[Dovecot] load increase after upgrade to 2.0.8

Stan Hoeppner stan at hardwarefreak.com
Fri Dec 10 11:46:29 EET 2010

Ralf Hildebrandt put forth on 12/10/2010 1:39 AM:
> * Timo Sirainen <tss at iki.fi>:
>> Cor's debugging has so far shown that a single epoll_wait() call can
>> sometimes generate a few thousand voluntary context switches. I can't
>> really understand how that's possible. Those epoll_wait() calls about
>> half of the total voluntary context switches generated by imap
>> processes. We'll see tomorrow if poll() works better or if a small
>> patch I made makes it better.
> That sounds promising :)

Has anyone considered a compiler issue?  A gcc optimization flags issue?
 A gcc version issue?  Something along these lines?

To generate the number of context switches/sec that has been mentioned,
that would seem to indicate a fast loop running more times than it
should but without actually doing much, thus not utilizing its full time
slice, getting sidelined by the scheduler, but ready to run on each
kernel tick.  Thus it runs on each kernel tick.  Could something like
"-funroll-all-loops" be having problems with the 2.0.x source?

I'm talking a bit out of my element here.  I know just enough about
compiler technology and machine code to make me really dangerous, but
not very useful. :)  I'm just trying to look outside the box I guess, or
leave no stone unturned.  Pick you favorite analogy that applies.

Cor and Ralf, are you two using the same gcc version?  Same flags?  Are
they different than the switches/flags most other 2.0.x OPs are using
when they make the source?


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