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Subject[PATCH V2 2/3] perf/core: Pull pmu::sched_task() into perf_event_context_sched_out()
Date
From: Kan Liang <kan.liang@linux.intel.com>

The pmu::sched_task() is a context switch callback. It passes the
cpuctx->task_ctx as a parameter to the lower code. To find the
cpuctx->task_ctx, the current code iterates a cpuctx list.
The same context will iterated in perf_event_context_sched_out() soon.
Share the cpuctx->task_ctx can avoid the unnecessary iteration of the
cpuctx list.

The pmu::sched_task() is also required for the optimization case for
equivalent contexts.

The task_ctx_sched_out() will eventually disable and reenable the PMU
when schedule out events. Add perf_pmu_disable() and perf_pmu_enable()
around task_ctx_sched_out() don't break anything.

Drop the cpuctx->ctx.lock for the pmu::sched_task(). The lock is for
per-CPU context, which is not necessary for the per-task context
schedule.

No one uses sched_cb_entry, perf_sched_cb_usages, sched_cb_list, and
perf_pmu_sched_task() any more.

Suggested-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Kan Liang <kan.liang@linux.intel.com>
---

New patch for V2

include/linux/perf_event.h | 1 -
kernel/events/core.c | 47 ++++++++++++++------------------------
2 files changed, 17 insertions(+), 31 deletions(-)

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 3737e653f47e..9357720df7de 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -872,7 +872,6 @@ struct perf_cpu_context {
struct list_head cgrp_cpuctx_entry;
#endif

- struct list_head sched_cb_entry;
int sched_cb_usage;

int online;
diff --git a/kernel/events/core.c b/kernel/events/core.c
index c785cbadbdb8..d0393d1970b7 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -382,7 +382,6 @@ static DEFINE_MUTEX(perf_sched_mutex);
static atomic_t perf_sched_count;

static DEFINE_PER_CPU(atomic_t, perf_cgroup_events);
-static DEFINE_PER_CPU(int, perf_sched_cb_usages);
static DEFINE_PER_CPU(struct pmu_event_list, pmu_sb_events);

static atomic_t nr_mmap_events __read_mostly;
@@ -3384,10 +3383,12 @@ static void perf_event_context_sched_out(struct task_struct *task, int ctxn,
struct perf_event_context *parent, *next_parent;
struct perf_cpu_context *cpuctx;
int do_switch = 1;
+ struct pmu *pmu;

if (likely(!ctx))
return;

+ pmu = ctx->pmu;
cpuctx = __get_cpu_context(ctx);
if (!cpuctx->task_ctx)
return;
@@ -3417,11 +3418,15 @@ static void perf_event_context_sched_out(struct task_struct *task, int ctxn,
raw_spin_lock(&ctx->lock);
raw_spin_lock_nested(&next_ctx->lock, SINGLE_DEPTH_NESTING);
if (context_equiv(ctx, next_ctx)) {
- struct pmu *pmu = ctx->pmu;

WRITE_ONCE(ctx->task, next);
WRITE_ONCE(next_ctx->task, task);

+ perf_pmu_disable(pmu);
+
+ if (cpuctx->sched_cb_usage && pmu->sched_task)
+ pmu->sched_task(ctx, false);
+
/*
* PMU specific parts of task perf context can require
* additional synchronization. As an example of such
@@ -3433,6 +3438,8 @@ static void perf_event_context_sched_out(struct task_struct *task, int ctxn,
else
swap(ctx->task_ctx_data, next_ctx->task_ctx_data);

+ perf_pmu_enable(pmu);
+
/*
* RCU_INIT_POINTER here is safe because we've not
* modified the ctx and the above modification of
@@ -3455,21 +3462,22 @@ static void perf_event_context_sched_out(struct task_struct *task, int ctxn,

if (do_switch) {
raw_spin_lock(&ctx->lock);
+ perf_pmu_disable(pmu);
+
+ if (cpuctx->sched_cb_usage && pmu->sched_task)
+ pmu->sched_task(ctx, false);
task_ctx_sched_out(cpuctx, ctx, EVENT_ALL);
+
+ perf_pmu_enable(pmu);
raw_spin_unlock(&ctx->lock);
}
}

-static DEFINE_PER_CPU(struct list_head, sched_cb_list);
-
void perf_sched_cb_dec(struct pmu *pmu)
{
struct perf_cpu_context *cpuctx = this_cpu_ptr(pmu->pmu_cpu_context);

- this_cpu_dec(perf_sched_cb_usages);
-
- if (!--cpuctx->sched_cb_usage)
- list_del(&cpuctx->sched_cb_entry);
+ --cpuctx->sched_cb_usage;
}


@@ -3477,10 +3485,7 @@ void perf_sched_cb_inc(struct pmu *pmu)
{
struct perf_cpu_context *cpuctx = this_cpu_ptr(pmu->pmu_cpu_context);

- if (!cpuctx->sched_cb_usage++)
- list_add(&cpuctx->sched_cb_entry, this_cpu_ptr(&sched_cb_list));
-
- this_cpu_inc(perf_sched_cb_usages);
+ cpuctx->sched_cb_usage++;
}

/*
@@ -3509,20 +3514,6 @@ static void __perf_pmu_sched_task(struct perf_cpu_context *cpuctx, bool sched_in
perf_ctx_unlock(cpuctx, cpuctx->task_ctx);
}

-static void perf_pmu_sched_task(struct task_struct *prev,
- struct task_struct *next,
- bool sched_in)
-{
- struct perf_cpu_context *cpuctx;
-
- if (prev == next)
- return;
-
- list_for_each_entry(cpuctx, this_cpu_ptr(&sched_cb_list), sched_cb_entry)
- __perf_pmu_sched_task(cpuctx, sched_in);
-
-}
-
static void perf_event_switch(struct task_struct *task,
struct task_struct *next_prev, bool sched_in);

@@ -3545,9 +3536,6 @@ void __perf_event_task_sched_out(struct task_struct *task,
{
int ctxn;

- if (__this_cpu_read(perf_sched_cb_usages))
- perf_pmu_sched_task(task, next, false);
-
if (atomic_read(&nr_switch_events))
perf_event_switch(task, next, false);

@@ -12850,7 +12838,6 @@ static void __init perf_event_init_all_cpus(void)
#ifdef CONFIG_CGROUP_PERF
INIT_LIST_HEAD(&per_cpu(cgrp_cpuctx_list, cpu));
#endif
- INIT_LIST_HEAD(&per_cpu(sched_cb_list, cpu));
}
}

--
2.17.1
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