Messages in this thread |  | | Date | Tue, 15 Aug 2017 21:42:01 -0400 | From | Steven Rostedt <> | Subject | Re: [PATCH v6 1/2] sched/deadline: Add support for SD_PREFER_SIBLING on find_later_rq() |
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On Wed, 16 Aug 2017 09:38:11 +0900 Byungchul Park <byungchul.park@lge.com> wrote:
> On Tue, Aug 15, 2017 at 11:19:40AM -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"?
> > > + */ > > > + 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?
I'm not familiar with the SD_PREFER_SIBLING flag, the only documentation I can find about it is the comment that states:
/* Prefer to place tasks in a sibling domain */
And the very informative git commit change log:
commit b5d978e0c7e79a7ff842e895c85a86b38c71f1cd Date: Tue Sep 1 10:34:33 2009 +0200
sched: Add SD_PREFER_SIBLING Do the placement thing using SD flags.
;-)
-- Steve
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