On Fri, 2019-07-05 at 16:51 +0200, Vincent Guittot wrote: > On Fri, 28 Jun 2019 at 22:49, Rik van Riel <[email protected]> wrote: > > The way the time slice length is currently calculated, not only do > > high > > priority tasks get longer time slices than low priority tasks, but > > due > > to fixed point math, low priority tasks could end up with a zero > > length > > time slice. This can lead to cache thrashing and other > > inefficiencies. > > > > Simplify the logic a little bit, and cap the minimum time slice > > length > > to sysctl_sched_min_granularity. > > > > Tasks that end up getting a time slice length too long for their > > relative > > priority will simply end up having their vruntime advanced much > > faster than > > other tasks, resulting in them receiving time slices less > > frequently. > > > > Signed-off-by: Rik van Riel <[email protected]> > > --- > > kernel/sched/fair.c | 25 ++++++++----------------- > > 1 file changed, 8 insertions(+), 17 deletions(-) > > > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > > index d48bff5118fc..8da2823401ca 100644 > > --- a/kernel/sched/fair.c > > +++ b/kernel/sched/fair.c > > @@ -671,22 +671,6 @@ static inline u64 calc_delta_fair(u64 delta, > > struct sched_entity *se) > > return delta; > > } > > > > -/* > > - * The idea is to set a period in which each task runs once. > > - * > > - * When there are too many tasks (sched_nr_latency) we have to > > stretch > > - * this period because otherwise the slices get too small. > > - * > > - * p = (nr <= nl) ? l : l*nr/nl > > - */ > > -static u64 __sched_period(unsigned long nr_running) > > -{ > > - if (unlikely(nr_running > sched_nr_latency)) > > - return nr_running * sysctl_sched_min_granularity; > > - else > > - return sysctl_sched_latency; > > -} > > - > > /* > > * We calculate the wall-time slice from the period by taking a > > part > > * proportional to the weight. > > @@ -695,7 +679,7 @@ static u64 __sched_period(unsigned long > > nr_running) > > */ > > static u64 sched_slice(struct cfs_rq *cfs_rq, struct sched_entity > > *se) > > { > > - u64 slice = __sched_period(cfs_rq->nr_running + !se- > > >on_rq); > > + u64 slice = sysctl_sched_latency; > > Is the change above and the remove of __sched_period() really needed > for fixing the null time slice problem ? > This change impacts how tasks will preempt each other and as a result > the throughput. It should have it dedicated patch so we can evaluate > its impact
Good point. I will split this up into two patches for v3. Thank you. -- All Rights Reversed.
signature.asc
Description: This is a digitally signed message part
