Tuning the scheduler? Desktop with a CPU-intensive task becomes rapidly unusable.

jan.grant at bristol.ac.uk jan.grant at bristol.ac.uk
Thu Sep 2 10:46:17 UTC 2010

On Thu, 2 Sep 2010, Andriy Gapon wrote:

> on 02/09/2010 12:08 jan.grant at bristol.ac.uk said the following:
> > On Wed, 1 Sep 2010, Ivan Voras wrote:
> > 
> >> On 09/01/10 15:08, jan.grant at bristol.ac.uk wrote:
> >>> I'm running -STABLE with a kde-derived desktop. This setup (which is
> >>> pretty standard) is providing abysmal interactive performance on an
> >>> eight-core machine whenever I try to do anything CPU-intensive (such as
> >>> building a port).
> >>>
> >>> Basically, trying to build anything from ports rapidly renders everything
> >>> else so "non-interactive" in the eyes of the scheduler that, for instance,
> >>> switching between virtual desktops (I have six of them in reasonably
> >>> frequent use) takes about a minute of painful waiting on redraws to
> >>> complete.
> >>
> >> Are you sure this is about the scheduler or maybe bad X11 drivers?
> > 
> > Not 100%, but mostly convinced; I've just started looking at this. It's my 
> > first stab at what might be going on. X11 performance is usually pretty 
> > snappy. There's no paging pressure at all.
> From my experience:
> 1. system with Athlon II X2 250 CPU and onboard AMD graphics - no issues with
> interaction between buildworld and GUI with all KDE4 effects enabled (OpenGL).
> 2. system with comparable Core2 Duo CPU and onboard Intel graphics (G33) -
> enabling OpenGL desktop effects in KDE4 leads to the consequences like what you
> describe.  With all GUI bells and whistles disabled the system behaves quite
> like the AMD system.

All desktop effects are disabled. The graphics are from an nVidia GeForce 
8500 GT (G86) with the X.org driver. (It's not _just_ desktop behaviour 
that's affected, though: the box runs a number of small headless 
[interactive] server processes which also appear to get rapidly starved of 
CPU time.)

The behaviour isn't visible with the 4bsd scheduler; "stuff" generally 
remains snappy and responsive.

I'll keep poking around and see if I can get to the bottom of it.

jan grant, ISYS, University of Bristol. http://www.bris.ac.uk/
Tel +44 (0)117 3317661   http://ioctl.org/jan/
Rereleasing dolphins into the wild since 1998.

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