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Commit f994cb43 authored by Rama Aparna Mallavarapu's avatar Rama Aparna Mallavarapu
Browse files

perf/core: Add support for PMUs that can be read from more than 1 CPU 



Some PMUs events can be read from more than the one CPU. So allow the
PMU driver to mark events as such. For these events, we don't need to
reject reads or make smp calls to the event's CPU (and cause
unnecessary overhead and wake ups).

When a PMU driver marks an event as such, care must be taken by the
driver to make sure they can handle the event being read/updated from
more than 1 CPU at the same time (Eg: due to an IRQ indicating event
counter overflow and another thread trying to read the latest values).

Good examples of such events would be events from caches shared across
CPUs.

Change-Id: I3dad97fc95849e26bd2bb3e418cdb4d47f2e335c
Signed-off-by: default avatarSaravana Kannan <skannan@codeaurora.org>
Signed-off-by: default avatarRama Aparna Mallavarapu <aparnam@codeaurora.org>
parent cab34f97

include/linux/perf_event.h

+1 −0
Original line number Diff line number Diff line
@@ -646,6 +646,7 @@ struct perf_event { 


	int				oncpu;

	int				cpu;

	cpumask_t			readable_on_cpus;



	struct list_head		owner_entry;

	struct task_struct		*owner;

kernel/events/core.c

+19 −10
Original line number Diff line number Diff line
@@ -3901,10 +3901,12 @@ struct perf_read_data { 
static int __perf_event_read_cpu(struct perf_event *event, int event_cpu)

{

	u16 local_pkg, event_pkg;



	if (event->group_caps & PERF_EV_CAP_READ_ACTIVE_PKG) {

	int local_cpu = smp_processor_id();



	if (cpumask_test_cpu(local_cpu, &event->readable_on_cpus))

		return local_cpu;



	if (event->group_caps & PERF_EV_CAP_READ_ACTIVE_PKG) {

		event_pkg = topology_physical_package_id(event_cpu);

		local_pkg = topology_physical_package_id(local_cpu);
@@ -3996,7 +3998,8 @@ int perf_event_read_local(struct perf_event *event, u64 *value, 
{

	unsigned long flags;

	int ret = 0;



	int local_cpu = smp_processor_id();

	bool readable = cpumask_test_cpu(local_cpu, &event->readable_on_cpus);

	/*

	 * Disabling interrupts avoids all counter scheduling (context

	 * switches, timer based rotation and IPIs).
@@ -4021,7 +4024,8 @@ int perf_event_read_local(struct perf_event *event, u64 *value, 


	/* If this is a per-CPU event, it must be for this CPU */

	if (!(event->attach_state & PERF_ATTACH_TASK) &&

	    event->cpu != smp_processor_id()) {

	    event->cpu != local_cpu &&

	    !readable) {

		ret = -EINVAL;

		goto out;

	}
@@ -4037,7 +4041,7 @@ int perf_event_read_local(struct perf_event *event, u64 *value, 
	 * or local to this CPU. Furthermore it means its ACTIVE (otherwise

	 * oncpu == -1).

	 */

	if (event->oncpu == smp_processor_id())

	if (event->oncpu == smp_processor_id() || readable)

		event->pmu->read(event);



	*value = local64_read(&event->count);
@@ -4062,11 +4066,13 @@ static int perf_event_read(struct perf_event *event, bool group) 
	enum perf_event_state state = READ_ONCE(event->state);

	int event_cpu, ret = 0;

	bool active_event_skip_read = false;

	bool readable;



	/*

	 * If event is enabled and currently active on a CPU, update the

	 * value in the event structure:

	 */

	preempt_disable();

again:

	if (state == PERF_EVENT_STATE_ACTIVE) {
@@ -4077,13 +4083,16 @@ static int perf_event_read(struct perf_event *event, bool group) 
		 * Matches the smp_wmb() from event_sched_in().

		 */

		smp_rmb();



		event_cpu = READ_ONCE(event->oncpu);

		if ((unsigned)event_cpu >= nr_cpu_ids)

		readable = cpumask_test_cpu(smp_processor_id(),

				    &event->readable_on_cpus);

		if ((unsigned int)event_cpu >= nr_cpu_ids) {

			preempt_enable();

			return 0;

		}

		if (cpu_isolated(event_cpu) ||

			(event->attr.exclude_idle &&

				per_cpu(is_idle, event_cpu)) ||

				per_cpu(is_idle, event_cpu) && !readable) ||

				per_cpu(is_hotplugging, event_cpu))

			active_event_skip_read = true;

	}
@@ -4095,7 +4104,6 @@ static int perf_event_read(struct perf_event *event, bool group) 
			.ret = 0,

		};



		preempt_disable();

		event_cpu = __perf_event_read_cpu(event, event_cpu);



		/*
@@ -4110,7 +4118,6 @@ static int perf_event_read(struct perf_event *event, bool group) 
		 */

		(void)smp_call_function_single(event_cpu,

				__perf_event_read, &data, 1);

		preempt_enable();

		ret = data.ret;

	} else if (state == PERF_EVENT_STATE_INACTIVE ||

			(active_event_skip_read &&
@@ -4139,6 +4146,8 @@ static int perf_event_read(struct perf_event *event, bool group) 
		raw_spin_unlock_irqrestore(&ctx->lock, flags);

	}



	preempt_enable();



	return ret;

}