Forgive my naivete, but do futex's implement some priority algorithm for
which process gets control. One of the problems as I understand it is
that linux does (did ) not implement a priority algorithm, so it is
possible for the context which just gave up control to be the next
context woken up, which of course is a complete waste of time.
--dc--
Tom Lane wrote:
Manfred Spraul <[EMAIL PROTECTED]> writes:
Tom Lane wrote:
The bigger problem here is that the SMP locking bottlenecks we are
currently seeing are *hardware* issues (AFAICT anyway). The only way
that futexes can offer a performance win is if they have a smarter way
of executing the basic atomic-test-and-set sequence than we do;
lwlocks operations are not a basic atomic-test-and-set sequence. They
are spinlock, several nonatomic operations, spin_unlock.
Right, and it is the spinlock that is the problem. See discussions a
few months back: at least on Intel SMP machines, most of the problem
seems to have to do with trading the spinlock's cache line back and
forth between CPUs. It's difficult to see how a futex is going to avoid
that.
regards, tom lane
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Dave Cramer
www.postgresintl.com
519 939 0336
ICQ#14675561
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