Messages in this thread | | | Date | Thu, 4 Apr 2013 09:42:31 +0900 | From | Joonsoo Kim <> | Subject | Re: [PATCH 4/5] sched: don't consider upper se in sched_slice() |
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Hello, Preeti.
On Tue, Apr 02, 2013 at 11:02:43PM +0530, Preeti U Murthy wrote: > Hi Joonsoo, > > > >>> I think that it is real problem that sysctl_sched_min_granularity is not > >>> guaranteed for each task. > >>> Instead of this patch, how about considering low bound? > >>> > >>> if (slice < sysctl_sched_min_granularity) > >>> slice = sysctl_sched_min_granularity; > >> > >> Consider the below scenario. > >> > >> A runqueue has two task groups,each with 10 tasks. > >> > >> With the current implementation,each of these tasks get a sched_slice of > >> 2ms.Hence in a matter of (10*2) + (10*2) = 40 ms, all tasks( all tasks > >> of both the task groups) will get the chance to run. > >> > >> But what is the scheduling period in this scenario? Is it 40ms (extended > >> sysctl_sched_latency), which is the scheduling period for each of the > >> runqueues with 10 tasks in it? > >> Or is it 80ms which is the total of the scheduling periods of each of > >> the run queues with 10 tasks.Either way all tasks seem to get scheduled > >> atleast once within the scheduling period.So we appear to be safe. > >> Although the sched_slice < sched_min_granularity. > >> > >> With your above lower bound of sysctl_sched_min_granularity, each task > >> of each tg gets 4ms as its sched_slice.So in a matter of > >> (10*4) + (10*4) = 80ms,all tasks get to run. With the above question > >> being put forth here as well, we don't appear to be safe if the > >> scheduling_period is considered to be 40ms, otherwise it appears fine to > >> me, because it ensures the sched_slice is atleast sched_min_granularity > >> no matter what. > > > > So, you mean that we should guarantee to schedule each task atleast once > > in sysctl_sched_latency? > > I would rather say all tasks get to run atleast once in a sched_period, > which could be just sysctl_sched_latency or more depending on the number > of tasks in the current implementation. > > But this is not guaranteed in current code, > > this is why I made this patch. Please refer a patch description. > > Ok,take the example of a runqueue with 2 task groups,each with 10 > tasks.Same as your previous example. Can you explain how your patch > ensures that all 20 tasks get to run atleast once in a sched_period?
My patch doesn't ensure that :) I just want to say a problem of current implementation which can't ensure to run atleast once in sched_period through my patch description.
So, how about extending a sched_period with rq->nr_running, instead of cfs_rq->nr_running? It is my quick thought and I think that we can ensure to run atleast once in this extending sched_period.
And, do we leave a problem if we cannot guaranteed atleast once property?
Thanks.
> > Regards > Preeti U Murthy > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/
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