perf/core: Optimize perf_pmu_sched_task() (e48c1788) · Commits · 戴 / test

For perf record -b, which requires the pmu::sched_task callback the current code is rather expensive: 7.68% sched-pipe [kernel.vmlinux] [k] perf_pmu_sched_task 5.95% sched-pipe [kernel.vmlinux] [k] __switch_to 5.20% sched-pipe [kernel.vmlinux] [k] __intel_pmu_disable_all 3.95% sched-pipe perf [.] worker_thread The problem is that it will iterate all registered PMUs, most of which will not have anything to do. Avoid this by keeping an explicit list of PMUs that have requested the callback. The perf_sched_cb_{inc,dec}() functions already takes the required pmu argument, and now that these functions are no longer called from NMI context we can use them to manage a list. With this patch applied the function doesn't show up in the top 4 anymore (it dropped to 18th place). 6.67% sched-pipe [kernel.vmlinux] [k] __switch_to 6.18% sched-pipe [kernel.vmlinux] [k] __intel_pmu_disable_all 3.92% sched-pipe [kernel.vmlinux] [k] switch_mm_irqs_off 3.71% sched-pipe perf [.] worker_thread Signed-off-by:

Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com> Cc: Arnaldo Carvalho de Melo <acme@redhat.com> Cc: Jiri Olsa <jolsa@redhat.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Stephane Eranian <eranian@google.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Vince Weaver <vincent.weaver@maine.edu> Cc: linux-kernel@vger.kernel.org Signed-off-by:

Ingo Molnar <mingo@kernel.org>

include/linux/perf_event.h

+3 −0

Original line number	Diff line number	Diff line
		@@ -774,6 +774,9 @@ struct perf_cpu_context {
		#ifdef CONFIG_CGROUP_PERF
		struct perf_cgroup *cgrp;
		#endif

		struct list_head sched_cb_entry;
		int sched_cb_usage;
		};

		struct perf_output_handle {

kernel/events/core.c

+24 −19

Original line number	Diff line number	Diff line
		@@ -2805,13 +2805,26 @@ unlock:
		}
		}

		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);
		}


		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);
		}

		@@ -2829,36 +2842,26 @@ static void perf_pmu_sched_task(struct task_struct *prev,
		{
		struct perf_cpu_context *cpuctx;
		struct pmu *pmu;
		unsigned long flags;

		if (prev == next)
		return;

		local_irq_save(flags);
		list_for_each_entry(cpuctx, this_cpu_ptr(&sched_cb_list), sched_cb_entry) {
		pmu = cpuctx->unique_pmu; /* software PMUs will not have sched_task */

		rcu_read_lock();

		list_for_each_entry_rcu(pmu, &pmus, entry) {
		if (pmu->sched_task) {
		cpuctx = this_cpu_ptr(pmu->pmu_cpu_context);
		if (WARN_ON_ONCE(!pmu->sched_task))
		continue;

		perf_ctx_lock(cpuctx, cpuctx->task_ctx);

		perf_pmu_disable(pmu);

		pmu->sched_task(cpuctx->task_ctx, sched_in);

		perf_pmu_enable(pmu);

		perf_ctx_unlock(cpuctx, cpuctx->task_ctx);
		}
		}

		rcu_read_unlock();

		local_irq_restore(flags);
		}

		static void perf_event_switch(struct task_struct *task,
		struct task_struct *next_prev, bool sched_in);

		@@ -10393,6 +10396,8 @@ static void __init perf_event_init_all_cpus(void)

		INIT_LIST_HEAD(&per_cpu(pmu_sb_events.list, cpu));
		raw_spin_lock_init(&per_cpu(pmu_sb_events.lock, cpu));

		INIT_LIST_HEAD(&per_cpu(sched_cb_list, cpu));
		}
		}

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