Martin Bligh wrote:
But I was thinking more about the code that (in the original) handled
the case where the number of tasks to be moved was less than 1 but
more than 0 (i.e. the cases where "imbalance" would have been reduced
to zero when divided by SCHED_LOAD_SCALE). I think that I got that
part wrong and you can end up with a bias load to be moved which is
less than any of the bias_prio values for any queued tasks (in
circumstances where the original code would have rounded up to 1 and
caused a move). I think that the way to handle this problem is to
replace 1 with "average bias prio" within that logic. This would
guarantee at least one task with a bias_prio small enough to be moved.
I think that this analysis is a strong argument for my original patch
being the cause of the problem so I'll go ahead and generate a fix.
I'll try to have a patch available later this morning.
Attached is a patch that addresses this problem. Unlike the
description above it does not use "average bias prio" as that solution
would be very complicated. Instead it makes the assumption that
NICE_TO_BIAS_PRIO(0) is a "good enough" for this purpose as this is
highly likely to be the median bias prio and the median is probably
better for this purpose than the average.
Signed-off-by: Peter Williams <[email protected]>
Doesn't fix the perf issue.
OK, thanks. I think there's a few more places where SCHED_LOAD_SCALE
needs to be multiplied by NICE_TO_BIAS_PRIO(0). Basically, anywhere
that it's added to, subtracted from or compared to a load. In those
cases it's being used as a scaled version of 1 and we need a scaled
version of NICE_TO_BIAS_PRIO(0). I'll have another patch later today.
Peter
--
Peter Williams [email protected]
"Learning, n. The kind of ignorance distinguishing the studious."
-- Ambrose Bierce
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