[lkml]   [2018]   [Sep]   [26]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
Patch in this message
Subject[PATCH v2 2/2] sched/fair: Don't increase sd->balance_interval on newidle balance
When load_balance() fails to move some load because of task affinity,
we end up increasing sd->balance_interval to delay the next periodic
balance in the hopes that next time we look, that annoying pinned
task(s) will be gone.

However, idle_balance() pays no attention to sd->balance_interval, yet
it will still lead to an increase in balance_interval in case of
pinned tasks.

If we're going through several newidle balances (e.g. we have a
periodic task), this can lead to a huge increase of the
balance_interval in a very small amount of time.

To prevent that, don't increase the balance interval when going
through a newidle balance.

This is a similar approach to what is done in commit 58b26c4c0257
("sched: Increment cache_nice_tries only on periodic lb"), where we
disregard newidle balance and rely on periodic balance for more stable

Signed-off-by: Valentin Schneider <>
kernel/sched/fair.c | 13 +++++++++++--
1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 9cf93ba..4c33283 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -8782,13 +8782,22 @@ static int load_balance(int this_cpu, struct rq *this_rq,
sd->nr_balance_failed = 0;

+ ld_moved = 0;
+ /*
+ * idle_balance() disregards balance intervals, so we could repeatedly
+ * reach this code, which would lead to balance_interval skyrocketting
+ * in a short amount of time. Skip the balance_interval increase logic
+ * to avoid that.
+ */
+ if (env.idle == CPU_NEWLY_IDLE)
+ goto out;
/* tune up the balancing interval */
if ((env.flags & LBF_ALL_PINNED &&
sd->balance_interval < MAX_PINNED_INTERVAL) ||
sd->balance_interval < sd->max_interval)
sd->balance_interval *= 2;
- ld_moved = 0;
return ld_moved;
 \ /
  Last update: 2018-09-26 17:14    [W:0.119 / U:0.116 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site