tracing: Have hwlat trace migrate across tracing_cpumask CPUs (0330f7aa) · Commits · 戴 / test

Documentation/trace/hwlat_detector.txt

+6 −0

Original line number	Diff line number	Diff line
		@@ -69,5 +69,11 @@ in /sys/kernel/tracing:

		tracing_threshold - minimum latency value to be considered (usecs)
		tracing_max_latency - maximum hardware latency actually observed (usecs)
		tracing_cpumask - the CPUs to move the hwlat thread across
		hwlat_detector/width - specified amount of time to spin within window (usecs)
		hwlat_detector/window - amount of time between (width) runs (usecs)

		The hwlat detector's kernel thread will migrate across each CPU specified in
		tracing_cpumask between each window. To limit the migration, either modify
		tracing_cpumask, or modify the hwlat kernel thread (named [hwlatd]) CPU
		affinity directly, and the migration will stop.

kernel/trace/trace_hwlat.c

+55 −0

Original line number	Diff line number	Diff line
		@@ -42,6 +42,7 @@
		#include <linux/kthread.h>
		#include <linux/tracefs.h>
		#include <linux/uaccess.h>
		#include <linux/cpumask.h>
		#include <linux/delay.h>
		#include "trace.h"

		@@ -211,6 +212,57 @@ out:
		return ret;
		}

		static struct cpumask save_cpumask;
		static bool disable_migrate;

		static void move_to_next_cpu(void)
		{
		static struct cpumask *current_mask;
		int next_cpu;

		if (disable_migrate)
		return;

		/* Just pick the first CPU on first iteration */
		if (!current_mask) {
		current_mask = &save_cpumask;
		get_online_cpus();
		cpumask_and(current_mask, cpu_online_mask, tracing_buffer_mask);
		put_online_cpus();
		next_cpu = cpumask_first(current_mask);
		goto set_affinity;
		}

		/*
		* If for some reason the user modifies the CPU affinity
		* of this thread, than stop migrating for the duration
		* of the current test.
		*/
		if (!cpumask_equal(current_mask, &current->cpus_allowed))
		goto disable;

		get_online_cpus();
		cpumask_and(current_mask, cpu_online_mask, tracing_buffer_mask);
		next_cpu = cpumask_next(smp_processor_id(), current_mask);
		put_online_cpus();

		if (next_cpu >= nr_cpu_ids)
		next_cpu = cpumask_first(current_mask);

		set_affinity:
		if (next_cpu >= nr_cpu_ids) /* Shouldn't happen! */
		goto disable;

		cpumask_clear(current_mask);
		cpumask_set_cpu(next_cpu, current_mask);

		sched_setaffinity(0, current_mask);
		return;

		disable:
		disable_migrate = true;
		}

		/*
		* kthread_fn - The CPU time sampling/hardware latency detection kernel thread
		*
		@@ -230,6 +282,8 @@ static int kthread_fn(void *data)

		while (!kthread_should_stop()) {

		move_to_next_cpu();

		local_irq_disable();
		get_sample();
		local_irq_enable();
		@@ -473,6 +527,7 @@ static int hwlat_tracer_init(struct trace_array *tr)

		hwlat_trace = tr;

		disable_migrate = false;
		hwlat_data.count = 0;
		tr->max_latency = 0;
		save_tracing_thresh = tracing_thresh;

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