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SubjectRe: smpnice loadbalancing with high priority tasks
Peter Williams wrote:
> Siddha, Suresh B wrote:
>>>> c) DP system: if the cpu-0 has two high priority and cpu-1 has one
>>>> normal
>>>> priority task, how can the current code detect this imbalance..
>>> How would it not?
>>
>> imbalance will be always < busiest_load_per_task and
>> max_load - this_load will be < 2 * busiest_load_per_task...
>> and pwr_move will be <= pwr_now...
>
> I had thought about substituting (busiest_load_per_task +
> this_load_per_task) for (busiest_load_per_task * 2) but couldn't
> convince myself that it was the right thing to do. (The final update to
> this_load_per_task would need to be moved.) The reason I couldn't
> convince myself is that I thought it might be too aggressive and cause
> excessive balancing. Maybe something more sophisticated is needed to
> prevent that possibility. It should be noted that the relative sizes of
> busiest_load_per_task and this_load_per_task my be useful in deciding
> what to do in these cases. I'll put some thought into that.

How does this bit of code look?

if (busiest_load_per_task > this_load_per_task) {
if (max_load - this_load > busiest_load_per_task) {
*imbalance = busiest_load_per_task;
return busiest;
}
} else if (max_load - this_load >= busiest_load_per_task*2) {
*imbalance = busiest_load_per_task;
return busiest;
}

My maths indicate this will work even in cases when the difference
between the two load per task values is small. By "work" I mean that it
will one of the high priority tasks and it won't bounce back. Do you agree?

The actual patch would be a little neater than this, of course.

Peter
--
Peter Williams pwil3058@bigpond.net.au

"Learning, n. The kind of ignorance distinguishing the studious."
-- Ambrose Bierce
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