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From Aaron Bannert <aa...@clove.org>
Subject Re: More worker ideas Re: cvs commit: httpd-2.0/server/mpm/worker worker.c fdqueue.c fdqueue.h
Date Sun, 28 Apr 2002 03:24:29 GMT
On Sat, Apr 27, 2002 at 07:39:24PM -0700, Brian Pane wrote:
> I was going to complain about the addition of yet another mutex
> to the critical path of request processing, but it got me thinking
> about an approach to making worker faster: shorten the time spent
> in the mutex-protected region.

Yes! The other neat thing about this is we get to balance the
critical path between two mutex regions, rather than one_big_mutex.

> By shortening the code path between the lock and the unlock, we
> can reduce the probability that two or more threads will be
> contending for the mutex at once.  And uncontended mutexes have
> a lot less overhead.
> 
> I'm going to experiment with streamlining the code within the
> mutex-protected blocks of the fdqueue functions to see how much
> it helps the multiprocessor performance.  At first glance, the
> candidates for optimization are:
>   * In the case where we can't recycle a pool in ap_queue_pop(),
>     move the destruction of the pool *outside* the mutex-protected
>     block.
>   * Maybe change the queue size to a power of two so that we can
>     replace the modulo operations with a bit mask.

++1 on both accounts. I was also thinking that we could make the queue
elements simple pointers, rather than 2 elements in a structure. That
way the element lookups can happen outside of the mutex region, and
inside we can have a simple struct* assignment.

-aaron

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