Messages in this thread | | | Date | Tue, 28 Mar 2017 16:29:13 +0900 | From | Byungchul Park <> | Subject | Re: [PATCH 0/8] sched/deadline: Return the best satisfying affinity and dl in cpudl_find |
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On Tue, Mar 28, 2017 at 08:11:53AM +0100, Juri Lelli wrote: > > > > For example: > > > > > > > > cpu 0 is running a task (dl: 10). > > > > cpu 1 is running a task (dl: 9). > > > > cpu 2 is running a task (dl: 8). > > > > cpu 3 is running a task (dl: 2). > > > > > > > > where cpu 3 want to push a task (affinity is 1 2 3 and dl is 1). > > > > > > Hummm, but this should only happen if you disable admission control, > > > right? Otherwise task's affinity can't be smaller that 0-3. > > > > Hi Juri, > > > > Can I ask you what is addmission control? Do you mean affinity setting? > > sched_setattr() for DEADLINE tasks peforms a set of checks before > admitting the task to the system. Please have a look at Documentation/ > scheduler/sched-deadline.txt::Section5 for what concerns affinity.
I see.
> > And do you mean s/disable/enable? Or am I misunderstanding? > > > > No, I meant disable. The problem is that if you disable admission > control the problem you are pointing out can happen, if admission > control is enabled otherwise it can't, as we enforce that tasks have > affinity equal to the root_domain span to which they belong. E.g, in > your case the task will have affinity set to 0-3 (or it won't be able to > enter the system), so that would make the problem go away.
I see.
> > > > In this case, the task should be migrated from cpu 3 to cpu 1, and > > > > preempt cpu 1's task. However, current code just returns fail because > > > > it fails at the affinity test with the maximum cpu, that is, cpu 0. > > > > > > > > This patch set tries to find the best among ones satisfying task's > > > > affinity and dl constraint until success or no more to see. > > > > > > > > > > Anyway, do you have numbers showing how common is you fail scenario? > > > > Actually, it very depends on how to set test environment. I can provide > > you ones which generate many fails. IMHO, it's not a matter of frequency > > but a matter of whether it works corrently. As you know, rt policy already > > works corrently regarding this problem. > > > > Right. But, my point is that if what you are highlighting turns out to > be a pretty frequent situation, maybe we need to find a better data > structure to speed up push operations or we will end up using the slow > path most of the times, making the heap useless.
I totally agree with you. I will check it and let you know.
Thank you, Byungchul
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