Commit 243f7845 authored by Chengming Zhou's avatar Chengming Zhou Committed by Zheng Zengkai
Browse files

psi: Optimize task switch inside shared cgroups 

mainline inclusion
from mainline-v5.13-rc1
commit 4117cebf
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I562O9
CVE: NA
backport: openEuler-22.03-LTS

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=4117cebf1a9fcbf35b9aabf0e37b6c5eea296798



--------------------------------

The commit 36b238d5 ("psi: Optimize switching tasks inside shared
cgroups") only update cgroups whose state actually changes during a
task switch only in task preempt case, not in task sleep case.

We actually don't need to clear and set TSK_ONCPU state for common cgroups
of next and prev task in sleep case, that can save many psi_group_change
especially when most activity comes from one leaf cgroup.

sleep before:
psi_dequeue()
  while ((group = iterate_groups(prev)))  # all ancestors
    psi_group_change(prev, .clear=TSK_RUNNING|TSK_ONCPU)
psi_task_switch()
  while ((group = iterate_groups(next)))  # all ancestors
    psi_group_change(next, .set=TSK_ONCPU)

sleep after:
psi_dequeue()
  nop
psi_task_switch()
  while ((group = iterate_groups(next)))  # until (prev & next)
    psi_group_change(next, .set=TSK_ONCPU)
  while ((group = iterate_groups(prev)))  # all ancestors
    psi_group_change(prev, .clear=common?TSK_RUNNING:TSK_RUNNING|TSK_ONCPU)

When a voluntary sleep switches to another task, we remove one call of
psi_group_change() for every common cgroup ancestor of the two tasks.

Co-developed-by: default avatarMuchun Song <songmuchun@bytedance.com>
Signed-off-by: default avatarMuchun Song <songmuchun@bytedance.com>
Signed-off-by: default avatarChengming Zhou <zhouchengming@bytedance.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
Acked-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
Link: https://lkml.kernel.org/r/20210303034659.91735-5-zhouchengming@bytedance.com


Signed-off-by: default avatarChen Wandun <chenwandun@huawei.com>
Reviewed-by: default avatarKefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: default avatarZheng Zengkai <zhengzengkai@huawei.com>
parent 69091428

kernel/sched/psi.c

+25 −10
Original line number Diff line number Diff line
@@ -862,20 +862,35 @@ void psi_task_switch(struct task_struct *prev, struct task_struct *next, 
		}

	}



	if (prev->pid) {

		int clear = TSK_ONCPU, set = 0;



		/*

	 * If this is a voluntary sleep, dequeue will have taken care

	 * of the outgoing TSK_ONCPU alongside TSK_RUNNING already. We

	 * only need to deal with it during preemption.

		 * When we're going to sleep, psi_dequeue() lets us handle

		 * TSK_RUNNING and TSK_IOWAIT here, where we can combine it

		 * with TSK_ONCPU and save walking common ancestors twice.

		 */

	if (sleep)

		return;

		if (sleep) {

			clear |= TSK_RUNNING;

			if (prev->in_iowait)

				set |= TSK_IOWAIT;

		}



	if (prev->pid) {

		psi_flags_change(prev, TSK_ONCPU, 0);

		psi_flags_change(prev, clear, set);



		iter = NULL;

		while ((group = iterate_groups(prev, &iter)) && group != common)

			psi_group_change(group, cpu, TSK_ONCPU, 0, true);

			psi_group_change(group, cpu, clear, set, true);



		/*

		 * TSK_ONCPU is handled up to the common ancestor. If we're tasked

		 * with dequeuing too, finish that for the rest of the hierarchy.

		 */

		if (sleep) {

			clear &= ~TSK_ONCPU;

			for (; group; group = iterate_groups(prev, &iter))

				psi_group_change(group, cpu, clear, set, true);

		}

	}

}

kernel/sched/stats.h

+12 −16
Original line number Diff line number Diff line
@@ -104,28 +104,24 @@ static inline void psi_enqueue(struct task_struct *p, bool wakeup) 


static inline void psi_dequeue(struct task_struct *p, bool sleep)

{

	int clear = TSK_RUNNING, set = 0;

	int clear = TSK_RUNNING;



	if (static_branch_likely(&psi_disabled))

		return;



	if (!sleep) {

		if (p->in_memstall)

			clear |= TSK_MEMSTALL;

	} else {

	/*

		 * When a task sleeps, schedule() dequeues it before

		 * switching to the next one. Merge the clearing of

		 * TSK_RUNNING and TSK_ONCPU to save an unnecessary

		 * psi_task_change() call in psi_sched_switch().

	 * A voluntary sleep is a dequeue followed by a task switch. To

	 * avoid walking all ancestors twice, psi_task_switch() handles

	 * TSK_RUNNING and TSK_IOWAIT for us when it moves TSK_ONCPU.

	 * Do nothing here.

	 */

		clear |= TSK_ONCPU;

	if (sleep)

		return;



		if (p->in_iowait)

			set |= TSK_IOWAIT;

	}

	if (p->in_memstall)

		clear |= TSK_MEMSTALL;



	psi_task_change(p, clear, set);

	psi_task_change(p, clear, 0);

}



static inline void psi_ttwu_dequeue(struct task_struct *p)