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Date: Tue, 05 Oct 2021 14:12:17 -0000
From: "tip-bot2 for Valentin Schneider" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Vincent Guittot <vincent.guittot@...aro.org>,
Valentin Schneider <valentin.schneider@....com>,
"Peter Zijlstra (Intel)" <peterz@...radead.org>, x86@...nel.org,
linux-kernel@...r.kernel.org
Subject: [tip: sched/core] sched/fair: Add NOHZ balancer flag for
nohz.next_balance updates
The following commit has been merged into the sched/core branch of tip:
Commit-ID: efd984c481abb516fab8bafb25bf41fd9397a43c
Gitweb: https://git.kernel.org/tip/efd984c481abb516fab8bafb25bf41fd9397a43c
Author: Valentin Schneider <valentin.schneider@....com>
AuthorDate: Mon, 23 Aug 2021 12:16:59 +01:00
Committer: Peter Zijlstra <peterz@...radead.org>
CommitterDate: Tue, 05 Oct 2021 15:51:30 +02:00
sched/fair: Add NOHZ balancer flag for nohz.next_balance updates
A following patch will trigger NOHZ idle balances as a means to update
nohz.next_balance. Vincent noted that blocked load updates can have
non-negligible overhead, which should be avoided if the intent is to only
update nohz.next_balance.
Add a new NOHZ balance kick flag, NOHZ_NEXT_KICK. Gate NOHZ blocked load
update by the presence of NOHZ_STATS_KICK - currently all NOHZ balance
kicks will have the NOHZ_STATS_KICK flag set, so no change in behaviour is
expected.
Suggested-by: Vincent Guittot <vincent.guittot@...aro.org>
Signed-off-by: Valentin Schneider <valentin.schneider@....com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Reviewed-by: Vincent Guittot <vincent.guittot@...aro.org>
Link: https://lkml.kernel.org/r/20210823111700.2842997-2-valentin.schneider@arm.com
---
kernel/sched/fair.c | 24 ++++++++++++++----------
kernel/sched/sched.h | 8 +++++++-
2 files changed, 21 insertions(+), 11 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index f6a05d9..f4de7f5 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -10375,7 +10375,7 @@ static void nohz_balancer_kick(struct rq *rq)
goto out;
if (rq->nr_running >= 2) {
- flags = NOHZ_KICK_MASK;
+ flags = NOHZ_STATS_KICK | NOHZ_BALANCE_KICK;
goto out;
}
@@ -10389,7 +10389,7 @@ static void nohz_balancer_kick(struct rq *rq)
* on.
*/
if (rq->cfs.h_nr_running >= 1 && check_cpu_capacity(rq, sd)) {
- flags = NOHZ_KICK_MASK;
+ flags = NOHZ_STATS_KICK | NOHZ_BALANCE_KICK;
goto unlock;
}
}
@@ -10403,7 +10403,7 @@ static void nohz_balancer_kick(struct rq *rq)
*/
for_each_cpu_and(i, sched_domain_span(sd), nohz.idle_cpus_mask) {
if (sched_asym_prefer(i, cpu)) {
- flags = NOHZ_KICK_MASK;
+ flags = NOHZ_STATS_KICK | NOHZ_BALANCE_KICK;
goto unlock;
}
}
@@ -10416,7 +10416,7 @@ static void nohz_balancer_kick(struct rq *rq)
* to run the misfit task on.
*/
if (check_misfit_status(rq, sd)) {
- flags = NOHZ_KICK_MASK;
+ flags = NOHZ_STATS_KICK | NOHZ_BALANCE_KICK;
goto unlock;
}
@@ -10443,7 +10443,7 @@ static void nohz_balancer_kick(struct rq *rq)
*/
nr_busy = atomic_read(&sds->nr_busy_cpus);
if (nr_busy > 1) {
- flags = NOHZ_KICK_MASK;
+ flags = NOHZ_STATS_KICK | NOHZ_BALANCE_KICK;
goto unlock;
}
}
@@ -10605,7 +10605,8 @@ static void _nohz_idle_balance(struct rq *this_rq, unsigned int flags,
* setting the flag, we are sure to not clear the state and not
* check the load of an idle cpu.
*/
- WRITE_ONCE(nohz.has_blocked, 0);
+ if (flags & NOHZ_STATS_KICK)
+ WRITE_ONCE(nohz.has_blocked, 0);
/*
* Ensures that if we miss the CPU, we must see the has_blocked
@@ -10627,13 +10628,15 @@ static void _nohz_idle_balance(struct rq *this_rq, unsigned int flags,
* balancing owner will pick it up.
*/
if (need_resched()) {
- has_blocked_load = true;
+ if (flags & NOHZ_STATS_KICK)
+ has_blocked_load = true;
goto abort;
}
rq = cpu_rq(balance_cpu);
- has_blocked_load |= update_nohz_stats(rq);
+ if (flags & NOHZ_STATS_KICK)
+ has_blocked_load |= update_nohz_stats(rq);
/*
* If time for next balance is due,
@@ -10664,8 +10667,9 @@ static void _nohz_idle_balance(struct rq *this_rq, unsigned int flags,
if (likely(update_next_balance))
nohz.next_balance = next_balance;
- WRITE_ONCE(nohz.next_blocked,
- now + msecs_to_jiffies(LOAD_AVG_PERIOD));
+ if (flags & NOHZ_STATS_KICK)
+ WRITE_ONCE(nohz.next_blocked,
+ now + msecs_to_jiffies(LOAD_AVG_PERIOD));
abort:
/* There is still blocked load, enable periodic update */
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 3d3e579..1fec313 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -2709,12 +2709,18 @@ extern void cfs_bandwidth_usage_dec(void);
#define NOHZ_BALANCE_KICK_BIT 0
#define NOHZ_STATS_KICK_BIT 1
#define NOHZ_NEWILB_KICK_BIT 2
+#define NOHZ_NEXT_KICK_BIT 3
+/* Run rebalance_domains() */
#define NOHZ_BALANCE_KICK BIT(NOHZ_BALANCE_KICK_BIT)
+/* Update blocked load */
#define NOHZ_STATS_KICK BIT(NOHZ_STATS_KICK_BIT)
+/* Update blocked load when entering idle */
#define NOHZ_NEWILB_KICK BIT(NOHZ_NEWILB_KICK_BIT)
+/* Update nohz.next_balance */
+#define NOHZ_NEXT_KICK BIT(NOHZ_NEXT_KICK_BIT)
-#define NOHZ_KICK_MASK (NOHZ_BALANCE_KICK | NOHZ_STATS_KICK)
+#define NOHZ_KICK_MASK (NOHZ_BALANCE_KICK | NOHZ_STATS_KICK | NOHZ_NEXT_KICK)
#define nohz_flags(cpu) (&cpu_rq(cpu)->nohz_flags)
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