Re: [PATCH v3] sched/deadline: overrun could happen in start_hrtick_dl

[xiaofeng.yan]

On 2014/8/12 22:52, Ingo Molnar wrote:
> * xiaofeng.yan <xiaofeng.yan@xxxxxxxxxx> wrote:
>
> > It could be wrong for the precision of runtime and deadline
> > when the precision is within microsecond level. For example:
> > Task runtime deadline period
> >   P1   200us   500us   500us
> >
> > This case need enbale HRTICK feature by the next command
> >
> > PC#echo "HRTICK" > /sys/kernel/debug/sched_features
> > PC#trace-cmd record -e sched_switch &
> > PC#./schedtool -E -t 200000:500000 -e ./test
> >
> > Some of runtime and deadline run with millisecond level by
> > reading kernershark. Some pieces of trace.dat are as follows:
> > (remove some irrelevant information)
> > <idle>-0   157.603157: sched_switch: :R ==> 2481:4294967295: test
> > test-2481  157.603203: sched_switch:  2481:R ==> 0:120: swapper/2
> > <idle>-0   157.605657: sched_switch:  :R ==> 2481:4294967295: test
> > test-2481  157.608183: sched_switch:  2481:R ==> 2483:120: trace-cmd
> > trace-cmd-2483 157.609656: sched_switch:2483:R==>2481:4294967295: test
> >
> > We can get the runtime from the information at some point.
> > runtime = 157.605657 - 157.608183
> > runtime = 0.002526(2.526ms)
> > The correct runtime should be less than or equal to 200us at some point.
> >
> > The problem is caused by a conditional judgment "delta > 10000".
> > Because no hrtimer start up to control the runtime when runtime is less than 10us.
> > So the process will continue to run until tick-period coming.
> >
> > Move the code with the limit of the least time slice
> > from hrtick_start_fair() to hrtick_start() because
> > EDF schedule class also need this function in start_hrtick_dl().
> >
> > To fix this problem, we call hrtimer_start() unconditionally in start_hrtick_dl(),
> > and make sure schedule slice won't be smaller than 10us in hrtimer_start().
> >
> > Signed-off-by: Xiaofeng Yan <xiaofeng.yan@xxxxxxxxxx>
> > Reviewed-by:   Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> > Reviewed-by:   Li Zefan <lizefan@xxxxxxxxxx>
> The whole changelog is very hard to read and isn't proper English, nor
> is it truly explanatory. Could you please fix the changelog, or bounce
> it to someone who will fix it for you?
>
> Thanks,
>
> 	Ingo

Thanks for your reply. I will fix my change log with proper English.
Thanks
Yan
> .


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