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SubjectRe: CPU affinity

On Thu, 15 Apr 1999, Richard Gooch wrote:

> It looks to me that the underlying problem is that xosview steals the
> CPU that the number cruncher is running on, instead of using the other
> CPU (which I presume is idle). That shouldn't happen. If it does, it's
> a bug.

this is not a bug, it's because xosview is an 'interactive' process, and
such it has higher priority. (and the right to kick a lowprio process out,
especially if xosview ran on that CPU previously). Btw., xosview's active
timeslice is several msecs on a typical SMP box, so this is definitely not
an outright bad decision by the scheduler.

i have the plan to do per-process and per-CPU 'cache-set tracking' via
performance counters in 2.3 (basically what you see in 2.2 is already a
variant of this). That one has a chance to weigh a process's priority with
it's active cachesize.

anyway, even with 2.2.5 the expected behavior is that the number-cruching
process settles on one CPU after some initial ping-pong, and xosview
settles on some other CPU. If this does not happen _thats_ a bug. Anyway,
be careful with xosview, it's obviously a bit tricky to measure scheduling
with a tool that itself is rather intrusive as well ...

-- mingo


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