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perf/core: Pull pmu::sched_task() into perf_event_context_sched_out()

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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>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200821195754.20159-2-kan.liang@linux.intel.com
This commit is contained in:
Kan Liang 2020-08-21 12:57:53 -07:00 committed by Peter Zijlstra
parent 556cccad38
commit 44fae179ce
2 changed files with 17 additions and 31 deletions
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1
include/linux/perf_event.h
View File

@ -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;

47
kernel/events/core.c
View File

@ -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 @@ unlock:
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);
@ -12867,7 +12855,6 @@ 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));
}
}