Re: LWLock contention: I think I understand the problem

Tom Lane wrote:
> I have thought of a further refinement to the patch I produced
> yesterday.  Assume that there are multiple waiters blocked on (eg)
> BufMgrLock.  After we release the first one, we want the currently
> running process to be able to continue acquiring and releasing the lock
> for as long as its time quantum holds out.  But in the patch as given,
> each acquire/release cycle releases another waiter.  This is probably
> not good.
> 
> Attached is a modification that prevents additional waiters from being
> released until the first releasee has a chance to run and acquire the
> lock.  Would you try this and see if it's better or not in your test
> cases?  It doesn't seem to help on a single CPU, but maybe on multiple
> CPUs it'll make a difference.
> 
> To try to make things simple, I've attached the mod in two forms:
> as a diff from current CVS, and as a diff from the previous patch.

This does seem like a nice optimization.  I will try to test it tomorrow
but I doubt I will see any change on BSD/OS.

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