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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: b7031a02ec ("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
This commit is contained in:
Vincent Guittot 2020-06-09 14:37:48 +02:00 committed by Peter Zijlstra
parent b4098bfc5e
commit 3ea2f097b1
1 changed files with 14 additions and 9 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

23
kernel/sched/fair.c
View File

@ -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 @@ 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;
}