It is possible to eliminate contention between subsystems when
updating/flushing stats by using subsystem-specific locks. Let the existing
rstat locks be dedicated to the base stats and rename them to reflect it.
Add similar locks to the cgroup_subsys struct for use with individual
subsystems. To make use of the new locks, change the existing lock helper
functions to accept a reference to a css and use css->ss to access the
locks or use the static locks for base stats when css->ss is NULL.
Signed-off-by: JP Kobryn <inwardvessel@xxxxxxxxx>
---
block/blk-cgroup.c | 2 +-
include/linux/cgroup-defs.h | 12 ++-
include/trace/events/cgroup.h | 10 ++-
kernel/cgroup/cgroup-internal.h | 2 +-
kernel/cgroup/cgroup.c | 10 ++-
kernel/cgroup/rstat.c | 145 +++++++++++++++++++++-----------
6 files changed, 122 insertions(+), 59 deletions(-)
diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index cd9521f4f607..34d72bbdd5e5 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -1022,7 +1022,7 @@ static void __blkcg_rstat_flush(struct blkcg *blkcg, int cpu)
/*
* For covering concurrent parent blkg update from blkg_release().
*
- * When flushing from cgroup, cgroup_rstat_lock is always held, so
+ * When flushing from cgroup, the subsystem lock is always held, so
* this lock won't cause contention most of time.
*/
raw_spin_lock_irqsave(&blkg_stat_lock, flags);
diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h
index 031f55a9ac49..0ffc8438c6d9 100644
--- a/include/linux/cgroup-defs.h
+++ b/include/linux/cgroup-defs.h
@@ -223,7 +223,10 @@ struct cgroup_subsys_state {
/*
* A singly-linked list of css structures to be rstat flushed.
* This is a scratch field to be used exclusively by
- * cgroup_rstat_flush_locked() and protected by cgroup_rstat_lock.
+ * cgroup_rstat_flush_locked().
+ *
+ * protected by rstat_base_lock when css is cgroup::self
+ * protected by css->ss->lock otherwise
*/
struct cgroup_subsys_state *rstat_flush_next;
};
@@ -391,7 +394,9 @@ struct css_rstat_cpu {
* to the cgroup makes it unnecessary for each per-cpu struct to
* point back to the associated cgroup.
*
- * Protected by per-cpu cgroup_rstat_cpu_lock.
+ * Protected by per-cpu rstat_base_cpu_lock when css->ss == NULL
+ * otherwise,
+ * Protected by per-cpu css->ss->rstat_cpu_lock
*/
struct cgroup_subsys_state *updated_children; /* terminated by self */
struct cgroup_subsys_state *updated_next; /* NULL if not on list */
@@ -779,6 +784,9 @@ struct cgroup_subsys {
* specifies the mask of subsystems that this one depends on.
*/
unsigned int depends_on;
+
+ spinlock_t lock;
+ raw_spinlock_t __percpu *percpu_lock;
};
extern struct percpu_rw_semaphore cgroup_threadgroup_rwsem;
diff --git a/include/trace/events/cgroup.h b/include/trace/events/cgroup.h
index af2755bda6eb..ec3a95bf4981 100644
--- a/include/trace/events/cgroup.h
+++ b/include/trace/events/cgroup.h
@@ -231,7 +231,10 @@ DECLARE_EVENT_CLASS(cgroup_rstat,
__entry->cpu, __entry->contended)
);
-/* Related to global: cgroup_rstat_lock */
+/* Related to locks:
+ * rstat_base_lock when handling cgroup::self
+ * css->ss->lock otherwise
+ */
DEFINE_EVENT(cgroup_rstat, cgroup_rstat_lock_contended,
TP_PROTO(struct cgroup *cgrp, int cpu, bool contended),
@@ -253,7 +256,10 @@ DEFINE_EVENT(cgroup_rstat, cgroup_rstat_unlock,
TP_ARGS(cgrp, cpu, contended)
);
-/* Related to per CPU: cgroup_rstat_cpu_lock */
+/* Related to per CPU locks:
+ * rstat_base_cpu_lock when handling cgroup::self
+ * css->ss->cpu_lock otherwise
+ */
DEFINE_EVENT(cgroup_rstat, cgroup_rstat_cpu_lock_contended,
TP_PROTO(struct cgroup *cgrp, int cpu, bool contended),
diff --git a/kernel/cgroup/cgroup-internal.h b/kernel/cgroup/cgroup-internal.h
index d4b75fba9a54..513bfce3bc23 100644
--- a/kernel/cgroup/cgroup-internal.h
+++ b/kernel/cgroup/cgroup-internal.h
@@ -271,7 +271,7 @@ int cgroup_task_count(const struct cgroup *cgrp);
*/
int css_rstat_init(struct cgroup_subsys_state *css);
void css_rstat_exit(struct cgroup_subsys_state *css);
-void cgroup_rstat_boot(void);
+int ss_rstat_init(struct cgroup_subsys *ss);
void cgroup_base_stat_cputime_show(struct seq_file *seq);
/*
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 1e21065dec0e..3e8948805f67 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -6085,8 +6085,10 @@ static void __init cgroup_init_subsys(struct cgroup_subsys *ss, bool early)
css->id = cgroup_idr_alloc(&ss->css_idr, css, 1, 2, GFP_KERNEL);
BUG_ON(css->id < 0);
- if (ss->css_rstat_flush)
+ if (ss->css_rstat_flush) {
+ BUG_ON(ss_rstat_init(ss));
BUG_ON(css_rstat_init(css));
+ }
}
/* Update the init_css_set to contain a subsys
@@ -6163,7 +6165,7 @@ int __init cgroup_init(void)
BUG_ON(cgroup_init_cftypes(NULL, cgroup_psi_files));
BUG_ON(cgroup_init_cftypes(NULL, cgroup1_base_files));
- cgroup_rstat_boot();
+ BUG_ON(ss_rstat_init(NULL));
get_user_ns(init_cgroup_ns.user_ns);
@@ -6193,8 +6195,10 @@ int __init cgroup_init(void)
GFP_KERNEL);
BUG_ON(css->id < 0);
- if (ss->css_rstat_flush)
+ if (ss->css_rstat_flush) {
+ BUG_ON(ss_rstat_init(ss));
BUG_ON(css_rstat_init(css));
+ }
} else {
cgroup_init_subsys(ss, false);
}
diff --git a/kernel/cgroup/rstat.c b/kernel/cgroup/rstat.c
index a28c00b11736..ffd7ac6bcefc 100644
--- a/kernel/cgroup/rstat.c
+++ b/kernel/cgroup/rstat.c
@@ -9,8 +9,8 @@
#include <trace/events/cgroup.h>
-static DEFINE_SPINLOCK(cgroup_rstat_lock);
-static DEFINE_PER_CPU(raw_spinlock_t, cgroup_rstat_cpu_lock);
+static DEFINE_SPINLOCK(rstat_base_lock);
+static DEFINE_PER_CPU(raw_spinlock_t, rstat_base_cpu_lock);
static void cgroup_base_stat_flush(struct cgroup *cgrp, int cpu);
@@ -20,8 +20,24 @@ static struct css_rstat_cpu *css_rstat_cpu(
return per_cpu_ptr(css->rstat_cpu, cpu);
}
+static spinlock_t *ss_rstat_lock(struct cgroup_subsys *ss)
+{
+ if (ss)
+ return &ss->lock;
+
+ return &rstat_base_lock;
+}
+
+static raw_spinlock_t *ss_rstat_cpu_lock(struct cgroup_subsys *ss, int cpu)
+{
+ if (ss)
+ return per_cpu_ptr(ss->percpu_lock, cpu);
+
+ return per_cpu_ptr(&rstat_base_cpu_lock, cpu);
+}
+
/*
- * Helper functions for rstat per CPU lock (cgroup_rstat_cpu_lock).
+ * Helper functions for rstat per CPU locks.
*
* This makes it easier to diagnose locking issues and contention in
* production environments. The parameter @fast_path determine the
@@ -29,20 +45,23 @@ static struct css_rstat_cpu *css_rstat_cpu(
* operations without handling high-frequency fast-path "update" events.
*/
static __always_inline
-unsigned long _cgroup_rstat_cpu_lock(raw_spinlock_t *cpu_lock, int cpu,
- struct cgroup *cgrp, const bool fast_path)
+unsigned long _css_rstat_cpu_lock(struct cgroup_subsys_state *css, int cpu,
+ const bool fast_path)
{
+ struct cgroup *cgrp = css->cgroup;
+ raw_spinlock_t *cpu_lock;
unsigned long flags;
bool contended;
/*
- * The _irqsave() is needed because cgroup_rstat_lock is
- * spinlock_t which is a sleeping lock on PREEMPT_RT. Acquiring
- * this lock with the _irq() suffix only disables interrupts on
- * a non-PREEMPT_RT kernel. The raw_spinlock_t below disables
- * interrupts on both configurations. The _irqsave() ensures
- * that interrupts are always disabled and later restored.
+ * The _irqsave() is needed because the locks used for flushing are
+ * spinlock_t which is a sleeping lock on PREEMPT_RT. Acquiring this lock
+ * with the _irq() suffix only disables interrupts on a non-PREEMPT_RT
+ * kernel. The raw_spinlock_t below disables interrupts on both
+ * configurations. The _irqsave() ensures that interrupts are always
+ * disabled and later restored.
*/
+ cpu_lock = ss_rstat_cpu_lock(css->ss, cpu);
contended = !raw_spin_trylock_irqsave(cpu_lock, flags);
if (contended) {
if (fast_path)
@@ -62,15 +81,18 @@ unsigned long _cgroup_rstat_cpu_lock(raw_spinlock_t *cpu_lock, int cpu,
}
static __always_inline
-void _cgroup_rstat_cpu_unlock(raw_spinlock_t *cpu_lock, int cpu,
- struct cgroup *cgrp, unsigned long flags,
- const bool fast_path)
+void _css_rstat_cpu_unlock(struct cgroup_subsys_state *css, int cpu,
+ unsigned long flags, const bool fast_path)
{
+ struct cgroup *cgrp = css->cgroup;
+ raw_spinlock_t *cpu_lock;
+
if (fast_path)
trace_cgroup_rstat_cpu_unlock_fastpath(cgrp, cpu, false);
else
trace_cgroup_rstat_cpu_unlock(cgrp, cpu, false);
+ cpu_lock = ss_rstat_cpu_lock(css->ss, cpu);
raw_spin_unlock_irqrestore(cpu_lock, flags);
}
@@ -85,8 +107,6 @@ void _cgroup_rstat_cpu_unlock(raw_spinlock_t *cpu_lock, int cpu,
*/
void css_rstat_updated(struct cgroup_subsys_state *css, int cpu)
{
- struct cgroup *cgrp = css->cgroup;
- raw_spinlock_t *cpu_lock = per_cpu_ptr(&cgroup_rstat_cpu_lock, cpu);
unsigned long flags;
/*
@@ -100,7 +120,7 @@ void css_rstat_updated(struct cgroup_subsys_state *css, int cpu)
if (data_race(css_rstat_cpu(css, cpu)->updated_next))
return;
- flags = _cgroup_rstat_cpu_lock(cpu_lock, cpu, cgrp, true);
+ flags = _css_rstat_cpu_lock(css, cpu, true);
/* put @css and all ancestors on the corresponding updated lists */
while (true) {
@@ -128,7 +148,7 @@ void css_rstat_updated(struct cgroup_subsys_state *css, int cpu)
css = parent;
}
- _cgroup_rstat_cpu_unlock(cpu_lock, cpu, cgrp, flags, true);
+ _css_rstat_cpu_unlock(css, cpu, flags, true);
}
__bpf_kfunc void bpf_cgroup_rstat_updated(struct cgroup *cgrp, int cpu)
@@ -211,13 +231,11 @@ static struct cgroup_subsys_state *cgroup_rstat_push_children(
static struct cgroup_subsys_state *css_rstat_updated_list(
struct cgroup_subsys_state *root, int cpu)
{
- struct cgroup *cgrp = root->cgroup;
- raw_spinlock_t *cpu_lock = per_cpu_ptr(&cgroup_rstat_cpu_lock, cpu);
struct css_rstat_cpu *rstatc = css_rstat_cpu(root, cpu);
struct cgroup_subsys_state *head = NULL, *parent, *child;
unsigned long flags;
- flags = _cgroup_rstat_cpu_lock(cpu_lock, cpu, cgrp, false);
+ flags = _css_rstat_cpu_lock(root, cpu, false);
/* Return NULL if this subtree is not on-list */
if (!rstatc->updated_next)
@@ -254,7 +272,7 @@ static struct cgroup_subsys_state *css_rstat_updated_list(
if (child != root)
head = cgroup_rstat_push_children(head, child, cpu);
unlock_ret:
- _cgroup_rstat_cpu_unlock(cpu_lock, cpu, cgrp, flags, false);
+ _css_rstat_cpu_unlock(root, cpu, flags, false);
return head;
}
@@ -281,7 +299,7 @@ __weak noinline void bpf_rstat_flush(struct cgroup *cgrp,
__bpf_hook_end();
/*
- * Helper functions for locking cgroup_rstat_lock.
+ * Helper functions for locking.
*
* This makes it easier to diagnose locking issues and contention in
* production environments. The parameter @cpu_in_loop indicate lock
@@ -289,35 +307,44 @@ __bpf_hook_end();
* value -1 is used when obtaining the main lock else this is the CPU
* number processed last.
*/
-static inline void __cgroup_rstat_lock(struct cgroup *cgrp, int cpu_in_loop)
- __acquires(&cgroup_rstat_lock)
+static inline void __css_rstat_lock(struct cgroup_subsys_state *css,
+ int cpu_in_loop)
+ __acquires(lock)
{
+ struct cgroup *cgrp = css->cgroup;
+ spinlock_t *lock;
bool contended;
- contended = !spin_trylock_irq(&cgroup_rstat_lock);
+ lock = ss_rstat_lock(css->ss);
+ contended = !spin_trylock_irq(lock);
if (contended) {
trace_cgroup_rstat_lock_contended(cgrp, cpu_in_loop, contended);
- spin_lock_irq(&cgroup_rstat_lock);
+ spin_lock_irq(lock);
}
trace_cgroup_rstat_locked(cgrp, cpu_in_loop, contended);
}
-static inline void __cgroup_rstat_unlock(struct cgroup *cgrp, int cpu_in_loop)
- __releases(&cgroup_rstat_lock)
+static inline void __css_rstat_unlock(struct cgroup_subsys_state *css,
+ int cpu_in_loop)
+ __releases(lock)
{
+ struct cgroup *cgrp = css->cgroup;
+ spinlock_t *lock;
+
+ lock = ss_rstat_lock(css->ss);
trace_cgroup_rstat_unlock(cgrp, cpu_in_loop, false);
- spin_unlock_irq(&cgroup_rstat_lock);
+ spin_unlock_irq(lock);
}
-/* see css_rstat_flush() */
+/* see css_rstat_flush()
+ *
+ * it is required that callers have previously acquired a lock via
+ * __css_rstat_lock(css)
+ */
static void css_rstat_flush_locked(struct cgroup_subsys_state *css)
- __releases(&cgroup_rstat_lock) __acquires(&cgroup_rstat_lock)
{
- struct cgroup *cgrp = css->cgroup;
int cpu;
- lockdep_assert_held(&cgroup_rstat_lock);
-
for_each_possible_cpu(cpu) {
struct cgroup_subsys_state *pos;
@@ -332,11 +359,11 @@ static void css_rstat_flush_locked(struct cgroup_subsys_state *css)
}
/* play nice and yield if necessary */
- if (need_resched() || spin_needbreak(&cgroup_rstat_lock)) {
- __cgroup_rstat_unlock(cgrp, cpu);
+ if (need_resched() || spin_needbreak(ss_rstat_lock(css->ss))) {
+ __css_rstat_unlock(css, cpu);
if (!cond_resched())
cpu_relax();
- __cgroup_rstat_lock(cgrp, cpu);
+ __css_rstat_lock(css, cpu);
}
}
}
@@ -356,13 +383,10 @@ static void css_rstat_flush_locked(struct cgroup_subsys_state *css)
*/
void css_rstat_flush(struct cgroup_subsys_state *css)
{
- struct cgroup *cgrp = css->cgroup;
-
might_sleep();
-
- __cgroup_rstat_lock(cgrp, -1);
+ __css_rstat_lock(css, -1);
css_rstat_flush_locked(css);
- __cgroup_rstat_unlock(cgrp, -1);
+ __css_rstat_unlock(css, -1);
}
__bpf_kfunc void bpf_cgroup_rstat_flush(struct cgroup *cgrp)
@@ -381,10 +405,8 @@ __bpf_kfunc void bpf_cgroup_rstat_flush(struct cgroup *cgrp)
*/
void css_rstat_flush_hold(struct cgroup_subsys_state *css)
{
- struct cgroup *cgrp = css->cgroup;
-
might_sleep();
- __cgroup_rstat_lock(cgrp, -1);
+ __css_rstat_lock(css, -1);
css_rstat_flush_locked(css);
}
@@ -394,8 +416,7 @@ void css_rstat_flush_hold(struct cgroup_subsys_state *css)
*/
void css_rstat_flush_release(struct cgroup_subsys_state *css)
{
- struct cgroup *cgrp = css->cgroup;
- __cgroup_rstat_unlock(cgrp, -1);
+ __css_rstat_unlock(css, -1);
}
int css_rstat_init(struct cgroup_subsys_state *css)
@@ -439,12 +460,36 @@ void css_rstat_exit(struct cgroup_subsys_state *css)
css->rstat_cpu = NULL;
}
-void __init cgroup_rstat_boot(void)
+/**
+ * ss_rstat_init - subsystem-specific rstat initialization
+ * @ss: target subsystem
+ *
+ * If @ss is NULL, the static locks associated with the base stats
+ * are initialized. If @ss is non-NULL, the subsystem-specific locks
+ * are initialized.
+ */
+int __init ss_rstat_init(struct cgroup_subsys *ss)
{
int cpu;
+ if (!ss) {
+ spin_lock_init(&rstat_base_lock);
+
+ for_each_possible_cpu(cpu)
+ raw_spin_lock_init(per_cpu_ptr(&rstat_base_cpu_lock, cpu));
+
+ return 0;
+ }
+
+ spin_lock_init(&ss->lock);
+ ss->percpu_lock = alloc_percpu(raw_spinlock_t);
+ if (!ss->percpu_lock)
+ return -ENOMEM;
+
for_each_possible_cpu(cpu)
- raw_spin_lock_init(per_cpu_ptr(&cgroup_rstat_cpu_lock, cpu));
+ raw_spin_lock_init(per_cpu_ptr(ss->percpu_lock, cpu));
+
+ return 0;
}
/*
--
2.47.1
