On Fri, Aug 25, 2017 at 12:11:31AM +0200, Uladzislau Rezki (Sony) wrote: > From: Uladzislau Rezki <ure...@gmail.com> > > As a first step this patch makes cfs_tasks list as MRU one. > It means, that when a next task is picked to run on physical > CPU it is moved to the front of the list. > > Thefore, the cfs_tasks list is more or less sorted (except woken > tasks) starting from recently given CPU time tasks toward tasks > with max wait time in a run-queue, i.e. MRU list. > > Second, as part of the load balance operation, this approach > starts detach_tasks()/detach_one_task() from the tail of the > queue instead of the head, giving some advantages: > > - tends to pick a task with highest wait time; > - tasks located in the tail are less likely cache-hot, > therefore the can_migrate_task() decision is higher. > > hackbench illustrates slightly better performance. For example > doing 1000 samples and 40 groups on i5-3320M CPU, it shows below > figures: > > default: 0.644 avg > patched: 0.637 avg > > Signed-off-by: Uladzislau Rezki (Sony) <ure...@gmail.com> > --- > kernel/sched/fair.c | 19 ++++++++++++++----- > 1 file changed, 14 insertions(+), 5 deletions(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index c77e4b1d51c0..cda281c6bb29 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -6357,7 +6357,7 @@ pick_next_task_fair(struct rq *rq, struct task_struct > *prev, struct rq_flags *rf > if (hrtick_enabled(rq)) > hrtick_start_fair(rq, p); > > - return p; > + goto done; > simple: > cfs_rq = &rq->cfs; > #endif > @@ -6378,6 +6378,14 @@ pick_next_task_fair(struct rq *rq, struct task_struct > *prev, struct rq_flags *rf > if (hrtick_enabled(rq)) > hrtick_start_fair(rq, p); > > +done: __maybe_unused > + /* > + * Move the next running task to the front of > + * the list, so our cfs_tasks list becomes MRU > + * one. > + */ > + list_move(&se->group_node, &rq->cfs_tasks); > + > return p; > > idle:
Could you also run something like: $ taskset 1 perf bench sched pipe to make sure the added list_move() doesn't hurt, I'm not sure group_node and cfs_tasks are in cachelines we already touch for that operation. And if you can see that list_move() hurt in "perf annotate", try moving those members around to lines that we already need anyway.
