Messages in this thread Patch in this message | | | From | Valentin Schneider <> | Subject | [PATCH v2 1/2] sched/fair: Add NOHZ balancer flag for nohz.next_balance updates | Date | Mon, 19 Jul 2021 11:31:16 +0100 |
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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@linaro.org> Signed-off-by: Valentin Schneider <valentin.schneider@arm.com> --- kernel/sched/fair.c | 9 ++++++--- kernel/sched/sched.h | 8 +++++++- 2 files changed, 13 insertions(+), 4 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 11d22943753f..5c88698c3664 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -10506,7 +10506,8 @@ 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 @@ -10528,13 +10529,15 @@ 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, diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index 9a1c6aeb9165..b0f38b5d2550 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -2695,12 +2695,18 @@ 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) -- 2.25.1
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