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sched/psi: Cache parent psi_group to speed up group iteration

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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@bytedance.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Link: https://lore.kernel.org/r/20220825164111.29534-10-zhouchengming@bytedance.com
This commit is contained in:
Chengming Zhou 2022-08-26 00:41:10 +08:00 committed by Peter Zijlstra
parent 57899a6610
commit dc86aba751
2 changed files with 21 additions and 30 deletions
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2
include/linux/psi_types.h
View File

@ -151,6 +151,8 @@ struct psi_trigger {
};
struct psi_group {
struct psi_group *parent;
/* Protects data used by the aggregator */
struct mutex avgs_lock;

49
kernel/sched/psi.c
View File

@ -772,27 +772,12 @@ 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;
}
@ -815,7 +800,6 @@ 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)
@ -825,8 +809,10 @@ 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);
do {
psi_group_change(group, cpu, clear, set, now, true);
} while ((group = group->parent));
}
void psi_task_switch(struct task_struct *prev, struct task_struct *next,
@ -834,7 +820,6 @@ 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) {
@ -844,8 +829,8 @@ void psi_task_switch(struct task_struct *prev, struct task_struct *next,
* ancestors with @prev, those will already have @prev's
* TSK_ONCPU bit set, and we can stop the iteration there.
*/
iter = NULL;
while ((group = iterate_groups(next, &iter))) {
group = task_psi_group(next);
do {
if (per_cpu_ptr(group->pcpu, cpu)->state_mask &
PSI_ONCPU) {
common = group;
@ -853,7 +838,7 @@ void psi_task_switch(struct task_struct *prev, struct task_struct *next,
}
psi_group_change(group, cpu, 0, TSK_ONCPU, now, true);
}
} while ((group = group->parent));
}
if (prev->pid) {
@ -886,9 +871,12 @@ 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);
do {
if (group == common)
break;
psi_group_change(group, cpu, clear, set, now, wake_clock);
} while ((group = group->parent));
/*
* TSK_ONCPU is handled up to the common ancestor. If there are
@ -898,7 +886,7 @@ void psi_task_switch(struct task_struct *prev, struct task_struct *next,
*/
if ((prev->psi_flags ^ next->psi_flags) & ~TSK_ONCPU) {
clear &= ~TSK_ONCPU;
for (; group; group = iterate_groups(prev, &iter))
for (; group; group = group->parent)
psi_group_change(group, cpu, clear, set, now, wake_clock);
}
}
@ -908,7 +896,6 @@ 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;
@ -918,7 +905,8 @@ 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);
do {
groupc = per_cpu_ptr(group->pcpu, cpu);
write_seqcount_begin(&groupc->seq);
@ -930,7 +918,7 @@ void psi_account_irqtime(struct task_struct *task, u32 delta)
if (group->poll_states & (1 << PSI_IRQ_FULL))
psi_schedule_poll_work(group, 1);
}
} while ((group = group->parent));
}
#endif
@ -1010,6 +998,7 @@ int psi_cgroup_alloc(struct cgroup *cgroup)
return -ENOMEM;
}
group_init(cgroup->psi);
cgroup->psi->parent = cgroup_psi(cgroup_parent(cgroup));
return 0;
}