Re: [rfc][patch] sched: remove smpnice

[Peter Williams <pwil3058@bigpond.net.au>]

Peter Williams wrote:
> Andrew Morton wrote:
> 
>> "Siddha, Suresh B" <suresh.b.siddha@intel.com> wrote:
>>
>>> b) On a lightly loaded system, this can result in HT scheduler 
>>> optimizations
>>> being disabled in presence of low priority tasks... in this case, 
>>> they(low
>>> priority ones) can end up running on the same package, even in the 
>>> presence of other idle packages.. Though this is not as serious as 
>>> "a" above...
>>>
> 
> I think that this issue comes under the heading of "Result of better 
> nice enforcement" which is the purpose of the patch :-).

On the assumption that this enforcement is considered to be too 
vigorous,  I think that it is also amenable to a fix based on a new 
biased_load() function by replacing the (*imbalance < SCHED_LOAD_SCALE) 
test with (biased_load(*imbalance, busiest) == 0) and (possibly) some 
modifications within the if statement's body (most notably replacing the 
NICE_TO_BIAS_PRIO(0) expressions with (busiest->prio_bias / 
busiest->nr_running) or something similar).

This change would cause no change in functionality in the case where all 
tasks are nice==0.

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

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