From: Chengming Zhou <zhouchengming@bytedance.com>
To: hannes@cmpxchg.org, mingo@redhat.com, peterz@infradead.org,
juri.lelli@redhat.com, vincent.guittot@linaro.org,
rostedt@goodmis.org
Cc: linux-kernel@vger.kernel.org, songmuchun@bytedance.com,
zhouchengming@bytedance.com
Subject: [PATCH v2] psi: Optimize task switch inside shared cgroups
Date: Wed, 17 Feb 2021 13:48:03 +0800 [thread overview]
Message-ID: <20210217054803.77890-1-zhouchengming@bytedance.com> (raw)
The commit 36b238d57172 ("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.
Updates since v1:
- Many improvements in the comments and code from Johannes.
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>
---
kernel/sched/psi.c | 35 +++++++++++++++++++++++++----------
kernel/sched/stats.h | 28 ++++++++++++----------------
2 files changed, 37 insertions(+), 26 deletions(-)
diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
index 0fe6ff6a6a15..548d405bae3e 100644
--- a/kernel/sched/psi.c
+++ b/kernel/sched/psi.c
@@ -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);
+ }
}
}
diff --git a/kernel/sched/stats.h b/kernel/sched/stats.h
index 9e4e67a94731..dc218e9f4558 100644
--- a/kernel/sched/stats.h
+++ b/kernel/sched/stats.h
@@ -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) {
- 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;
+ /*
+ * 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_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)
--
2.11.0
reply other threads:[~2021-02-17 5:48 UTC|newest]
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