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Date: Sun, 3 May 2020 16:34:07 +0800 From: Peng Liu <iwtbavbm@...il.com> To: linux-kernel@...r.kernel.org Cc: mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com, vincent.guittot@...aro.org, dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de, valentin.schneider@....com, iwtbavbm@...il.com Subject: [PATCH] sched/fair: Fix nohz.next_balance update commit c5afb6a87f23 ("sched/fair: Fix nohz.next_balance update") During idle load balance, this_cpu(ilb) do load balance for the other idle CPUs, also gather the earliest (nohz.)next_balance. Since commit: 'b7031a02ec75 ("sched/fair: Add NOHZ_STATS_KICK")' We update nohz.next_balance like this: _nohz_idle_balance() { for_each_cpu(nohz.idle_cpus_mask) { rebalance_domains() { update nohz.next_balance <-- compare and update } } rebalance_domains(this_cpu) { update nohz.next_balance <-- compare and update } update nohz.next_balance <-- unconditionally update } For instance, nohz.idle_cpus_mask spans {cpu2,3,5,8}, and this_cpu is cpu5. After the above loop we could gather the earliest *next_balance* among {cpu2,3,8}, then rebalance_domains(this_cpu) update nohz.next_balance with this_rq->next_balance, but finally overwrite nohz.next_balance with the earliest *next_balance* among {cpu2,3,8}, we may end up with not getting the earliest next_balance. Since we can gather all the updated rq->next_balance, including this_cpu, in _nohz_idle_balance(), it's safe to remove the extra lines in rebalance_domains() which are originally intended for this_cpu. And finally the updating only happen in _nohz_idle_balance(). Signed-off-by: Peng Liu <iwtbavbm@...il.com> Cc: Ingo Molnar <mingo@...hat.com> Cc: Peter Zijlstra <peterz@...radead.org> Cc: Juri Lelli <juri.lelli@...hat.com> Cc: Vincent Guittot <vincent.guittot@...aro.org> Cc: Dietmar Eggemann <dietmar.eggemann@....com> Cc: Steven Rostedt <rostedt@...dmis.org> Cc: Ben Segall <bsegall@...gle.com> Cc: Mel Gorman <mgorman@...e.de> Cc: Valentin Schneider <valentin.schneider@....com> --- kernel/sched/fair.c | 24 ++++++++---------------- 1 file changed, 8 insertions(+), 16 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 02f323b85b6d..1d0cf33fefad 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -9943,22 +9943,8 @@ static void rebalance_domains(struct rq *rq, enum cpu_idle_type idle) * When the cpu is attached to null domain for ex, it will not be * updated. */ - if (likely(update_next_balance)) { + if (likely(update_next_balance)) rq->next_balance = next_balance; - -#ifdef CONFIG_NO_HZ_COMMON - /* - * If this CPU has been elected to perform the nohz idle - * balance. Other idle CPUs have already rebalanced with - * nohz_idle_balance() and nohz.next_balance has been - * updated accordingly. This CPU is now running the idle load - * balance for itself and we need to update the - * nohz.next_balance accordingly. - */ - if ((idle == CPU_IDLE) && time_after(nohz.next_balance, rq->next_balance)) - nohz.next_balance = rq->next_balance; -#endif - } } static inline int on_null_domain(struct rq *rq) @@ -10321,9 +10307,15 @@ static bool _nohz_idle_balance(struct rq *this_rq, unsigned int flags, has_blocked_load |= this_rq->has_blocked_load; } - if (flags & NOHZ_BALANCE_KICK) + if (flags & NOHZ_BALANCE_KICK) { rebalance_domains(this_rq, CPU_IDLE); + if (time_after(next_balance, this_rq->next_balance)) { + next_balance = this_rq->next_balance; + update_next_balance = 1; + } + } + WRITE_ONCE(nohz.next_blocked, now + msecs_to_jiffies(LOAD_AVG_PERIOD)); -- 2.17.1
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