perf: Optimize event scheduling locking
Currently we only hold one ctx->lock at a time, which results in us
flipping back and forth between cpuctx->ctx.lock and task_ctx->lock.
Avoid this and gain large atomic regions by holding both locks. We
nest the task lock inside the cpu lock, since with task scheduling we
might have to change task ctx while holding the cpu ctx lock.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/20110409192141.769881865@chello.nl
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/kernel/events/core.c b/kernel/events/core.c
index d665ac4..d243af9 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -200,6 +200,22 @@
return this_cpu_ptr(ctx->pmu->pmu_cpu_context);
}
+static void perf_ctx_lock(struct perf_cpu_context *cpuctx,
+ struct perf_event_context *ctx)
+{
+ raw_spin_lock(&cpuctx->ctx.lock);
+ if (ctx)
+ raw_spin_lock(&ctx->lock);
+}
+
+static void perf_ctx_unlock(struct perf_cpu_context *cpuctx,
+ struct perf_event_context *ctx)
+{
+ if (ctx)
+ raw_spin_unlock(&ctx->lock);
+ raw_spin_unlock(&cpuctx->ctx.lock);
+}
+
#ifdef CONFIG_CGROUP_PERF
/*
@@ -340,11 +356,8 @@
rcu_read_lock();
list_for_each_entry_rcu(pmu, &pmus, entry) {
-
cpuctx = this_cpu_ptr(pmu->pmu_cpu_context);
- perf_pmu_disable(cpuctx->ctx.pmu);
-
/*
* perf_cgroup_events says at least one
* context on this CPU has cgroup events.
@@ -353,6 +366,8 @@
* events for a context.
*/
if (cpuctx->ctx.nr_cgroups > 0) {
+ perf_ctx_lock(cpuctx, cpuctx->task_ctx);
+ perf_pmu_disable(cpuctx->ctx.pmu);
if (mode & PERF_CGROUP_SWOUT) {
cpu_ctx_sched_out(cpuctx, EVENT_ALL);
@@ -372,9 +387,9 @@
cpuctx->cgrp = perf_cgroup_from_task(task);
cpu_ctx_sched_in(cpuctx, EVENT_ALL, task);
}
+ perf_pmu_enable(cpuctx->ctx.pmu);
+ perf_ctx_unlock(cpuctx, cpuctx->task_ctx);
}
-
- perf_pmu_enable(cpuctx->ctx.pmu);
}
rcu_read_unlock();
@@ -1759,15 +1774,14 @@
{
struct perf_event *event;
- raw_spin_lock(&ctx->lock);
ctx->is_active = 0;
if (likely(!ctx->nr_events))
- goto out;
+ return;
+
update_context_time(ctx);
update_cgrp_time_from_cpuctx(cpuctx);
-
if (!ctx->nr_active)
- goto out;
+ return;
perf_pmu_disable(ctx->pmu);
if (event_type & EVENT_PINNED) {
@@ -1780,8 +1794,6 @@
group_sched_out(event, cpuctx, ctx);
}
perf_pmu_enable(ctx->pmu);
-out:
- raw_spin_unlock(&ctx->lock);
}
/*
@@ -1929,8 +1941,10 @@
rcu_read_unlock();
if (do_switch) {
+ raw_spin_lock(&ctx->lock);
ctx_sched_out(ctx, cpuctx, EVENT_ALL);
cpuctx->task_ctx = NULL;
+ raw_spin_unlock(&ctx->lock);
}
}
@@ -2056,10 +2070,9 @@
{
u64 now;
- raw_spin_lock(&ctx->lock);
ctx->is_active = 1;
if (likely(!ctx->nr_events))
- goto out;
+ return;
now = perf_clock();
ctx->timestamp = now;
@@ -2074,9 +2087,6 @@
/* Then walk through the lower prio flexible groups */
if (event_type & EVENT_FLEXIBLE)
ctx_flexible_sched_in(ctx, cpuctx);
-
-out:
- raw_spin_unlock(&ctx->lock);
}
static void cpu_ctx_sched_in(struct perf_cpu_context *cpuctx,
@@ -2110,6 +2120,7 @@
if (cpuctx->task_ctx == ctx)
return;
+ perf_ctx_lock(cpuctx, ctx);
perf_pmu_disable(ctx->pmu);
/*
* We want to keep the following priority order:
@@ -2124,12 +2135,14 @@
cpuctx->task_ctx = ctx;
+ perf_pmu_enable(ctx->pmu);
+ perf_ctx_unlock(cpuctx, ctx);
+
/*
* Since these rotations are per-cpu, we need to ensure the
* cpu-context we got scheduled on is actually rotating.
*/
perf_pmu_rotate_start(ctx->pmu);
- perf_pmu_enable(ctx->pmu);
}
/*
@@ -2269,7 +2282,6 @@
u64 interrupts, now;
s64 delta;
- raw_spin_lock(&ctx->lock);
list_for_each_entry_rcu(event, &ctx->event_list, event_entry) {
if (event->state != PERF_EVENT_STATE_ACTIVE)
continue;
@@ -2301,7 +2313,6 @@
if (delta > 0)
perf_adjust_period(event, period, delta);
}
- raw_spin_unlock(&ctx->lock);
}
/*
@@ -2309,16 +2320,12 @@
*/
static void rotate_ctx(struct perf_event_context *ctx)
{
- raw_spin_lock(&ctx->lock);
-
/*
* Rotate the first entry last of non-pinned groups. Rotation might be
* disabled by the inheritance code.
*/
if (!ctx->rotate_disable)
list_rotate_left(&ctx->flexible_groups);
-
- raw_spin_unlock(&ctx->lock);
}
/*
@@ -2345,6 +2352,7 @@
rotate = 1;
}
+ perf_ctx_lock(cpuctx, cpuctx->task_ctx);
perf_pmu_disable(cpuctx->ctx.pmu);
perf_ctx_adjust_freq(&cpuctx->ctx, interval);
if (ctx)
@@ -2370,6 +2378,7 @@
list_del_init(&cpuctx->rotation_list);
perf_pmu_enable(cpuctx->ctx.pmu);
+ perf_ctx_unlock(cpuctx, cpuctx->task_ctx);
}
void perf_event_task_tick(void)
@@ -2424,9 +2433,9 @@
* in.
*/
perf_cgroup_sched_out(current);
- task_ctx_sched_out(ctx, EVENT_ALL);
raw_spin_lock(&ctx->lock);
+ task_ctx_sched_out(ctx, EVENT_ALL);
list_for_each_entry(event, &ctx->pinned_groups, group_entry) {
ret = event_enable_on_exec(event, ctx);
@@ -5982,6 +5991,7 @@
}
static struct lock_class_key cpuctx_mutex;
+static struct lock_class_key cpuctx_lock;
int perf_pmu_register(struct pmu *pmu, char *name, int type)
{
@@ -6032,6 +6042,7 @@
cpuctx = per_cpu_ptr(pmu->pmu_cpu_context, cpu);
__perf_event_init_context(&cpuctx->ctx);
lockdep_set_class(&cpuctx->ctx.mutex, &cpuctx_mutex);
+ lockdep_set_class(&cpuctx->ctx.lock, &cpuctx_lock);
cpuctx->ctx.type = cpu_context;
cpuctx->ctx.pmu = pmu;
cpuctx->jiffies_interval = 1;
@@ -6776,7 +6787,6 @@
* our context.
*/
child_ctx = rcu_dereference_raw(child->perf_event_ctxp[ctxn]);
- task_ctx_sched_out(child_ctx, EVENT_ALL);
/*
* Take the context lock here so that if find_get_context is
@@ -6784,6 +6794,7 @@
* incremented the context's refcount before we do put_ctx below.
*/
raw_spin_lock(&child_ctx->lock);
+ task_ctx_sched_out(child_ctx, EVENT_ALL);
child->perf_event_ctxp[ctxn] = NULL;
/*
* If this context is a clone; unclone it so it can't get
