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

[Peter Bex]

On Mon, Feb 15, 2016 at 01:57:52PM +0100, Jörg F. Wittenberger wrote:
> Hi,
> 
> 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.

Hi Joerg,

I've tested with some varying types of load with Spiffy (using wrk, ab
and siege).  The results are inconclusive either way.  The patch doesn't
seem to make much of a difference, at least with a reasonably simple
Spiffy setup.

This is quite an invasive patch, which moves whole swaths of code and
also complicates the scheduler further by adding more lists and tweaks,
and even removes some things like the check for C_signal_interrupted_p,
which makes me very hesitant to just apply it for an alleged performance
boost.  On the whole, I think it's too dangerous to fiddle with the
scheduler unless it brings either considerable simplification of the
scheduler's code, or measurable improvements for common workloads.

Also, you did mention getting segfaults with your version, so who's
to say this change doesn't *introduce* any segfault crashes?

So, unless you can show us how to reproduce this measured improvement,
I think it's best not to apply this patch.

Cheers,
Peter

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