idprio processes slowing down system

[Adam Vande More]

On Sun, Nov 28, 2010 at 1:26 AM, Peter Jeremy <peterjeremy at acm.org> wrote:

> Since all the boinc processes are running at i31, why are they impacting
> a buildkernel that runs with 0 nicety?
>

Someone please enlighten me if I'm wrong, but I'll take a stab at it.

With the setup you presented you're going to have a lot of context switches
as the buildworld is going to give plenty of oppurtunities for boinc
processes to get some time.  When it does switch out, the CPU cache is
invalidated, then invalidated again when the buildworld preempts back.  This
is what makes it slow.  If gcc was building one massive binary at that
priority, you wouldn't have boinc getting much/any time.  Since the
buildworld is much more modular and consists of a large amount of small
operations some CPU intentisive, some IO intensive, boinc can interrupt and
impact overall performance even if the inital process was started at a much
higher priority.

I'm not sure how well ULE handles CPU affinity.  Some other stuff I ran into
earlier suggested there's room for improvement, but in your particular use
case I'm not sure even ideal CPU affinity would improve things much.

-- 
Adam Vande More