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Date: Mon, 26 Aug 2019 09:51:47 -0700
From: mark gross <mgross@...ux.intel.com>
To: Vineeth Remanan Pillai <vpillai@...italocean.com>
Cc: Nishanth Aravamudan <naravamudan@...italocean.com>,
Julien Desfossez <jdesfossez@...italocean.com>,
Peter Zijlstra <peterz@...radead.org>,
Tim Chen <tim.c.chen@...ux.intel.com>, mingo@...nel.org,
tglx@...utronix.de, pjt@...gle.com, torvalds@...ux-foundation.org,
linux-kernel@...r.kernel.org, subhra.mazumdar@...cle.com,
fweisbec@...il.com, keescook@...omium.org, kerrnel@...gle.com,
Phil Auld <pauld@...hat.com>, Aaron Lu <aaron.lwe@...il.com>,
Aubrey Li <aubrey.intel@...il.com>,
Valentin Schneider <valentin.schneider@....com>,
Mel Gorman <mgorman@...hsingularity.net>,
Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [RFC PATCH v3 07/16] sched: Allow put_prev_task() to drop
rq->lock
On Wed, May 29, 2019 at 08:36:43PM +0000, Vineeth Remanan Pillai wrote:
> From: Peter Zijlstra <peterz@...radead.org>
>
> Currently the pick_next_task() loop is convoluted and ugly because of
> how it can drop the rq->lock and needs to restart the picking.
>
> For the RT/Deadline classes, it is put_prev_task() where we do
> balancing, and we could do this before the picking loop. Make this
> possible.
Maybe explain why adding strtu rq_flags pointers to the function call supports
the above commit coment.
--mark
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> ---
> kernel/sched/core.c | 2 +-
> kernel/sched/deadline.c | 14 +++++++++++++-
> kernel/sched/fair.c | 2 +-
> kernel/sched/idle.c | 2 +-
> kernel/sched/rt.c | 14 +++++++++++++-
> kernel/sched/sched.h | 4 ++--
> kernel/sched/stop_task.c | 2 +-
> 7 files changed, 32 insertions(+), 8 deletions(-)
>
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 32ea79fb8d29..9dfa0c53deb3 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -5595,7 +5595,7 @@ static void calc_load_migrate(struct rq *rq)
> atomic_long_add(delta, &calc_load_tasks);
> }
>
> -static void put_prev_task_fake(struct rq *rq, struct task_struct *prev)
> +static void put_prev_task_fake(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
> {
> }
>
> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> index c02b3229e2c3..45425f971eec 100644
> --- a/kernel/sched/deadline.c
> +++ b/kernel/sched/deadline.c
> @@ -1772,13 +1772,25 @@ pick_next_task_dl(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
> return p;
> }
>
> -static void put_prev_task_dl(struct rq *rq, struct task_struct *p)
> +static void put_prev_task_dl(struct rq *rq, struct task_struct *p, struct rq_flags *rf)
> {
> update_curr_dl(rq);
>
> update_dl_rq_load_avg(rq_clock_pelt(rq), rq, 1);
> if (on_dl_rq(&p->dl) && p->nr_cpus_allowed > 1)
> enqueue_pushable_dl_task(rq, p);
> +
> + if (rf && !on_dl_rq(&p->dl) && need_pull_dl_task(rq, p)) {
> + /*
> + * This is OK, because current is on_cpu, which avoids it being
> + * picked for load-balance and preemption/IRQs are still
> + * disabled avoiding further scheduler activity on it and we've
> + * not yet started the picking loop.
> + */
> + rq_unpin_lock(rq, rf);
> + pull_dl_task(rq);
> + rq_repin_lock(rq, rf);
> + }
> }
>
> /*
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 49707b4797de..8e3eb243fd9f 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -7110,7 +7110,7 @@ done: __maybe_unused;
> /*
> * Account for a descheduled task:
> */
> -static void put_prev_task_fair(struct rq *rq, struct task_struct *prev)
> +static void put_prev_task_fair(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
> {
> struct sched_entity *se = &prev->se;
> struct cfs_rq *cfs_rq;
> diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
> index dd64be34881d..1b65a4c3683e 100644
> --- a/kernel/sched/idle.c
> +++ b/kernel/sched/idle.c
> @@ -373,7 +373,7 @@ static void check_preempt_curr_idle(struct rq *rq, struct task_struct *p, int fl
> resched_curr(rq);
> }
>
> -static void put_prev_task_idle(struct rq *rq, struct task_struct *prev)
> +static void put_prev_task_idle(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
> {
> }
>
> diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
> index adec98a94f2b..51ee87c5a28a 100644
> --- a/kernel/sched/rt.c
> +++ b/kernel/sched/rt.c
> @@ -1593,7 +1593,7 @@ pick_next_task_rt(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
> return p;
> }
>
> -static void put_prev_task_rt(struct rq *rq, struct task_struct *p)
> +static void put_prev_task_rt(struct rq *rq, struct task_struct *p, struct rq_flags *rf)
> {
> update_curr_rt(rq);
>
> @@ -1605,6 +1605,18 @@ static void put_prev_task_rt(struct rq *rq, struct task_struct *p)
> */
> if (on_rt_rq(&p->rt) && p->nr_cpus_allowed > 1)
> enqueue_pushable_task(rq, p);
> +
> + if (rf && !on_rt_rq(&p->rt) && need_pull_rt_task(rq, p)) {
> + /*
> + * This is OK, because current is on_cpu, which avoids it being
> + * picked for load-balance and preemption/IRQs are still
> + * disabled avoiding further scheduler activity on it and we've
> + * not yet started the picking loop.
> + */
> + rq_unpin_lock(rq, rf);
> + pull_rt_task(rq);
> + rq_repin_lock(rq, rf);
> + }
> }
>
> #ifdef CONFIG_SMP
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index bfcbcbb25646..4cbe2bef92e4 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -1675,7 +1675,7 @@ struct sched_class {
> struct task_struct * (*pick_next_task)(struct rq *rq,
> struct task_struct *prev,
> struct rq_flags *rf);
> - void (*put_prev_task)(struct rq *rq, struct task_struct *p);
> + void (*put_prev_task)(struct rq *rq, struct task_struct *p, struct rq_flags *rf);
> void (*set_next_task)(struct rq *rq, struct task_struct *p);
>
> #ifdef CONFIG_SMP
> @@ -1721,7 +1721,7 @@ struct sched_class {
> static inline void put_prev_task(struct rq *rq, struct task_struct *prev)
> {
> WARN_ON_ONCE(rq->curr != prev);
> - prev->sched_class->put_prev_task(rq, prev);
> + prev->sched_class->put_prev_task(rq, prev, NULL);
> }
>
> static inline void set_next_task(struct rq *rq, struct task_struct *next)
> diff --git a/kernel/sched/stop_task.c b/kernel/sched/stop_task.c
> index 47a3d2a18a9a..8f414018d5e0 100644
> --- a/kernel/sched/stop_task.c
> +++ b/kernel/sched/stop_task.c
> @@ -59,7 +59,7 @@ static void yield_task_stop(struct rq *rq)
> BUG(); /* the stop task should never yield, its pointless. */
> }
>
> -static void put_prev_task_stop(struct rq *rq, struct task_struct *prev)
> +static void put_prev_task_stop(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
> {
> struct task_struct *curr = rq->curr;
> u64 delta_exec;
> --
> 2.17.1
>
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