Re: [patch v8 6/9] sched: compute runnable load avg in cpu_load andcpu_avg_load_per_task

From: Alex Shi
Date: Wed Jun 19 2013 - 20:34:48 EST

On 06/19/2013 04:15 PM, Alex Shi wrote:
> On 06/18/2013 05:44 PM, Alex Shi wrote:
>>> Paul, could I summary your point here:
>>> keep current weighted_cpu_load, but add blocked load avg in
>>> get_rq_runnable_load?
>>> I will test this change.
>> Current testing(kbuild, oltp, aim7) don't show clear different on my NHM EP box
>> between the following and the origin patch,
>> the only different is get_rq_runnable_load added blocked_load_avg. in SMP
>> will test more cases and more box.
> I tested the tip/sched/core, tip/sched/core with old patchset and
> tip/schec/core with the blocked_load_avg on Core2 2S, NHM EP, IVB EP,
> SNB EP 2S and SNB EP 4S box, with benchmark kbuild, sysbench oltp,
> hackbench, tbench, dbench.
> blocked_load_avg VS origin patchset, oltp has suspicious 5% and
> hackbench has 3% drop on NHM EX; dbench has suspicious 6% drop on NHM
> EP. other benchmarks has no clear change on all other machines.
> origin patchset VS sched/core, hackbench rise 20% on NHM EX, 60% on SNB
> EP 4S, and 30% on IVB EP. others no clear changes.

>> +#ifdef CONFIG_SMP
>> +unsigned long get_rq_runnable_load(struct rq *rq)
>> +{
>> + return rq->cfs.runnable_load_avg + rq->cfs.blocked_load_avg;

According to above testing result, with blocked_load_avg is still a
slight worse than without it.

when the blocked_load_avg added here, it will impact nohz idle balance
and periodic balance in update_sg_lb_stats() when the idx is not 0.
As to nohz idle balance, blocked_load_avg should be too small to have
big effect.
As to in update_sg_lb_stats(), since it only works when _idx is not 0,
that means the blocked_load_avg was decay again in update_cpu_load. That
reduce its impact.

So, could I say, at least in above testing, blocked_load_avg should be
keep away from balance?

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