From: Vincent Guittot vincent.guittot@linaro.org
[ Upstream commit 3ea2f097b17e13a8280f1f9386c331b326a3dbef ]
With commit: 'b7031a02ec75 ("sched/fair: Add NOHZ_STATS_KICK")' rebalance_domains of the local cfs_rq happens before others idle cpus have updated nohz.next_balance and its value is overwritten.
Move the update of nohz.next_balance for other idles cpus before balancing and updating the next_balance of local cfs_rq.
Also, the nohz.next_balance is now updated only if all idle cpus got a chance to rebalance their domains and the idle balance has not been aborted because of new activities on the CPU. In case of need_resched, the idle load balance will be kick the next jiffie in order to address remaining ilb.
Fixes: b7031a02ec75 ("sched/fair: Add NOHZ_STATS_KICK") Reported-by: Peng Liu iwtbavbm@gmail.com Signed-off-by: Vincent Guittot vincent.guittot@linaro.org Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Reviewed-by: Valentin Schneider valentin.schneider@arm.com Acked-by: Mel Gorman mgorman@suse.de Link: https://lkml.kernel.org/r/20200609123748.18636-1-vincent.guittot@linaro.org Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/sched/fair.c | 23 ++++++++++++++--------- 1 file changed, 14 insertions(+), 9 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 04fa8dbcfa4d7..6b3b59cc51d6c 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -10027,7 +10027,12 @@ static void kick_ilb(unsigned int flags) { int ilb_cpu;
- nohz.next_balance++; + /* + * Increase nohz.next_balance only when if full ilb is triggered but + * not if we only update stats. + */ + if (flags & NOHZ_BALANCE_KICK) + nohz.next_balance = jiffies+1;
ilb_cpu = find_new_ilb();
@@ -10348,6 +10353,14 @@ static bool _nohz_idle_balance(struct rq *this_rq, unsigned int flags, } }
+ /* + * next_balance will be updated only when there is a need. + * When the CPU is attached to null domain for ex, it will not be + * updated. + */ + if (likely(update_next_balance)) + nohz.next_balance = next_balance; + /* Newly idle CPU doesn't need an update */ if (idle != CPU_NEWLY_IDLE) { update_blocked_averages(this_cpu); @@ -10368,14 +10381,6 @@ static bool _nohz_idle_balance(struct rq *this_rq, unsigned int flags, if (has_blocked_load) WRITE_ONCE(nohz.has_blocked, 1);
- /* - * next_balance will be updated only when there is a need. - * When the CPU is attached to null domain for ex, it will not be - * updated. - */ - if (likely(update_next_balance)) - nohz.next_balance = next_balance; - return ret; }