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Date: Thu, 21 Dec 2017 17:23:27 +0100
From: Vincent Guittot <vincent.guittot@...aro.org>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Ingo Molnar <mingo@...nel.org>,
linux-kernel <linux-kernel@...r.kernel.org>,
Brendan Jackman <brendan.jackman@....com>,
Dietmar Eggemann <dietmar.eggemann@....com>,
Morten Rasmussen <morten.rasmussen@....com>
Subject: Re: [RFC PATCH 2/5] sched: Add NOHZ_STATS_KICK
Hi Peter,
I think that part of the proposal is missing.
One goal of the patchset was to kick an update of the stats of idle
cpu when a task wake up on a cpu but the statistic has not been
updated for a while.
That's why there where a call to nohz_kick_needed in the proposal to
kick ilb but only for updating blocked load and not a full idle load
balance
I can't find this call any more in your patchset
On 21 December 2017 at 11:21, Peter Zijlstra <peterz@...radead.org> wrote:
>
> Suggested-by: Vincent Guittot <vincent.guittot@...aro.org>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> ---
> kernel/sched/core.c | 4 +--
> kernel/sched/fair.c | 52 ++++++++++++++++++++++++++++++++++-----------------
> kernel/sched/sched.h | 4 +++
> 3 files changed, 41 insertions(+), 19 deletions(-)
>
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -608,7 +608,7 @@ static inline bool got_nohz_idle_kick(vo
> {
> int cpu = smp_processor_id();
>
> - if (!(atomic_read(nohz_flags(cpu)) & NOHZ_BALANCE_KICK))
> + if (!(atomic_read(nohz_flags(cpu)) & NOHZ_KICK_MASK))
> return false;
>
> if (idle_cpu(cpu) && !need_resched())
> @@ -618,7 +618,7 @@ static inline bool got_nohz_idle_kick(vo
> * We can't run Idle Load Balance on this CPU for this time so we
> * cancel it and clear NOHZ_BALANCE_KICK
> */
> - atomic_andnot(NOHZ_BALANCE_KICK, nohz_flags(cpu));
> + atomic_andnot(NOHZ_KICK_MASK, nohz_flags(cpu));
> return false;
> }
>
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -9001,8 +9001,8 @@ static void nohz_balancer_kick(void)
> if (ilb_cpu >= nr_cpu_ids)
> return;
>
> - flags = atomic_fetch_or(NOHZ_BALANCE_KICK, nohz_flags(ilb_cpu));
> - if (flags & NOHZ_BALANCE_KICK)
> + flags = atomic_fetch_or(NOHZ_KICK_MASK, nohz_flags(ilb_cpu));
> + if (flags & NOHZ_KICK_MASK)
> return;
> /*
> * Use smp_send_reschedule() instead of resched_cpu().
> @@ -9125,8 +9125,6 @@ static void rebalance_domains(struct rq
> int need_serialize, need_decay = 0;
> u64 max_cost = 0;
>
> - update_blocked_averages(cpu);
> -
> rcu_read_lock();
> for_each_domain(cpu, sd) {
> /*
> @@ -9221,20 +9219,27 @@ static void rebalance_domains(struct rq
> * In CONFIG_NO_HZ_COMMON case, the idle balance kickee will do the
> * rebalancing for all the cpus for whom scheduler ticks are stopped.
> */
> -static void nohz_idle_balance(struct rq *this_rq, enum cpu_idle_type idle)
> +static bool nohz_idle_balance(struct rq *this_rq, enum cpu_idle_type idle)
> {
> - int this_cpu = this_rq->cpu;
> - struct rq *rq;
> - int balance_cpu;
> /* Earliest time when we have to do rebalance again */
> unsigned long next_balance = jiffies + 60*HZ;
> int update_next_balance = 0;
> + int this_cpu = this_rq->cpu;
> + unsigned int flags;
> + int balance_cpu;
> + struct rq *rq;
>
> - if (!(atomic_read(nohz_flags(this_cpu)) & NOHZ_BALANCE_KICK))
> - return;
> + if (!(atomic_read(nohz_flags(this_cpu)) & NOHZ_KICK_MASK))
> + return false;
>
> - if (idle != CPU_IDLE)
> - goto end;
> + if (idle != CPU_IDLE) {
> + atomic_andnot(NOHZ_KICK_MASK, nohz_flags(this_cpu));
> + return false;
> + }
> +
> + flags = atomic_fetch_andnot(NOHZ_KICK_MASK, nohz_flags(this_cpu));
> +
> + SCHED_WARN_ON((flags & NOHZ_KICK_MASK) == NOHZ_BALANCE_KICK);
>
> for_each_cpu(balance_cpu, nohz.idle_cpus_mask) {
> if (balance_cpu == this_cpu || !idle_cpu(balance_cpu))
> @@ -9262,7 +9267,9 @@ static void nohz_idle_balance(struct rq
> cpu_load_update_idle(rq);
> rq_unlock_irq(rq, &rf);
>
> - rebalance_domains(rq, CPU_IDLE);
> + update_blocked_averages(rq->cpu);
> + if (flags & NOHZ_BALANCE_KICK)
> + rebalance_domains(rq, CPU_IDLE);
> }
>
> if (time_after(next_balance, rq->next_balance)) {
> @@ -9271,6 +9278,10 @@ static void nohz_idle_balance(struct rq
> }
> }
>
> + update_blocked_averages(this_cpu);
> + if (flags & NOHZ_BALANCE_KICK)
> + rebalance_domains(this_rq, CPU_IDLE);
> +
> /*
> * 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
> @@ -9278,8 +9289,8 @@ static void nohz_idle_balance(struct rq
> */
> if (likely(update_next_balance))
> nohz.next_balance = next_balance;
> -end:
> - atomic_andnot(NOHZ_BALANCE_KICK, nohz_flags(this_cpu));
> +
> + return true;
> }
>
> /*
> @@ -9366,7 +9377,10 @@ static inline bool nohz_kick_needed(stru
> return kick;
> }
> #else
> -static void nohz_idle_balance(struct rq *this_rq, enum cpu_idle_type idle) { }
> +static bool nohz_idle_balance(struct rq *this_rq, enum cpu_idle_type idle)
> +{
> + return false;
> +}
> #endif
>
> /*
> @@ -9387,7 +9401,11 @@ static __latent_entropy void run_rebalan
> * load balance only within the local sched_domain hierarchy
> * and abort nohz_idle_balance altogether if we pull some load.
> */
> - nohz_idle_balance(this_rq, idle);
> + if (nohz_idle_balance(this_rq, idle))
> + return;
> +
> + /* normal load balance */
> + update_blocked_averages(this_rq->cpu);
> rebalance_domains(this_rq, idle);
> }
>
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -2005,9 +2005,13 @@ extern void cfs_bandwidth_usage_dec(void
> #ifdef CONFIG_NO_HZ_COMMON
> #define NOHZ_TICK_STOPPED_BIT 0
> #define NOHZ_BALANCE_KICK_BIT 1
> +#define NOHZ_STATS_KICK_BIT 2
>
> #define NOHZ_TICK_STOPPED BIT(NOHZ_TICK_STOPPED_BIT)
> #define NOHZ_BALANCE_KICK BIT(NOHZ_BALANCE_KICK_BIT)
> +#define NOHZ_STATS_KICK BIT(NOHZ_STATS_KICK_BIT)
> +
> +#define NOHZ_KICK_MASK (NOHZ_BALANCE_KICK | NOHZ_STATS_KICK)
>
> #define nohz_flags(cpu) (&cpu_rq(cpu)->nohz_flags)
>
>
>
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