Re: [PATCH v3 05/22] sched: remove domain iterations infork/exec/wake

[li guang]

å 2013-01-11äç 10:07 +0000ïMorten Rasmussenåéï
> On Fri, Jan 11, 2013 at 02:46:31AM +0000, Alex Shi wrote:
> > On 01/10/2013 02:21 AM, Morten Rasmussen wrote:
> > >>  		new_cpu = find_idlest_cpu(group, p, cpu);
> > >> > -
> > >> > -		/* Now try balancing at a lower domain level of new_cpu */
> > >> > -		cpu = new_cpu;
> > >> > -		weight = sd->span_weight;
> > >> > -		sd = NULL;
> > >> > -		for_each_domain(cpu, tmp) {
> > >> > -			if (weight <= tmp->span_weight)
> > >> > -				break;
> > >> > -			if (tmp->flags & sd_flag)
> > >> > -				sd = tmp;
> > >> > -		}
> > >> > -		/* while loop will break here if sd == NULL */
> > > I agree that this should be a major optimization. I just can't figure
> > > out why the existing recursive search for an idle cpu switches to the
> > > new cpu near the end and then starts a search for an idle cpu in the new
> > > cpu's domain. Is this to handle some exotic sched domain configurations?
> > > If so, they probably wouldn't work with your optimizations.
> > 
> > I did not find odd configuration that asking for old logical.
> > 
> > According to Documentation/scheduler/sched-domains.txt, Maybe never.
> > "A domain's span MUST be a superset of it child's span (this restriction
> > could be relaxed if the need arises), and a base domain for CPU i MUST
> > span at least i."  etc. etc.
> 
> The reason for my suspicion is the SD_OVERLAP flag, which has something
> to do overlapping sched domains. I haven't looked into what it does or
> how it works. I'm just wondering if this optimization will affect the
> use of that flag.

seems it did, SD_OVERLAP will not work after this change,
though this flag is maybe scarcely used.
because, this optimization assume all sched-domains span 
is super-set over child domain.
isn't it? Alex.

> 
> Morten
> 
> > 
> > 
> > -- 
> > Thanks Alex
> > 
> 
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-- 
regards!
li guang

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