Messages in this thread | | | Date | Fri, 21 Jun 2013 10:57:27 +0800 | Subject | Re: [patch v8 3/9] sched: set initial value of runnable avg for new forked task | From | Lei Wen <> |
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Morten,
On Thu, Jun 20, 2013 at 6:23 PM, Morten Rasmussen <morten.rasmussen@arm.com> wrote: > On Sat, Jun 15, 2013 at 01:09:12PM +0100, Lei Wen wrote: >> On Fri, Jun 14, 2013 at 9:59 PM, Alex Shi <alex.shi@intel.com> wrote: >> > On 06/14/2013 06:02 PM, Lei Wen wrote: >> >>> > enqueue_entity >> >>> > enqueue_entity_load_avg >> >>> > >> >>> > and make forking balancing imbalance since incorrect load_avg_contrib. >> >>> > >> >>> > Further more, Morten Rasmussen notice some tasks were not launched at >> >>> > once after created. So Paul and Peter suggest giving a start value for >> >>> > new task runnable avg time same as sched_slice(). >> >> I am confused at this comment, how set slice to runnable avg would change >> >> the behavior of "some tasks were not launched at once after created"? >> > >> > I also don't know the details on Morten's machine. but just guess, there >> > are much tasks on in the run queue. the minimum load avg make the new >> > task wait its time... >> >> Is there some possibility that since task structure is allocated without being >> set to 0, and it cause the imbalance between runqueues. Then the new forked >> is migrated to other cpus, so that it cause its execution being delayed? >> >> It is better for Morten to give us more details here. :) >> > > I think Peter's reply pretty much covers it. The problem is when a task > is not running (other task has lower vruntime or blocked for other > reasons) shortly after the task was created. The runnable_avg_period is > very small, so the load_contrib is very sensitive. > > Say if a task runs for 1 ms then is blocked for 1 ms and then runs > again, the load_contrib will go from 100% to 50% instantly and then ramp > back up again. So the task load may be quite different from the true > load of the task depending on when you calculate the load_contrib. > > Preloading runnable_avg_period should make the load_contrib a little > less sensitive to this behaviour.
Thanks for detailed explanation! Now I could understand the preloading value prevent entity's load change quickly at its beginning. But I cannot see why this could explain "some tasks were not launched at once after created"
Or should I understand the previous words as: "If without preloading value, the new created task's contributed load may vary too quickly at its beginning. Like if a task runs for 1 ms then is blocked for 1 ms and then runs again, the load_contrib will go from 100% to 50% instantly."
Thanks, Lei
> > Morten > >> Thanks, >> Lei >> >> >> >> >> IMHO, I could only tell that for the new forked task, it could be run if current >> >> task already be set as need_resched, and preempt_schedule or >> >> preempt_schedule_irq >> >> is called. >> >> >> >> Since the set slice to avg behavior would not affect this task's vruntime, >> >> and hence cannot make current running task be need_sched, if >> >> previously it cannot. >> >> >> >> Could you help correct if I am wrong at somewhere? .... >> >> >> >> Thanks, >> > >> > >> > -- >> > Thanks >> > Alex >> >
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