This is a note to let you know that I've just added the patch titled
perf: Optimize perf_cgroup_switch()
to the 6.5-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
perf-optimize-perf_cgroup_switch.patch
and it can be found in the queue-6.5 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit f0623a60d04027934779ec47852071c264f6506e
Author: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Date: Mon Oct 9 23:04:25 2023 +0200
perf: Optimize perf_cgroup_switch()
[ Upstream commit f06cc667f79909e9175460b167c277b7c64d3df0 ]
Namhyung reported that bd2756811766 ("perf: Rewrite core context handling")
regresses context switch overhead when perf-cgroup is in use together
with 'slow' PMUs like uncore.
Specifically, perf_cgroup_switch()'s perf_ctx_disable() /
ctx_sched_out() etc.. all iterate the full list of active PMUs for
that CPU, even if they don't have cgroup events.
Previously there was cgrp_cpuctx_list which linked the relevant PMUs
together, but that got lost in the rework. Instead of re-instruducing
a similar list, let the perf_event_pmu_context iteration skip those
that do not have cgroup events. This avoids growing multiple versions
of the perf_event_pmu_context iteration.
Measured performance (on a slightly different patch):
Before)
$ taskset -c 0 ./perf bench sched pipe -l 10000 -G AAA,BBB
# Running 'sched/pipe' benchmark:
# Executed 10000 pipe operations between two processes
Total time: 0.901 [sec]
90.128700 usecs/op
11095 ops/sec
After)
$ taskset -c 0 ./perf bench sched pipe -l 10000 -G AAA,BBB
# Running 'sched/pipe' benchmark:
# Executed 10000 pipe operations between two processes
Total time: 0.065 [sec]
6.560100 usecs/op
152436 ops/sec
Fixes: bd2756811766 ("perf: Rewrite core context handling")
Reported-by: Namhyung Kim <namhyung@xxxxxxxxxx>
Debugged-by: Namhyung Kim <namhyung@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Link: https://lkml.kernel.org/r/20231009210425.GC6307@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 227e9d45f61b6..e7afd0dd8a3d1 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -879,6 +879,7 @@ struct perf_event_pmu_context {
unsigned int embedded : 1;
unsigned int nr_events;
+ unsigned int nr_cgroups;
atomic_t refcount; /* event <-> epc */
struct rcu_head rcu_head;
diff --git a/kernel/events/core.c b/kernel/events/core.c
index f2f4d2b3beee0..e66398c9ffe05 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -375,6 +375,7 @@ enum event_type_t {
EVENT_TIME = 0x4,
/* see ctx_resched() for details */
EVENT_CPU = 0x8,
+ EVENT_CGROUP = 0x10,
EVENT_ALL = EVENT_FLEXIBLE | EVENT_PINNED,
};
@@ -684,20 +685,26 @@ do { \
___p; \
})
-static void perf_ctx_disable(struct perf_event_context *ctx)
+static void perf_ctx_disable(struct perf_event_context *ctx, bool cgroup)
{
struct perf_event_pmu_context *pmu_ctx;
- list_for_each_entry(pmu_ctx, &ctx->pmu_ctx_list, pmu_ctx_entry)
+ list_for_each_entry(pmu_ctx, &ctx->pmu_ctx_list, pmu_ctx_entry) {
+ if (cgroup && !pmu_ctx->nr_cgroups)
+ continue;
perf_pmu_disable(pmu_ctx->pmu);
+ }
}
-static void perf_ctx_enable(struct perf_event_context *ctx)
+static void perf_ctx_enable(struct perf_event_context *ctx, bool cgroup)
{
struct perf_event_pmu_context *pmu_ctx;
- list_for_each_entry(pmu_ctx, &ctx->pmu_ctx_list, pmu_ctx_entry)
+ list_for_each_entry(pmu_ctx, &ctx->pmu_ctx_list, pmu_ctx_entry) {
+ if (cgroup && !pmu_ctx->nr_cgroups)
+ continue;
perf_pmu_enable(pmu_ctx->pmu);
+ }
}
static void ctx_sched_out(struct perf_event_context *ctx, enum event_type_t event_type);
@@ -856,9 +863,9 @@ static void perf_cgroup_switch(struct task_struct *task)
return;
perf_ctx_lock(cpuctx, cpuctx->task_ctx);
- perf_ctx_disable(&cpuctx->ctx);
+ perf_ctx_disable(&cpuctx->ctx, true);
- ctx_sched_out(&cpuctx->ctx, EVENT_ALL);
+ ctx_sched_out(&cpuctx->ctx, EVENT_ALL|EVENT_CGROUP);
/*
* must not be done before ctxswout due
* to update_cgrp_time_from_cpuctx() in
@@ -870,9 +877,9 @@ static void perf_cgroup_switch(struct task_struct *task)
* perf_cgroup_set_timestamp() in ctx_sched_in()
* to not have to pass task around
*/
- ctx_sched_in(&cpuctx->ctx, EVENT_ALL);
+ ctx_sched_in(&cpuctx->ctx, EVENT_ALL|EVENT_CGROUP);
- perf_ctx_enable(&cpuctx->ctx);
+ perf_ctx_enable(&cpuctx->ctx, true);
perf_ctx_unlock(cpuctx, cpuctx->task_ctx);
}
@@ -965,6 +972,8 @@ perf_cgroup_event_enable(struct perf_event *event, struct perf_event_context *ct
if (!is_cgroup_event(event))
return;
+ event->pmu_ctx->nr_cgroups++;
+
/*
* Because cgroup events are always per-cpu events,
* @ctx == &cpuctx->ctx.
@@ -985,6 +994,8 @@ perf_cgroup_event_disable(struct perf_event *event, struct perf_event_context *c
if (!is_cgroup_event(event))
return;
+ event->pmu_ctx->nr_cgroups--;
+
/*
* Because cgroup events are always per-cpu events,
* @ctx == &cpuctx->ctx.
@@ -2679,9 +2690,9 @@ static void ctx_resched(struct perf_cpu_context *cpuctx,
event_type &= EVENT_ALL;
- perf_ctx_disable(&cpuctx->ctx);
+ perf_ctx_disable(&cpuctx->ctx, false);
if (task_ctx) {
- perf_ctx_disable(task_ctx);
+ perf_ctx_disable(task_ctx, false);
task_ctx_sched_out(task_ctx, event_type);
}
@@ -2699,9 +2710,9 @@ static void ctx_resched(struct perf_cpu_context *cpuctx,
perf_event_sched_in(cpuctx, task_ctx);
- perf_ctx_enable(&cpuctx->ctx);
+ perf_ctx_enable(&cpuctx->ctx, false);
if (task_ctx)
- perf_ctx_enable(task_ctx);
+ perf_ctx_enable(task_ctx, false);
}
void perf_pmu_resched(struct pmu *pmu)
@@ -3246,6 +3257,9 @@ ctx_sched_out(struct perf_event_context *ctx, enum event_type_t event_type)
struct perf_cpu_context *cpuctx = this_cpu_ptr(&perf_cpu_context);
struct perf_event_pmu_context *pmu_ctx;
int is_active = ctx->is_active;
+ bool cgroup = event_type & EVENT_CGROUP;
+
+ event_type &= ~EVENT_CGROUP;
lockdep_assert_held(&ctx->lock);
@@ -3292,8 +3306,11 @@ ctx_sched_out(struct perf_event_context *ctx, enum event_type_t event_type)
is_active ^= ctx->is_active; /* changed bits */
- list_for_each_entry(pmu_ctx, &ctx->pmu_ctx_list, pmu_ctx_entry)
+ list_for_each_entry(pmu_ctx, &ctx->pmu_ctx_list, pmu_ctx_entry) {
+ if (cgroup && !pmu_ctx->nr_cgroups)
+ continue;
__pmu_ctx_sched_out(pmu_ctx, is_active);
+ }
}
/*
@@ -3484,7 +3501,7 @@ perf_event_context_sched_out(struct task_struct *task, struct task_struct *next)
raw_spin_lock_nested(&next_ctx->lock, SINGLE_DEPTH_NESTING);
if (context_equiv(ctx, next_ctx)) {
- perf_ctx_disable(ctx);
+ perf_ctx_disable(ctx, false);
/* PMIs are disabled; ctx->nr_pending is stable. */
if (local_read(&ctx->nr_pending) ||
@@ -3504,7 +3521,7 @@ perf_event_context_sched_out(struct task_struct *task, struct task_struct *next)
perf_ctx_sched_task_cb(ctx, false);
perf_event_swap_task_ctx_data(ctx, next_ctx);
- perf_ctx_enable(ctx);
+ perf_ctx_enable(ctx, false);
/*
* RCU_INIT_POINTER here is safe because we've not
@@ -3528,13 +3545,13 @@ perf_event_context_sched_out(struct task_struct *task, struct task_struct *next)
if (do_switch) {
raw_spin_lock(&ctx->lock);
- perf_ctx_disable(ctx);
+ perf_ctx_disable(ctx, false);
inside_switch:
perf_ctx_sched_task_cb(ctx, false);
task_ctx_sched_out(ctx, EVENT_ALL);
- perf_ctx_enable(ctx);
+ perf_ctx_enable(ctx, false);
raw_spin_unlock(&ctx->lock);
}
}
@@ -3820,47 +3837,32 @@ static int merge_sched_in(struct perf_event *event, void *data)
return 0;
}
-static void ctx_pinned_sched_in(struct perf_event_context *ctx, struct pmu *pmu)
+static void pmu_groups_sched_in(struct perf_event_context *ctx,
+ struct perf_event_groups *groups,
+ struct pmu *pmu)
{
- struct perf_event_pmu_context *pmu_ctx;
int can_add_hw = 1;
-
- if (pmu) {
- visit_groups_merge(ctx, &ctx->pinned_groups,
- smp_processor_id(), pmu,
- merge_sched_in, &can_add_hw);
- } else {
- list_for_each_entry(pmu_ctx, &ctx->pmu_ctx_list, pmu_ctx_entry) {
- can_add_hw = 1;
- visit_groups_merge(ctx, &ctx->pinned_groups,
- smp_processor_id(), pmu_ctx->pmu,
- merge_sched_in, &can_add_hw);
- }
- }
+ visit_groups_merge(ctx, groups, smp_processor_id(), pmu,
+ merge_sched_in, &can_add_hw);
}
-static void ctx_flexible_sched_in(struct perf_event_context *ctx, struct pmu *pmu)
+static void ctx_groups_sched_in(struct perf_event_context *ctx,
+ struct perf_event_groups *groups,
+ bool cgroup)
{
struct perf_event_pmu_context *pmu_ctx;
- int can_add_hw = 1;
- if (pmu) {
- visit_groups_merge(ctx, &ctx->flexible_groups,
- smp_processor_id(), pmu,
- merge_sched_in, &can_add_hw);
- } else {
- list_for_each_entry(pmu_ctx, &ctx->pmu_ctx_list, pmu_ctx_entry) {
- can_add_hw = 1;
- visit_groups_merge(ctx, &ctx->flexible_groups,
- smp_processor_id(), pmu_ctx->pmu,
- merge_sched_in, &can_add_hw);
- }
+ list_for_each_entry(pmu_ctx, &ctx->pmu_ctx_list, pmu_ctx_entry) {
+ if (cgroup && !pmu_ctx->nr_cgroups)
+ continue;
+ pmu_groups_sched_in(ctx, groups, pmu_ctx->pmu);
}
}
-static void __pmu_ctx_sched_in(struct perf_event_context *ctx, struct pmu *pmu)
+static void __pmu_ctx_sched_in(struct perf_event_context *ctx,
+ struct pmu *pmu)
{
- ctx_flexible_sched_in(ctx, pmu);
+ pmu_groups_sched_in(ctx, &ctx->flexible_groups, pmu);
}
static void
@@ -3868,6 +3870,9 @@ ctx_sched_in(struct perf_event_context *ctx, enum event_type_t event_type)
{
struct perf_cpu_context *cpuctx = this_cpu_ptr(&perf_cpu_context);
int is_active = ctx->is_active;
+ bool cgroup = event_type & EVENT_CGROUP;
+
+ event_type &= ~EVENT_CGROUP;
lockdep_assert_held(&ctx->lock);
@@ -3900,11 +3905,11 @@ ctx_sched_in(struct perf_event_context *ctx, enum event_type_t event_type)
* in order to give them the best chance of going on.
*/
if (is_active & EVENT_PINNED)
- ctx_pinned_sched_in(ctx, NULL);
+ ctx_groups_sched_in(ctx, &ctx->pinned_groups, cgroup);
/* Then walk through the lower prio flexible groups */
if (is_active & EVENT_FLEXIBLE)
- ctx_flexible_sched_in(ctx, NULL);
+ ctx_groups_sched_in(ctx, &ctx->flexible_groups, cgroup);
}
static void perf_event_context_sched_in(struct task_struct *task)
@@ -3919,11 +3924,11 @@ static void perf_event_context_sched_in(struct task_struct *task)
if (cpuctx->task_ctx == ctx) {
perf_ctx_lock(cpuctx, ctx);
- perf_ctx_disable(ctx);
+ perf_ctx_disable(ctx, false);
perf_ctx_sched_task_cb(ctx, true);
- perf_ctx_enable(ctx);
+ perf_ctx_enable(ctx, false);
perf_ctx_unlock(cpuctx, ctx);
goto rcu_unlock;
}
@@ -3936,7 +3941,7 @@ static void perf_event_context_sched_in(struct task_struct *task)
if (!ctx->nr_events)
goto unlock;
- perf_ctx_disable(ctx);
+ perf_ctx_disable(ctx, false);
/*
* We want to keep the following priority order:
* cpu pinned (that don't need to move), task pinned,
@@ -3946,7 +3951,7 @@ static void perf_event_context_sched_in(struct task_struct *task)
* events, no need to flip the cpuctx's events around.
*/
if (!RB_EMPTY_ROOT(&ctx->pinned_groups.tree)) {
- perf_ctx_disable(&cpuctx->ctx);
+ perf_ctx_disable(&cpuctx->ctx, false);
ctx_sched_out(&cpuctx->ctx, EVENT_FLEXIBLE);
}
@@ -3955,9 +3960,9 @@ static void perf_event_context_sched_in(struct task_struct *task)
perf_ctx_sched_task_cb(cpuctx->task_ctx, true);
if (!RB_EMPTY_ROOT(&ctx->pinned_groups.tree))
- perf_ctx_enable(&cpuctx->ctx);
+ perf_ctx_enable(&cpuctx->ctx, false);
- perf_ctx_enable(ctx);
+ perf_ctx_enable(ctx, false);
unlock:
perf_ctx_unlock(cpuctx, ctx);
