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linux-next/kernel/cgroup/rstat.c
Tejun Heo c43c5ea75f cgroup: Make cgroup_rstat_updated() ready for root cgroup usage
cgroup_rstat_updated() ensures that the cgroup's rstat is linked to
the parent.  If there's no parent, it never gets linked and the
function ends up grabbing and releasing the cgroup_rstat_lock each
time for no reason which can be expensive.

This hasn't been a problem till now because nobody was calling the
function for the root cgroup but rstat is gonna be exposed to
controllers and use cases, so let's get ready.  Make
cgroup_rstat_updated() an no-op for the root cgroup.

Signed-off-by: Tejun Heo <tj@kernel.org>
2018-04-26 14:29:06 -07:00

417 lines
11 KiB
C

#include "cgroup-internal.h"
#include <linux/sched/cputime.h>
static DEFINE_SPINLOCK(cgroup_rstat_lock);
static DEFINE_PER_CPU(raw_spinlock_t, cgroup_rstat_cpu_lock);
static void cgroup_base_stat_flush(struct cgroup *cgrp, int cpu);
static struct cgroup_rstat_cpu *cgroup_rstat_cpu(struct cgroup *cgrp, int cpu)
{
return per_cpu_ptr(cgrp->rstat_cpu, cpu);
}
/**
* cgroup_rstat_updated - keep track of updated rstat_cpu
* @cgrp: target cgroup
* @cpu: cpu on which rstat_cpu was updated
*
* @cgrp's rstat_cpu on @cpu was updated. Put it on the parent's matching
* rstat_cpu->updated_children list. See the comment on top of
* cgroup_rstat_cpu definition for details.
*/
void cgroup_rstat_updated(struct cgroup *cgrp, int cpu)
{
raw_spinlock_t *cpu_lock = per_cpu_ptr(&cgroup_rstat_cpu_lock, cpu);
struct cgroup *parent;
unsigned long flags;
/* nothing to do for root */
if (!cgroup_parent(cgrp))
return;
/*
* Paired with the one in cgroup_rstat_cpu_pop_upated(). Either we
* see NULL updated_next or they see our updated stat.
*/
smp_mb();
/*
* Because @parent's updated_children is terminated with @parent
* instead of NULL, we can tell whether @cgrp is on the list by
* testing the next pointer for NULL.
*/
if (cgroup_rstat_cpu(cgrp, cpu)->updated_next)
return;
raw_spin_lock_irqsave(cpu_lock, flags);
/* put @cgrp and all ancestors on the corresponding updated lists */
for (parent = cgroup_parent(cgrp); parent;
cgrp = parent, parent = cgroup_parent(cgrp)) {
struct cgroup_rstat_cpu *rstatc = cgroup_rstat_cpu(cgrp, cpu);
struct cgroup_rstat_cpu *prstatc = cgroup_rstat_cpu(parent, cpu);
/*
* Both additions and removals are bottom-up. If a cgroup
* is already in the tree, all ancestors are.
*/
if (rstatc->updated_next)
break;
rstatc->updated_next = prstatc->updated_children;
prstatc->updated_children = cgrp;
}
raw_spin_unlock_irqrestore(cpu_lock, flags);
}
EXPORT_SYMBOL_GPL(cgroup_rstat_updated);
/**
* cgroup_rstat_cpu_pop_updated - iterate and dismantle rstat_cpu updated tree
* @pos: current position
* @root: root of the tree to traversal
* @cpu: target cpu
*
* Walks the udpated rstat_cpu tree on @cpu from @root. %NULL @pos starts
* the traversal and %NULL return indicates the end. During traversal,
* each returned cgroup is unlinked from the tree. Must be called with the
* matching cgroup_rstat_cpu_lock held.
*
* The only ordering guarantee is that, for a parent and a child pair
* covered by a given traversal, if a child is visited, its parent is
* guaranteed to be visited afterwards.
*/
static struct cgroup *cgroup_rstat_cpu_pop_updated(struct cgroup *pos,
struct cgroup *root, int cpu)
{
struct cgroup_rstat_cpu *rstatc;
struct cgroup *parent;
if (pos == root)
return NULL;
/*
* We're gonna walk down to the first leaf and visit/remove it. We
* can pick whatever unvisited node as the starting point.
*/
if (!pos)
pos = root;
else
pos = cgroup_parent(pos);
/* walk down to the first leaf */
while (true) {
rstatc = cgroup_rstat_cpu(pos, cpu);
if (rstatc->updated_children == pos)
break;
pos = rstatc->updated_children;
}
/*
* Unlink @pos from the tree. As the updated_children list is
* singly linked, we have to walk it to find the removal point.
* However, due to the way we traverse, @pos will be the first
* child in most cases. The only exception is @root.
*/
parent = cgroup_parent(pos);
if (parent && rstatc->updated_next) {
struct cgroup_rstat_cpu *prstatc = cgroup_rstat_cpu(parent, cpu);
struct cgroup_rstat_cpu *nrstatc;
struct cgroup **nextp;
nextp = &prstatc->updated_children;
while (true) {
nrstatc = cgroup_rstat_cpu(*nextp, cpu);
if (*nextp == pos)
break;
WARN_ON_ONCE(*nextp == parent);
nextp = &nrstatc->updated_next;
}
*nextp = rstatc->updated_next;
rstatc->updated_next = NULL;
/*
* Paired with the one in cgroup_rstat_cpu_updated().
* Either they see NULL updated_next or we see their
* updated stat.
*/
smp_mb();
}
return pos;
}
/* see cgroup_rstat_flush() */
static void cgroup_rstat_flush_locked(struct cgroup *cgrp, bool may_sleep)
__releases(&cgroup_rstat_lock) __acquires(&cgroup_rstat_lock)
{
int cpu;
lockdep_assert_held(&cgroup_rstat_lock);
for_each_possible_cpu(cpu) {
raw_spinlock_t *cpu_lock = per_cpu_ptr(&cgroup_rstat_cpu_lock,
cpu);
struct cgroup *pos = NULL;
raw_spin_lock(cpu_lock);
while ((pos = cgroup_rstat_cpu_pop_updated(pos, cgrp, cpu))) {
struct cgroup_subsys_state *css;
cgroup_base_stat_flush(pos, cpu);
rcu_read_lock();
list_for_each_entry_rcu(css, &pos->rstat_css_list,
rstat_css_node)
css->ss->css_rstat_flush(css, cpu);
rcu_read_unlock();
}
raw_spin_unlock(cpu_lock);
/* if @may_sleep, play nice and yield if necessary */
if (may_sleep && (need_resched() ||
spin_needbreak(&cgroup_rstat_lock))) {
spin_unlock_irq(&cgroup_rstat_lock);
if (!cond_resched())
cpu_relax();
spin_lock_irq(&cgroup_rstat_lock);
}
}
}
/**
* cgroup_rstat_flush - flush stats in @cgrp's subtree
* @cgrp: target cgroup
*
* Collect all per-cpu stats in @cgrp's subtree into the global counters
* and propagate them upwards. After this function returns, all cgroups in
* the subtree have up-to-date ->stat.
*
* This also gets all cgroups in the subtree including @cgrp off the
* ->updated_children lists.
*
* This function may block.
*/
void cgroup_rstat_flush(struct cgroup *cgrp)
{
might_sleep();
spin_lock_irq(&cgroup_rstat_lock);
cgroup_rstat_flush_locked(cgrp, true);
spin_unlock_irq(&cgroup_rstat_lock);
}
/**
* cgroup_rstat_flush_irqsafe - irqsafe version of cgroup_rstat_flush()
* @cgrp: target cgroup
*
* This function can be called from any context.
*/
void cgroup_rstat_flush_irqsafe(struct cgroup *cgrp)
{
unsigned long flags;
spin_lock_irqsave(&cgroup_rstat_lock, flags);
cgroup_rstat_flush_locked(cgrp, false);
spin_unlock_irqrestore(&cgroup_rstat_lock, flags);
}
/**
* cgroup_rstat_flush_begin - flush stats in @cgrp's subtree and hold
* @cgrp: target cgroup
*
* Flush stats in @cgrp's subtree and prevent further flushes. Must be
* paired with cgroup_rstat_flush_release().
*
* This function may block.
*/
void cgroup_rstat_flush_hold(struct cgroup *cgrp)
__acquires(&cgroup_rstat_lock)
{
might_sleep();
spin_lock_irq(&cgroup_rstat_lock);
cgroup_rstat_flush_locked(cgrp, true);
}
/**
* cgroup_rstat_flush_release - release cgroup_rstat_flush_hold()
*/
void cgroup_rstat_flush_release(void)
__releases(&cgroup_rstat_lock)
{
spin_unlock_irq(&cgroup_rstat_lock);
}
int cgroup_rstat_init(struct cgroup *cgrp)
{
int cpu;
/* the root cgrp has rstat_cpu preallocated */
if (!cgrp->rstat_cpu) {
cgrp->rstat_cpu = alloc_percpu(struct cgroup_rstat_cpu);
if (!cgrp->rstat_cpu)
return -ENOMEM;
}
/* ->updated_children list is self terminated */
for_each_possible_cpu(cpu) {
struct cgroup_rstat_cpu *rstatc = cgroup_rstat_cpu(cgrp, cpu);
rstatc->updated_children = cgrp;
u64_stats_init(&rstatc->bsync);
}
return 0;
}
void cgroup_rstat_exit(struct cgroup *cgrp)
{
int cpu;
cgroup_rstat_flush(cgrp);
/* sanity check */
for_each_possible_cpu(cpu) {
struct cgroup_rstat_cpu *rstatc = cgroup_rstat_cpu(cgrp, cpu);
if (WARN_ON_ONCE(rstatc->updated_children != cgrp) ||
WARN_ON_ONCE(rstatc->updated_next))
return;
}
free_percpu(cgrp->rstat_cpu);
cgrp->rstat_cpu = NULL;
}
void __init cgroup_rstat_boot(void)
{
int cpu;
for_each_possible_cpu(cpu)
raw_spin_lock_init(per_cpu_ptr(&cgroup_rstat_cpu_lock, cpu));
BUG_ON(cgroup_rstat_init(&cgrp_dfl_root.cgrp));
}
/*
* Functions for cgroup basic resource statistics implemented on top of
* rstat.
*/
static void cgroup_base_stat_accumulate(struct cgroup_base_stat *dst_bstat,
struct cgroup_base_stat *src_bstat)
{
dst_bstat->cputime.utime += src_bstat->cputime.utime;
dst_bstat->cputime.stime += src_bstat->cputime.stime;
dst_bstat->cputime.sum_exec_runtime += src_bstat->cputime.sum_exec_runtime;
}
static void cgroup_base_stat_flush(struct cgroup *cgrp, int cpu)
{
struct cgroup *parent = cgroup_parent(cgrp);
struct cgroup_rstat_cpu *rstatc = cgroup_rstat_cpu(cgrp, cpu);
struct task_cputime *last_cputime = &rstatc->last_bstat.cputime;
struct task_cputime cputime;
struct cgroup_base_stat delta;
unsigned seq;
/* fetch the current per-cpu values */
do {
seq = __u64_stats_fetch_begin(&rstatc->bsync);
cputime = rstatc->bstat.cputime;
} while (__u64_stats_fetch_retry(&rstatc->bsync, seq));
/* calculate the delta to propgate */
delta.cputime.utime = cputime.utime - last_cputime->utime;
delta.cputime.stime = cputime.stime - last_cputime->stime;
delta.cputime.sum_exec_runtime = cputime.sum_exec_runtime -
last_cputime->sum_exec_runtime;
*last_cputime = cputime;
/* transfer the pending stat into delta */
cgroup_base_stat_accumulate(&delta, &cgrp->pending_bstat);
memset(&cgrp->pending_bstat, 0, sizeof(cgrp->pending_bstat));
/* propagate delta into the global stat and the parent's pending */
cgroup_base_stat_accumulate(&cgrp->bstat, &delta);
if (parent)
cgroup_base_stat_accumulate(&parent->pending_bstat, &delta);
}
static struct cgroup_rstat_cpu *
cgroup_base_stat_cputime_account_begin(struct cgroup *cgrp)
{
struct cgroup_rstat_cpu *rstatc;
rstatc = get_cpu_ptr(cgrp->rstat_cpu);
u64_stats_update_begin(&rstatc->bsync);
return rstatc;
}
static void cgroup_base_stat_cputime_account_end(struct cgroup *cgrp,
struct cgroup_rstat_cpu *rstatc)
{
u64_stats_update_end(&rstatc->bsync);
cgroup_rstat_updated(cgrp, smp_processor_id());
put_cpu_ptr(rstatc);
}
void __cgroup_account_cputime(struct cgroup *cgrp, u64 delta_exec)
{
struct cgroup_rstat_cpu *rstatc;
rstatc = cgroup_base_stat_cputime_account_begin(cgrp);
rstatc->bstat.cputime.sum_exec_runtime += delta_exec;
cgroup_base_stat_cputime_account_end(cgrp, rstatc);
}
void __cgroup_account_cputime_field(struct cgroup *cgrp,
enum cpu_usage_stat index, u64 delta_exec)
{
struct cgroup_rstat_cpu *rstatc;
rstatc = cgroup_base_stat_cputime_account_begin(cgrp);
switch (index) {
case CPUTIME_USER:
case CPUTIME_NICE:
rstatc->bstat.cputime.utime += delta_exec;
break;
case CPUTIME_SYSTEM:
case CPUTIME_IRQ:
case CPUTIME_SOFTIRQ:
rstatc->bstat.cputime.stime += delta_exec;
break;
default:
break;
}
cgroup_base_stat_cputime_account_end(cgrp, rstatc);
}
void cgroup_base_stat_cputime_show(struct seq_file *seq)
{
struct cgroup *cgrp = seq_css(seq)->cgroup;
u64 usage, utime, stime;
if (!cgroup_parent(cgrp))
return;
cgroup_rstat_flush_hold(cgrp);
usage = cgrp->bstat.cputime.sum_exec_runtime;
cputime_adjust(&cgrp->bstat.cputime, &cgrp->prev_cputime, &utime, &stime);
cgroup_rstat_flush_release();
do_div(usage, NSEC_PER_USEC);
do_div(utime, NSEC_PER_USEC);
do_div(stime, NSEC_PER_USEC);
seq_printf(seq, "usage_usec %llu\n"
"user_usec %llu\n"
"system_usec %llu\n",
usage, utime, stime);
}