Messages in this thread Patch in this message | | | From | Rik van Riel <> | Subject | [PATCH 08/15] sched,fair: simplify timeslice length code | Date | Wed, 21 Aug 2019 22:17:33 -0400 |
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The idea behind __sched_period makes sense, but the results do not always.
When a CPU has one high priority task and a large number of low priority tasks, __sched_period will return a value larger than sysctl_sched_latency, and the one high priority task may end up getting a timeslice all for itself that is also much larger than sysctl_sched_latency.
The low priority tasks will have their time slices rounded up to sysctl_sched_min_granularity, resulting in an even larger scheduling latency than targeted by __sched_period.
Simplify the code by simply ripping out __sched_period and always taking fractions of sysctl_sched_latency.
If a high priority task ends up getting a "too small" time slice compared to low priority tasks, the vruntime scaling ensures that it will simply get scheduled more frequently than low priority tasks.
Signed-off-by: Rik van Riel <riel@surriel.com> --- kernel/sched/fair.c | 18 +----------------- 1 file changed, 1 insertion(+), 17 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 8f8c85c6da9b..74ee22c59d13 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -691,22 +691,6 @@ 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. @@ -715,7 +699,7 @@ 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; for_each_sched_entity(se) { struct load_weight *load; -- 2.20.1
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