kernel/sched/fair.c | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-)
Active balancing needs the help by migration threads which will interrupt
task on src_rq. It has a certain impact on overall performance. Active
balancing often fails, there is a check to determine whether the current
task(say it 'curr') on src_rq can run on dst_rq. We have observed that
even that, if curr is a CFS task and on_rq is 0, the failure rate of
active balancing is very high. Below are the test data from a certain
fillback task scenario executed on a platform with 18 CPUs over 300
seconds:
total: the total count of cases that match
cpumask_test_cpu(this_cpu, busiest->curr->cpus_ptr) &&
busiest->curr->sched_class == &fair_sched_class &&
!busiest->curr->on_rq
succ: the active balance success cases that match
cpumask_......->on_rq
fail: the active balance fail cases that match
cpumask_......->on_rq
total succ fail
cpu0 domain0 00003 0 0 0
cpu0 domain1 3ffff 32 0 32
cpu1 domain0 00003 0 0 0
cpu1 domain1 3ffff 40 0 40
cpu2 domain0 0003c 3 0 3
cpu2 domain1 3ffff 6 0 6
cpu3 domain0 0003c 3 1 2
cpu3 domain1 3ffff 3 0 3
cpu4 domain0 0003c 3 0 3
cpu4 domain1 3ffff 4 0 4
cpu5 domain0 0003c 1 0 1
cpu5 domain1 3ffff 6 0 6
cpu6 domain0 003c0 39 0 39
cpu6 domain1 3ffff 36 0 36
cpu7 domain0 003c0 213 4 209
cpu7 domain1 3ffff 24 2 22
cpu8 domain0 003c0 242 16 226
cpu8 domain1 3ffff 16 0 16
cpu9 domain0 003c0 0 0 0
cpu9 domain1 3ffff 6 1 5
cpu10 domain0 03c00 58 1 57
cpu10 domain1 3ffff 0 0 0
cpu11 domain0 03c00 54 4 50
cpu11 domain1 3ffff 1 0 1
cpu12 domain0 03c00 66 1 65
cpu12 domain1 3ffff 0 0 0
cpu13 domain0 03c00 66 1 65
cpu13 domain1 3ffff 0 0 0
cpu14 domain0 3c000 0 0 0
cpu14 domain1 3ffff 57 5 52
cpu15 domain0 3c000 15 0 15
cpu15 domain1 3ffff 35 0 35
cpu16 domain0 3c000 148 3 145
cpu16 domain1 3ffff 109 1 108
cpu17 domain0 3c000 182 2 180
cpu17 domain1 3ffff 78 1 77
We add the situation not to perform active balancing. For cases where
src_rq->curr is a non-CFS task, we retain the affinity check for dst_rq
because such task is likely to wake-up or woken-by src_rq CFS task which
has similar affinity characteristics to migrate. We attempted to execute
list_move_tail for the curr CFS task on src_rq before unlocking src_rq,
but testing showed no improvement in the traversal count of cfs_tasks in
detach_one_task().
Additionally, in sched_balance_rq(), we unconditionally reset the
balance_interval to min_interval. The difference is that original logic
does not reset the balance_interval when dst_cpu softirq handler is
preempted while src_cpu successfully run the just-dispatched active
balancing, during the gaps between two need_active_balance() checks. It
seems that we haven't observed any substantial benefits from reducing the
opportunities for balance under such fluctuating conditions.
Signed-off-by: Xin Zhao <jackzxcui1989@163.com>
---
kernel/sched/fair.c | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index b5819c489..cba6dc6da 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -13423,7 +13423,9 @@ static int sched_balance_rq(int this_cpu, struct rq *this_rq,
* if the curr task on busiest CPU can't be
* moved to this_cpu:
*/
- if (!cpumask_test_cpu(this_cpu, busiest->curr->cpus_ptr)) {
+ if (!cpumask_test_cpu(this_cpu, busiest->curr->cpus_ptr) ||
+ (busiest->curr->sched_class == &fair_sched_class &&
+ !busiest->curr->on_rq)) {
raw_spin_rq_unlock_irqrestore(busiest, flags);
goto out_one_pinned;
}
@@ -13455,10 +13457,8 @@ static int sched_balance_rq(int this_cpu, struct rq *this_rq,
sd->nr_balance_failed = 0;
}
- if (likely(!active_balance) || need_active_balance(&env)) {
- /* We were unbalanced, so reset the balancing interval */
- sd->balance_interval = sd->min_interval;
- }
+ /* We were unbalanced, so reset the balancing interval */
+ sd->balance_interval = sd->min_interval;
goto out;
--
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