[Dovecot] load increase after upgrade to 2.0.8

Ralf Hildebrandt Ralf.Hildebrandt at charite.de
Thu Dec 9 21:13:09 EET 2010

* Mark Moseley <moseleymark at gmail.com>:

> > We're on 2.6.32 and the load only goes up when I change dovecot (not
> > when I change the kernel, which I didn't do so far)
> If you at some point upgrade to >2.6.35, I'd be interested to hear if
> the load skyrockets on you.

You mean even more? I'm still hoping it would decrease at some point :)
I updated to 2.6.32-27-generic-pae today. I wonder what happens.

> I also get the impression that the load average calculation in these
> recent kernels is 'touchier' than in pre-2.6.35. Even with similar CPU
> and I/O utilization, the load average on a >2.6.35 both is much higher
> than pre- and it also seems to react more quickly; more jitter I guess.
> That's based on nothing scientific though.


> Upping the client_limit actually results in less processes, since a
> single process can service up to #client_limit connections. When I
> bumped up the client_limit for imap, my context switches plummeted.

Which setting are you using now?

> Though as Timo pointed out on another thread the other day when I was
> asking about this, when that proc blocks on I/O, it's blocking all the
> connections that the process is servicing.Timo, correct me if I'm
> wildly off here -- I didn't even know this existed before a week or
> two ago. So you can then end up creating a bottleneck, thus why I've
> been playing with finding a sweet spot for imap.

Blocking on /proc? Never heard that before.

> I figure that enough of a process's imap connections must be sitting in
> IDLE at any given moment, so setting client_limit to like 4 or 5 isn't
> too bad. Though it's not impossible that by putting multiple
> connections on a single process, I'm actually throttiling the system,
> resulting in fewer context switches (though I'd imagine bottlenecked
> procs would be blocked on I/O and do a lot of volcs's).

Ralf Hildebrandt
  Geschäftsbereich IT | Abteilung Netzwerk
  Charité - Universitätsmedizin Berlin
  Campus Benjamin Franklin
  Hindenburgdamm 30 | D-12203 Berlin
  Tel. +49 30 450 570 155 | Fax: +49 30 450 570 962
  ralf.hildebrandt at charite.de | http://www.charite.de

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