Messages in this thread Patch in this message | | | Date | Tue, 16 Jun 2020 12:21:53 -0000 | From | "tip-bot2 for Vincent Guittot" <> | Subject | [tip: sched/core] sched/fair: Fix NOHZ next idle balance |
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The following commit has been merged into the sched/core branch of tip:
Commit-ID: 3ea2f097b17e13a8280f1f9386c331b326a3dbef Gitweb: https://git.kernel.org/tip/3ea2f097b17e13a8280f1f9386c331b326a3dbef Author: Vincent Guittot <vincent.guittot@linaro.org> AuthorDate: Tue, 09 Jun 2020 14:37:48 +02:00 Committer: Peter Zijlstra <peterz@infradead.org> CommitterDate: Mon, 15 Jun 2020 14:10:04 +02:00
sched/fair: Fix NOHZ next idle balance
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 --- 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 a785a9b..295c9ff 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -10022,7 +10022,12 @@ 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(); @@ -10343,6 +10348,14 @@ 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); @@ -10363,14 +10376,6 @@ abort: 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; }
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