that has been discussed.
First off, I have to say that I really like the current patch by Rusty.
The hashing approach is very clean, and it all seems quite good. As to
specific points:
> (I) the fairness issues that have been raised.
> do you support two wakeup mechanism: FUTEX_UP and FUTEX_UP_FAIR
> or you don't care about fairness and starvation
I don't think fairness and starvation is that big of a deal for
semaphores, usually being unfair in these things tends to just improve
performance through better cache locality with no real downside. That
said, I think the option should be open (which it does seem to be).
For rwlocks, my personal preference is the fifo-fair-preference (unlike
semaphore fairness, I have actually seen loads where read- vs
write-preference really is unacceptable). This might be a point where we
give users the choice.
I do think we should make the lock bigger - I worry that atomic_t simply
won't be enough for things like fair rwlocks, which might want a
"cmpxchg8b" on x86.
So I would suggest making the size (and thus alignment check) of locks at
least 8 bytes (and preferably 16). That makes it slightly harder to put
locks on the stack, but gcc does support stack alignment, even if the code
sucks right now.
Linus
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This archive was generated by hypermail 2b29 : Fri Mar 15 2002 - 22:00:09 EST