Commit 3ea2f097 authored by Vincent Guittot's avatar Vincent Guittot Committed by Peter Zijlstra

sched/fair: Fix NOHZ next idle balance

With commit:
  'b7031a02 ("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: b7031a02 ("sched/fair: Add NOHZ_STATS_KICK")
Reported-by: default avatarPeng Liu <iwtbavbm@gmail.com>
Signed-off-by: default avatarVincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: default avatarValentin Schneider <valentin.schneider@arm.com>
Acked-by: default avatarMel Gorman <mgorman@suse.de>
Link: https://lkml.kernel.org/r/20200609123748.18636-1-vincent.guittot@linaro.org
parent b4098bfc
...@@ -10022,7 +10022,12 @@ static void kick_ilb(unsigned int flags) ...@@ -10022,7 +10022,12 @@ static void kick_ilb(unsigned int flags)
{ {
int ilb_cpu; 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(); ilb_cpu = find_new_ilb();
...@@ -10343,6 +10348,14 @@ static bool _nohz_idle_balance(struct rq *this_rq, unsigned int flags, ...@@ -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 */ /* Newly idle CPU doesn't need an update */
if (idle != CPU_NEWLY_IDLE) { if (idle != CPU_NEWLY_IDLE) {
update_blocked_averages(this_cpu); update_blocked_averages(this_cpu);
...@@ -10363,14 +10376,6 @@ static bool _nohz_idle_balance(struct rq *this_rq, unsigned int flags, ...@@ -10363,14 +10376,6 @@ static bool _nohz_idle_balance(struct rq *this_rq, unsigned int flags,
if (has_blocked_load) if (has_blocked_load)
WRITE_ONCE(nohz.has_blocked, 1); 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; return ret;
} }
......
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