Messages in this thread Patch in this message | | | From | Valentin Schneider <> | Subject | [PATCH v2 2/7] sched/fair: Clean up active balance nr_balance_failed trickery | Date | Fri, 19 Feb 2021 12:59:58 +0000 |
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When triggering an active load balance, sd->nr_balance_failed is set to such a value that any further can_migrate_task() using said sd will ignore the output of task_hot().
This behaviour makes sense, as active load balance intentionally preempts a rq's running task to migrate it right away, but this asynchronous write is a bit shoddy, as the stopper thread might run active_load_balance_cpu_stop before the sd->nr_balance_failed write either becomes visible to the stopper's CPU or even happens on the CPU that appended the stopper work.
Add a struct lb_env flag to denote active balancing, and use it in can_migrate_task(). Remove the sd->nr_balance_failed write that served the same purpose.
Signed-off-by: Valentin Schneider <valentin.schneider@arm.com> --- kernel/sched/fair.c | 17 ++++++++++------- 1 file changed, 10 insertions(+), 7 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 2d4dcf1a3372..535ebc31c9a8 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -7394,6 +7394,7 @@ enum migration_type { #define LBF_SOME_PINNED 0x08 #define LBF_NOHZ_STATS 0x10 #define LBF_NOHZ_AGAIN 0x20 +#define LBF_ACTIVE_LB 0x40 struct lb_env { struct sched_domain *sd; @@ -7583,10 +7584,14 @@ int can_migrate_task(struct task_struct *p, struct lb_env *env) /* * Aggressive migration if: - * 1) destination numa is preferred - * 2) task is cache cold, or - * 3) too many balance attempts have failed. + * 1) active balance + * 2) destination numa is preferred + * 3) task is cache cold, or + * 4) too many balance attempts have failed. */ + if (env->flags & LBF_ACTIVE_LB) + return 1; + tsk_cache_hot = migrate_degrades_locality(p, env); if (tsk_cache_hot == -1) tsk_cache_hot = task_hot(p, env); @@ -9780,9 +9785,6 @@ static int load_balance(int this_cpu, struct rq *this_rq, active_load_balance_cpu_stop, busiest, &busiest->active_balance_work); } - - /* We've kicked active balancing, force task migration. */ - sd->nr_balance_failed = sd->cache_nice_tries+1; } } else { sd->nr_balance_failed = 0; @@ -9938,7 +9940,8 @@ static int active_load_balance_cpu_stop(void *data) * @dst_grpmask we need to make that test go away with lying * about DST_PINNED. */ - .flags = LBF_DST_PINNED, + .flags = LBF_DST_PINNED | + LBF_ACTIVE_LB, }; schedstat_inc(sd->alb_count); -- 2.27.0
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