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Commit 03582f33 authored by Linus Torvalds's avatar Linus Torvalds
Browse files

Merge branch 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 

Pull scheduler fix from Ingo Molnar:
 "Fix an exec() related scalability/performance regression, which was
  caused by incorrectly calculating load and migrating tasks on exec()
  when they shouldn't be"

* 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  sched/fair: Fix cpu_util_wake() for 'execl' type workloads
parents b53e27f6 c469933e

kernel/sched/fair.c

+48 −14
Original line number Diff line number Diff line
@@ -5674,11 +5674,11 @@ static int wake_affine(struct sched_domain *sd, struct task_struct *p, 
	return target;

}



static unsigned long cpu_util_wake(int cpu, struct task_struct *p);

static unsigned long cpu_util_without(int cpu, struct task_struct *p);



static unsigned long capacity_spare_wake(int cpu, struct task_struct *p)

static unsigned long capacity_spare_without(int cpu, struct task_struct *p)

{

	return max_t(long, capacity_of(cpu) - cpu_util_wake(cpu, p), 0);

	return max_t(long, capacity_of(cpu) - cpu_util_without(cpu, p), 0);

}



/*
@@ -5738,7 +5738,7 @@ find_idlest_group(struct sched_domain *sd, struct task_struct *p, 


			avg_load += cfs_rq_load_avg(&cpu_rq(i)->cfs);



			spare_cap = capacity_spare_wake(i, p);

			spare_cap = capacity_spare_without(i, p);



			if (spare_cap > max_spare_cap)

				max_spare_cap = spare_cap;
@@ -5889,8 +5889,8 @@ static inline int find_idlest_cpu(struct sched_domain *sd, struct task_struct *p 
		return prev_cpu;



	/*

	 * We need task's util for capacity_spare_wake, sync it up to prev_cpu's

	 * last_update_time.

	 * We need task's util for capacity_spare_without, sync it up to

	 * prev_cpu's last_update_time.

	 */

	if (!(sd_flag & SD_BALANCE_FORK))

		sync_entity_load_avg(&p->se);
@@ -6216,10 +6216,19 @@ static inline unsigned long cpu_util(int cpu) 
}



/*

 * cpu_util_wake: Compute CPU utilization with any contributions from

 * the waking task p removed.

 * cpu_util_without: compute cpu utilization without any contributions from *p

 * @cpu: the CPU which utilization is requested

 * @p: the task which utilization should be discounted

 *

 * The utilization of a CPU is defined by the utilization of tasks currently

 * enqueued on that CPU as well as tasks which are currently sleeping after an

 * execution on that CPU.

 *

 * This method returns the utilization of the specified CPU by discounting the

 * utilization of the specified task, whenever the task is currently

 * contributing to the CPU utilization.

 */

static unsigned long cpu_util_wake(int cpu, struct task_struct *p)

static unsigned long cpu_util_without(int cpu, struct task_struct *p)

{

	struct cfs_rq *cfs_rq;

	unsigned int util;
@@ -6231,7 +6240,7 @@ static unsigned long cpu_util_wake(int cpu, struct task_struct *p) 
	cfs_rq = &cpu_rq(cpu)->cfs;

	util = READ_ONCE(cfs_rq->avg.util_avg);



	/* Discount task's blocked util from CPU's util */

	/* Discount task's util from CPU's util */

	util -= min_t(unsigned int, util, task_util(p));



	/*
@@ -6240,14 +6249,14 @@ static unsigned long cpu_util_wake(int cpu, struct task_struct *p) 
	 * a) if *p is the only task sleeping on this CPU, then:

	 *      cpu_util (== task_util) > util_est (== 0)

	 *    and thus we return:

	 *      cpu_util_wake = (cpu_util - task_util) = 0

	 *      cpu_util_without = (cpu_util - task_util) = 0

	 *

	 * b) if other tasks are SLEEPING on this CPU, which is now exiting

	 *    IDLE, then:

	 *      cpu_util >= task_util

	 *      cpu_util > util_est (== 0)

	 *    and thus we discount *p's blocked utilization to return:

	 *      cpu_util_wake = (cpu_util - task_util) >= 0

	 *      cpu_util_without = (cpu_util - task_util) >= 0

	 *

	 * c) if other tasks are RUNNABLE on that CPU and

	 *      util_est > cpu_util
@@ -6260,8 +6269,33 @@ static unsigned long cpu_util_wake(int cpu, struct task_struct *p) 
	 * covered by the following code when estimated utilization is

	 * enabled.

	 */

	if (sched_feat(UTIL_EST))

		util = max(util, READ_ONCE(cfs_rq->avg.util_est.enqueued));

	if (sched_feat(UTIL_EST)) {

		unsigned int estimated =

			READ_ONCE(cfs_rq->avg.util_est.enqueued);



		/*

		 * Despite the following checks we still have a small window

		 * for a possible race, when an execl's select_task_rq_fair()

		 * races with LB's detach_task():

		 *

		 *   detach_task()

		 *     p->on_rq = TASK_ON_RQ_MIGRATING;

		 *     ---------------------------------- A

		 *     deactivate_task()                   \

		 *       dequeue_task()                     + RaceTime

		 *         util_est_dequeue()              /

		 *     ---------------------------------- B

		 *

		 * The additional check on "current == p" it's required to

		 * properly fix the execl regression and it helps in further

		 * reducing the chances for the above race.

		 */

		if (unlikely(task_on_rq_queued(p) || current == p)) {

			estimated -= min_t(unsigned int, estimated,

					   (_task_util_est(p) | UTIL_AVG_UNCHANGED));

		}

		util = max(util, estimated);

	}



	/*

	 * Utilization (estimated) can exceed the CPU capacity, thus let's