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Date: Mon, 20 Mar 2023 16:55:23 +0800
From: Hao Jia <jiahao.os@...edance.com>
To: mingo@...hat.com, peterz@...radead.org, mingo@...nel.org,
juri.lelli@...hat.com, vincent.guittot@...aro.org,
dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
mgorman@...e.de, bristot@...hat.com, vschneid@...hat.com,
mgorman@...hsingularity.net
Cc: linux-kernel@...r.kernel.org, Josh Don <joshdon@...gle.com>,
joel@...lfernandes.org
Subject: Re: [PATCH] sched/core: Minor optimize pick_next_task() when
core-sched enable
kindly ping...
On 2023/3/8 Hao Jia wrote:
> If core-sched is enabled, sometimes we will traverse each CPU on the core
> to find the highest priority task 'max' on the entire core, and then try
> and find a runnable task that matches @max.
> But in the following case, we choose the runnable task is not the best.
>
> core max: task2 (cookie 0)
>
> rq0 rq1
> task0(cookie non-zero) task2(cookie 0)
> task1(cookie 0)
> task3(cookie 0)
> ...
>
> pick-task: idle pick-task: task2
>
> CPU0 and CPU1 are two CPUs on the same core, task0 and task2 are the
> highest priority tasks on rq0 and rq1 respectively, task2 is @max
> on the entire core.
>
> In the case that 'max' has a zero cookie, instead of continuing to
> search for a runnable task on rq0 that matches @max's cookie, we
> choose idle for rq0 directly.
> At this time, it is obviously better to choose task1 to run for rq0,
> which will increase the CPU utilization.
> Therefore, we queue tasks with zero cookies in core_tree, and record
> the number of non-zero cookie tasks of each rq to detect the status
> of the sched-core.
>
> Signed-off-by: Hao Jia <jiahao.os@...edance.com>
> ---
> kernel/sched/core.c | 29 +++++++++++++++--------------
> kernel/sched/core_sched.c | 9 ++++-----
> kernel/sched/sched.h | 1 +
> 3 files changed, 20 insertions(+), 19 deletions(-)
>
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index af017e038b48..765cd14c52e1 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -236,8 +236,8 @@ void sched_core_enqueue(struct rq *rq, struct task_struct *p)
> {
> rq->core->core_task_seq++;
>
> - if (!p->core_cookie)
> - return;
> + if (p->core_cookie)
> + rq->cookied_count++;
>
> rb_add(&p->core_node, &rq->core_tree, rb_sched_core_less);
> }
> @@ -246,11 +246,16 @@ void sched_core_dequeue(struct rq *rq, struct task_struct *p, int flags)
> {
> rq->core->core_task_seq++;
>
> + if (p->core_cookie)
> + rq->cookied_count--;
> +
> if (sched_core_enqueued(p)) {
> rb_erase(&p->core_node, &rq->core_tree);
> RB_CLEAR_NODE(&p->core_node);
> }
>
> + if (!sched_core_enabled(rq))
> + return;
> /*
> * Migrating the last task off the cpu, with the cpu in forced idle
> * state. Reschedule to create an accounting edge for forced idle,
> @@ -370,7 +375,7 @@ static void sched_core_assert_empty(void)
> int cpu;
>
> for_each_possible_cpu(cpu)
> - WARN_ON_ONCE(!RB_EMPTY_ROOT(&cpu_rq(cpu)->core_tree));
> + WARN_ON_ONCE(cpu_rq(cpu)->cookied_count);
> }
>
> static void __sched_core_enable(void)
> @@ -2061,14 +2066,12 @@ static inline void enqueue_task(struct rq *rq, struct task_struct *p, int flags)
> uclamp_rq_inc(rq, p);
> p->sched_class->enqueue_task(rq, p, flags);
>
> - if (sched_core_enabled(rq))
> - sched_core_enqueue(rq, p);
> + sched_core_enqueue(rq, p);
> }
>
> static inline void dequeue_task(struct rq *rq, struct task_struct *p, int flags)
> {
> - if (sched_core_enabled(rq))
> - sched_core_dequeue(rq, p, flags);
> + sched_core_dequeue(rq, p, flags);
>
> if (!(flags & DEQUEUE_NOCLOCK))
> update_rq_clock(rq);
> @@ -6126,13 +6129,8 @@ pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
> rq_i = cpu_rq(i);
> p = rq_i->core_pick;
>
> - if (!cookie_equals(p, cookie)) {
> - p = NULL;
> - if (cookie)
> - p = sched_core_find(rq_i, cookie);
> - if (!p)
> - p = idle_sched_class.pick_task(rq_i);
> - }
> + if (!cookie_equals(p, cookie))
> + p = sched_core_find(rq_i, cookie);
>
> rq_i->core_pick = p;
>
> @@ -6333,6 +6331,7 @@ static void sched_core_cpu_starting(unsigned int cpu)
> sched_core_lock(cpu, &flags);
>
> WARN_ON_ONCE(rq->core != rq);
> + WARN_ON_ONCE(rq->cookied_count);
>
> /* if we're the first, we'll be our own leader */
> if (cpumask_weight(smt_mask) == 1)
> @@ -6425,6 +6424,7 @@ static inline void sched_core_cpu_dying(unsigned int cpu)
> {
> struct rq *rq = cpu_rq(cpu);
>
> + WARN_ON_ONCE(rq->cookied_count);
> if (rq->core != rq)
> rq->core = rq;
> }
> @@ -9917,6 +9917,7 @@ void __init sched_init(void)
> rq->core = rq;
> rq->core_pick = NULL;
> rq->core_enabled = 0;
> + rq->cookied_count = 0;
> rq->core_tree = RB_ROOT;
> rq->core_forceidle_count = 0;
> rq->core_forceidle_occupation = 0;
> diff --git a/kernel/sched/core_sched.c b/kernel/sched/core_sched.c
> index a57fd8f27498..70f424abcc2b 100644
> --- a/kernel/sched/core_sched.c
> +++ b/kernel/sched/core_sched.c
> @@ -56,6 +56,7 @@ static unsigned long sched_core_update_cookie(struct task_struct *p,
> unsigned long old_cookie;
> struct rq_flags rf;
> struct rq *rq;
> + bool enqueued;
>
> rq = task_rq_lock(p, &rf);
>
> @@ -67,16 +68,14 @@ static unsigned long sched_core_update_cookie(struct task_struct *p,
> */
> SCHED_WARN_ON((p->core_cookie || cookie) && !sched_core_enabled(rq));
>
> - if (sched_core_enqueued(p))
> + enqueued = task_on_rq_queued(p);
> + if (enqueued)
> sched_core_dequeue(rq, p, DEQUEUE_SAVE);
>
> old_cookie = p->core_cookie;
> p->core_cookie = cookie;
>
> - /*
> - * Consider the cases: !prev_cookie and !cookie.
> - */
> - if (cookie && task_on_rq_queued(p))
> + if (enqueued)
> sched_core_enqueue(rq, p);
>
> /*
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index 3e8df6d31c1e..f5a0ee7fccae 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -1148,6 +1148,7 @@ struct rq {
> unsigned int core_task_seq;
> unsigned int core_pick_seq;
> unsigned long core_cookie;
> + unsigned int cookied_count;
> unsigned int core_forceidle_count;
> unsigned int core_forceidle_seq;
> unsigned int core_forceidle_occupation;
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