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sched/fair: Trigger the update of blocked load on newly idle cpu

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Instead of waking up a random and already idle CPU, we can take advantage
of this_cpu being about to enter idle to run the ILB and update the
blocked load.

Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>
Link: https://lkml.kernel.org/r/20210224133007.28644-7-vincent.guittot@linaro.org
This commit is contained in:
Vincent Guittot 2021-02-24 14:30:06 +01:00 committed by Ingo Molnar
parent 6553fc1817
commit c6f886546c
4 changed files with 35 additions and 4 deletions
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2
kernel/sched/core.c
View File

@ -737,7 +737,7 @@ static void nohz_csd_func(void *info)
/*
* Release the rq::nohz_csd.
*/
flags = atomic_fetch_andnot(NOHZ_KICK_MASK, nohz_flags(cpu));
flags = atomic_fetch_andnot(NOHZ_KICK_MASK | NOHZ_NEWILB_KICK, nohz_flags(cpu));
WARN_ON(!(flags & NOHZ_KICK_MASK));
rq->idle_balance = idle_cpu(cpu);

24
kernel/sched/fair.c
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@ -10453,6 +10453,24 @@ static bool nohz_idle_balance(struct rq *this_rq, enum cpu_idle_type idle)
return true;
}
/*
* Check if we need to run the ILB for updating blocked load before entering
* idle state.
*/
void nohz_run_idle_balance(int cpu)
{
unsigned int flags;
flags = atomic_fetch_andnot(NOHZ_NEWILB_KICK, nohz_flags(cpu));
/*
* Update the blocked load only if no SCHED_SOFTIRQ is about to happen
* (ie NOHZ_STATS_KICK set) and will do the same.
*/
if ((flags == NOHZ_NEWILB_KICK) && !need_resched())
_nohz_idle_balance(cpu_rq(cpu), NOHZ_STATS_KICK, CPU_IDLE);
}
static void nohz_newidle_balance(struct rq *this_rq)
{
int this_cpu = this_rq->cpu;
@ -10474,10 +10492,10 @@ static void nohz_newidle_balance(struct rq *this_rq)
return;
/*
* Blocked load of idle CPUs need to be updated.
* Kick an ILB to update statistics.
* Set the need to trigger ILB in order to update blocked load
* before entering idle state.
*/
kick_ilb(NOHZ_STATS_KICK);
atomic_or(NOHZ_NEWILB_KICK, nohz_flags(this_cpu));
}
#else /* !CONFIG_NO_HZ_COMMON */

6
kernel/sched/idle.c
View File

@ -261,6 +261,12 @@ exit_idle:
static void do_idle(void)
{
int cpu = smp_processor_id();
/*
* Check if we need to update blocked load
*/
nohz_run_idle_balance(cpu);
/*
* If the arch has a polling bit, we maintain an invariant:
*

7
kernel/sched/sched.h
View File

@ -2385,9 +2385,11 @@ extern void cfs_bandwidth_usage_dec(void);
#ifdef CONFIG_NO_HZ_COMMON
#define NOHZ_BALANCE_KICK_BIT 0
#define NOHZ_STATS_KICK_BIT 1
#define NOHZ_NEWILB_KICK_BIT 2
#define NOHZ_BALANCE_KICK BIT(NOHZ_BALANCE_KICK_BIT)
#define NOHZ_STATS_KICK BIT(NOHZ_STATS_KICK_BIT)
#define NOHZ_NEWILB_KICK BIT(NOHZ_NEWILB_KICK_BIT)
#define NOHZ_KICK_MASK (NOHZ_BALANCE_KICK | NOHZ_STATS_KICK)
@ -2398,6 +2400,11 @@ extern void nohz_balance_exit_idle(struct rq *rq);
static inline void nohz_balance_exit_idle(struct rq *rq) { }
#endif
#if defined(CONFIG_SMP) && defined(CONFIG_NO_HZ_COMMON)
extern void nohz_run_idle_balance(int cpu);
#else
static inline void nohz_run_idle_balance(int cpu) { }
#endif
#ifdef CONFIG_SMP
static inline