Messages in this thread |  | | Date | Wed, 16 Aug 2017 11:17:36 +0900 | From | Byungchul Park <> | Subject | Re: [PATCH v6 1/2] sched/deadline: Add support for SD_PREFER_SIBLING on find_later_rq() |
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On Tue, Aug 15, 2017 at 09:42:01PM -0400, Steven Rostedt wrote: > > > > @@ -1385,6 +1407,17 @@ static int find_later_rq(struct task_struct *task) > > > > * already under consideration through later_mask. > > > > */ > > > > if (best_cpu < nr_cpu_ids) { > > > > + /* > > > > + * If current domain is SD_PREFER_SIBLING > > > > + * flaged, we have to get more chances to > > > > + * check other siblings. > > BTW, "we have to get more chances" doesn't really make sense. Do you > mean "we need to try other domains"?
Yes, we need to try other domains first if current domain is SD_PREFER_SIBLING flaged.
> > > > + */ > > > > + if (sd->flags & SD_PREFER_SIBLING) { > > > > + prefer = sd; > > > > > > Is this how the SD_PREFER_SIBLING works? According to this, the > > > preferred sd is the next sd in for_each_domain(). Not to mention, the > > > prefer variable stays set if the next domain has no available CPUs. Is > > > that what we want? > > > > Maybe I don't understand what you want to say. The variable, prefer, is > > used to pick up the smallest sched domain among SD_PREFER_SIBLING > > domains, if more than one SD_PREFER_SIBLING domain exist in the visit. > > > > The prefer variable alway points to the previous SD_PREFER_SIBLING domain. > > And that must stay set to be used as a fallback choise if the next domain > > has no available CPUs. > > > > Could you explain what I mis-understand? > > > > I may be the one confused here ;-) > > I think I misread the patch. So, the SD_PREFER_SIBLING means to try to > find a CPU in another sd instead? Thus, we try to find a CPU in a sd > that does not have SD_PREFER_SIBLING set. And if there is none, we use > the preferred sd as a fallback. Is that correct?
Yes, that's what I intended. IOW:
If (we found a proper sd, not having SD_PREFER_SIBLING?) use the sd; else if (we found a proper sd, having SD_PREFER_SIBLING?) use the smallest sd among SD_PREFER_SIBLING sds;
Thanks, Byungchul
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