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Date: Wed, 24 Aug 2022 16:18:28 +0800
From: Chengming Zhou <zhouchengming@...edance.com>
To: tj@...nel.org, hannes@...xchg.org, mkoutny@...e.com,
surenb@...gle.com
Cc: gregkh@...uxfoundation.org, corbet@....net, mingo@...hat.com,
peterz@...radead.org, songmuchun@...edance.com,
cgroups@...r.kernel.org, linux-doc@...r.kernel.org,
linux-kernel@...r.kernel.org,
Chengming Zhou <zhouchengming@...edance.com>
Subject: [PATCH v3 09/10] sched/psi: cache parent psi_group to speed up groups iterate
We use iterate_groups() to iterate each level psi_group to update
PSI stats, which is a very hot path.
In current code, iterate_groups() have to use multiple branches and
cgroup_parent() to get parent psi_group for each level, which is not
very efficient.
This patch cache parent psi_group in struct psi_group, only need to get
psi_group of task itself first, then just use group->parent to iterate.
Signed-off-by: Chengming Zhou <zhouchengming@...edance.com>
---
include/linux/psi_types.h | 2 ++
kernel/sched/psi.c | 47 ++++++++++++++++-----------------------
2 files changed, 21 insertions(+), 28 deletions(-)
diff --git a/include/linux/psi_types.h b/include/linux/psi_types.h
index 40c28171cd91..a0b746258c68 100644
--- a/include/linux/psi_types.h
+++ b/include/linux/psi_types.h
@@ -151,6 +151,8 @@ struct psi_trigger {
};
struct psi_group {
+ struct psi_group *parent;
+
/* Protects data used by the aggregator */
struct mutex avgs_lock;
diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
index 7aab6f13ed12..814e99b1fed3 100644
--- a/kernel/sched/psi.c
+++ b/kernel/sched/psi.c
@@ -772,30 +772,18 @@ static void psi_group_change(struct psi_group *group, int cpu,
schedule_delayed_work(&group->avgs_work, PSI_FREQ);
}
-static struct psi_group *iterate_groups(struct task_struct *task, void **iter)
+static inline struct psi_group *task_psi_group(struct task_struct *task)
{
- if (*iter == &psi_system)
- return NULL;
-
#ifdef CONFIG_CGROUPS
- if (static_branch_likely(&psi_cgroups_enabled)) {
- struct cgroup *cgroup = NULL;
-
- if (!*iter)
- cgroup = task->cgroups->dfl_cgrp;
- else
- cgroup = cgroup_parent(*iter);
-
- if (cgroup && cgroup_parent(cgroup)) {
- *iter = cgroup;
- return cgroup_psi(cgroup);
- }
- }
+ if (static_branch_likely(&psi_cgroups_enabled))
+ return cgroup_psi(task_dfl_cgroup(task));
#endif
- *iter = &psi_system;
return &psi_system;
}
+#define for_each_psi_group(group) \
+ for (; group; group = group->parent)
+
static void psi_flags_change(struct task_struct *task, int clear, int set)
{
if (((task->psi_flags & set) ||
@@ -815,7 +803,6 @@ void psi_task_change(struct task_struct *task, int clear, int set)
{
int cpu = task_cpu(task);
struct psi_group *group;
- void *iter = NULL;
u64 now;
if (!task->pid)
@@ -825,7 +812,8 @@ void psi_task_change(struct task_struct *task, int clear, int set)
now = cpu_clock(cpu);
- while ((group = iterate_groups(task, &iter)))
+ group = task_psi_group(task);
+ for_each_psi_group(group)
psi_group_change(group, cpu, clear, set, now, true);
}
@@ -834,7 +822,6 @@ void psi_task_switch(struct task_struct *prev, struct task_struct *next,
{
struct psi_group *group, *common = NULL;
int cpu = task_cpu(prev);
- void *iter;
u64 now = cpu_clock(cpu);
if (next->pid) {
@@ -845,8 +832,8 @@ void psi_task_switch(struct task_struct *prev, struct task_struct *next,
* we reach the first common ancestor. Iterate @next's
* ancestors only until we encounter @prev's ONCPU.
*/
- iter = NULL;
- while ((group = iterate_groups(next, &iter))) {
+ group = task_psi_group(next);
+ for_each_psi_group(group) {
if (per_cpu_ptr(group->pcpu, cpu)->state_mask &
PSI_ONCPU) {
common = group;
@@ -887,9 +874,12 @@ void psi_task_switch(struct task_struct *prev, struct task_struct *next,
psi_flags_change(prev, clear, set);
- iter = NULL;
- while ((group = iterate_groups(prev, &iter)) && group != common)
+ group = task_psi_group(prev);
+ for_each_psi_group(group) {
+ if (group == common)
+ break;
psi_group_change(group, cpu, clear, set, now, wake_clock);
+ }
/*
* TSK_ONCPU is handled up to the common ancestor. If we're tasked
@@ -897,7 +887,7 @@ void psi_task_switch(struct task_struct *prev, struct task_struct *next,
*/
if (sleep || unlikely(prev->in_memstall != next->in_memstall)) {
clear &= ~TSK_ONCPU;
- for (; group; group = iterate_groups(prev, &iter))
+ for_each_psi_group(group)
psi_group_change(group, cpu, clear, set, now, wake_clock);
}
}
@@ -907,7 +897,6 @@ void psi_task_switch(struct task_struct *prev, struct task_struct *next,
void psi_account_irqtime(struct task_struct *task, u32 delta)
{
int cpu = task_cpu(task);
- void *iter = NULL;
struct psi_group *group;
struct psi_group_cpu *groupc;
u64 now;
@@ -917,7 +906,8 @@ void psi_account_irqtime(struct task_struct *task, u32 delta)
now = cpu_clock(cpu);
- while ((group = iterate_groups(task, &iter))) {
+ group = task_psi_group(task);
+ for_each_psi_group(group) {
groupc = per_cpu_ptr(group->pcpu, cpu);
write_seqcount_begin(&groupc->seq);
@@ -1009,6 +999,7 @@ int psi_cgroup_alloc(struct cgroup *cgroup)
return -ENOMEM;
}
group_init(cgroup->psi);
+ cgroup->psi->parent = cgroup_psi(cgroup_parent(cgroup));
return 0;
}
--
2.37.2
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