From 44fae179ce73a26733d9e2d346da4e1a1cb94647 Mon Sep 17 00:00:00 2001 From: Kan Liang Date: Fri, 21 Aug 2020 12:57:53 -0700 Subject: [PATCH] perf/core: Pull pmu::sched_task() into perf_event_context_sched_out() 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) Signed-off-by: Kan Liang Signed-off-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/20200821195754.20159-2-kan.liang@linux.intel.com --- 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 46a3974eb4fe..0c19d279b97f 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 3f5fec4dcf01..45edb85344a1 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); @@ -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)); } }