Re: [Chicken-hackers] PATCH: more efficient scheduler

[Andy Bennett]

Hi Jörg,

Do you think this patch would affect the issue I was seeing in my 2015
mail to chicken-users "http-client gets stuck in scheduler when reusing
connect"?
(https://lists.gnu.org/archive/html/chicken-users/2015-06/msg00056.html )




> the attached patch does not fix any bugs.  It brings some performance
> improvements under certain load conditions.  The cost: It adds the
> overhead of another counter and a dispatch on a a fixnum modulo
> operation - IMHO negotiable.
> 
> The change is helpful when sits watching on several file descriptors for
> requests _and_ uses several threads, message passing etc. to produce
> responses.
> 
> Under these circumstances I found a common call pattern to be few file
> descriptors to become available resulting in many internal threads
> forked.  Those threads have often very little actual work to do until
> the block again.  At this point each ##sys#schedule will check those
> file descriptors again and again - typically not returning any fd until
> after all those threads completed eventually.  This results in a pretty
> huge delay of the response.
> 
> With the change there is now a "pending-queue".  This holds all the
> threads to be run once before we even check for new work from timeouts
> or i/o.  Furthermore we only check for i/o at an adjustable rate or if
> we would wait otherwise.
> 
> I have a test case where there are about 50 threads waiting on input and
> observed up to 200 in state "ready" to pass messages among each other at
> a time.  Those saved i/o times add up to a difference of about 30%
> faster responses.
> 
> Best
> 
> /Jörg
> 
> 
> 
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Regards,
@ndy

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