Re: bad interactive performance when building

[Matthew Mondor <mm_lists%pulsar-zone.net@localhost>]

On Wed, 25 Feb 2009 17:00:42 +0200
Antti Kantee <pooka%cs.hut.fi@localhost> wrote:

> Has anyone noticed that the UI slows down considerably on 5.0 when
> building with a high enough -j and doing something which consumes a
> little CPU for UI processes (e.g. minimize/maximize a web browser).
> This happens both with 4BSD and M2.  I never saw it on 4.99.42.
> 
> I realize this may be simply because 5.0 is faster, but I don't know if
> we can call it progress if a faster system feels slower to the user.

A potential problem I could see is resource starvation, i.e. too many
threads using too much CPU time and not leaving enough for the single
thread handling a particular GUI utility...  If this is the case,
starting make(1) with nice(1), causing children processes to inherit
the priority, should help a lot.  Another tip might be to raise/lower
the priority of the login class used by interactive applications users.

With the current 1:1 thread cpu cycles scheduler. I think that all LWPs
are treated equal independent of the process they pertain to, other
than CPU afinity and the priority, so this would be quite equivalent to
running as many non-idle processes as you use for -j on netbsd-4 or
netbsd-5, which might likewise degrade performance of normal priority
GUI applications?

I've not really checked on netbsd-5, but usually non-idle processes'
priority is raised automatically for processes which don't idle for a
certain time.  If this is not the same for LWPs this could also be a
potential issue.  Or perhaps they aren't raised aggressively enough?
-- 
Matt