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psi: Optimize task switch inside shared cgroups

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The commit 36b238d571 ("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: Muchun Song <songmuchun@bytedance.com>
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Link: https://lkml.kernel.org/r/20210303034659.91735-5-zhouchengming@bytedance.com
This commit is contained in:
Chengming Zhou 2021-03-03 11:46:59 +08:00 committed by Ingo Molnar
parent fddc8bab53
commit 4117cebf1a
2 changed files with 37 additions and 26 deletions
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35
kernel/sched/psi.c
View File

@ -840,20 +840,35 @@ void psi_task_switch(struct task_struct *prev, struct task_struct *next,
}
}
/*
* 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.
*/
if (sleep)
return;
if (prev->pid) {
psi_flags_change(prev, TSK_ONCPU, 0);
int clear = TSK_ONCPU, set = 0;
/*
* 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) {
clear |= TSK_RUNNING;
if (prev->in_iowait)
set |= TSK_IOWAIT;
}
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);
}
}
}

26
kernel/sched/stats.h
View File

@ -84,28 +84,24 @@ 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) {
/*
* 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.
*/
if (sleep)
return;
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().
*/
clear |= TSK_ONCPU;
if (p->in_iowait)
set |= TSK_IOWAIT;
}
psi_task_change(p, clear, set);
psi_task_change(p, clear, 0);
}
static inline void psi_ttwu_dequeue(struct task_struct *p)