Implements the per-cpu mode in which a sampling thread is created for
each cpu in the "cpus" (and tracing_mask).
The per-cpu mode has the potention to speed up the hwlat detection by
running on multiple CPUs at the same time.
Cc: Jonathan Corbet <corbet@xxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Alexandre Chartre <alexandre.chartre@xxxxxxxxxx>
Cc: Clark Willaims <williams@xxxxxxxxxx>
Cc: John Kacur <jkacur@xxxxxxxxxx>
Cc: Juri Lelli <juri.lelli@xxxxxxxxxx>
Cc: linux-doc@xxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Signed-off-by: Daniel Bristot de Oliveira <bristot@xxxxxxxxxx>
---
Documentation/trace/hwlat_detector.rst | 6 +-
kernel/trace/trace_hwlat.c | 171 +++++++++++++++++++------
2 files changed, 137 insertions(+), 40 deletions(-)
diff --git a/Documentation/trace/hwlat_detector.rst b/Documentation/trace/hwlat_detector.rst
index f63fdd867598..7a6fab105b29 100644
--- a/Documentation/trace/hwlat_detector.rst
+++ b/Documentation/trace/hwlat_detector.rst
@@ -85,10 +85,12 @@ the available options are:
- none: do not force migration
- round-robin: migrate across each CPU specified in cpus between each window
+ - per-cpu: create a per-cpu thread for each cpu in cpus
By default, hwlat detector will also obey the tracing_cpumask, so the thread
will be placed only in the set of cpus that is both on the hwlat detector's
cpus and in the global tracing_cpumask file. The user can overwrite the
cpumask by setting it manually. Changing the hwlatd affinity externally,
-e.g., via taskset tool, will disable the round-robin migration.
-
+e.g., via taskset tool, will disable the round-robin migration. In the
+per-cpu mode, the per-cpu thread (hwlatd/CPU) will be pinned to its relative
+cpu, and its affinity cannot be changed.
diff --git a/kernel/trace/trace_hwlat.c b/kernel/trace/trace_hwlat.c
index 3818200c9e24..52968ea312df 100644
--- a/kernel/trace/trace_hwlat.c
+++ b/kernel/trace/trace_hwlat.c
@@ -34,7 +34,7 @@
* Copyright (C) 2008-2009 Jon Masters, Red Hat, Inc. <jcm@xxxxxxxxxx>
* Copyright (C) 2013-2016 Steven Rostedt, Red Hat, Inc. <srostedt@xxxxxxxxxx>
*
- * Includes useful feedback from Clark Williams <clark@xxxxxxxxxx>
+ * Includes useful feedback from Clark Williams <williams@xxxxxxxxxx>
*
*/
#include <linux/kthread.h>
@@ -54,9 +54,6 @@ static struct trace_array *hwlat_trace;
#define DEFAULT_SAMPLE_WIDTH 500000 /* 0.5s */
#define DEFAULT_LAT_THRESHOLD 10 /* 10us */
-/* sampling thread*/
-static struct task_struct *hwlat_kthread;
-
static struct dentry *hwlat_sample_width; /* sample width us */
static struct dentry *hwlat_sample_window; /* sample window us */
static struct dentry *hwlat_cpumask_dentry; /* hwlat cpus allowed */
@@ -65,19 +62,27 @@ static struct dentry *hwlat_thread_mode; /* hwlat thread mode */
enum {
MODE_NONE = 0,
MODE_ROUND_ROBIN,
+ MODE_PER_CPU,
MODE_MAX
};
-static char *thread_mode_str[] = { "none", "round-robin" };
+static char *thread_mode_str[] = { "none", "round-robin", "per-cpu" };
/* Save the previous tracing_thresh value */
static unsigned long save_tracing_thresh;
-/* NMI timestamp counters */
-static u64 nmi_ts_start;
-static u64 nmi_total_ts;
-static int nmi_count;
-static int nmi_cpu;
+/* runtime kthread data */
+struct hwlat_kthread_data {
+ struct task_struct *kthread;
+ /* NMI timestamp counters */
+ u64 nmi_ts_start;
+ u64 nmi_total_ts;
+ int nmi_count;
+ int nmi_cpu;
+};
+
+struct hwlat_kthread_data hwlat_single_cpu_data;
+DEFINE_PER_CPU(struct hwlat_kthread_data, hwlat_per_cpu_data);
/* Tells NMIs to call back to the hwlat tracer to record timestamps */
bool trace_hwlat_callback_enabled;
@@ -114,6 +119,14 @@ static struct hwlat_data {
.thread_mode = MODE_ROUND_ROBIN
};
+struct hwlat_kthread_data *get_cpu_data(void)
+{
+ if (hwlat_data.thread_mode == MODE_PER_CPU)
+ return this_cpu_ptr(&hwlat_per_cpu_data);
+ else
+ return &hwlat_single_cpu_data;
+}
+
static bool hwlat_busy;
static void trace_hwlat_sample(struct hwlat_sample *sample)
@@ -151,7 +164,9 @@ static void trace_hwlat_sample(struct hwlat_sample *sample)
void trace_hwlat_callback(bool enter)
{
- if (smp_processor_id() != nmi_cpu)
+ struct hwlat_kthread_data *kdata = get_cpu_data();
+
+ if (kdata->kthread)
return;
/*
@@ -160,13 +175,13 @@ void trace_hwlat_callback(bool enter)
*/
if (!IS_ENABLED(CONFIG_GENERIC_SCHED_CLOCK)) {
if (enter)
- nmi_ts_start = time_get();
+ kdata->nmi_ts_start = time_get();
else
- nmi_total_ts += time_get() - nmi_ts_start;
+ kdata->nmi_total_ts += time_get() - kdata->nmi_ts_start;
}
if (enter)
- nmi_count++;
+ kdata->nmi_count++;
}
/**
@@ -178,6 +193,7 @@ void trace_hwlat_callback(bool enter)
*/
static int get_sample(void)
{
+ struct hwlat_kthread_data *kdata = get_cpu_data();
struct trace_array *tr = hwlat_trace;
struct hwlat_sample s;
time_type start, t1, t2, last_t2;
@@ -190,9 +206,8 @@ static int get_sample(void)
do_div(thresh, NSEC_PER_USEC); /* modifies interval value */
- nmi_cpu = smp_processor_id();
- nmi_total_ts = 0;
- nmi_count = 0;
+ kdata->nmi_total_ts = 0;
+ kdata->nmi_count = 0;
/* Make sure NMIs see this first */
barrier();
@@ -262,15 +277,15 @@ static int get_sample(void)
ret = 1;
/* We read in microseconds */
- if (nmi_total_ts)
- do_div(nmi_total_ts, NSEC_PER_USEC);
+ if (kdata->nmi_total_ts)
+ do_div(kdata->nmi_total_ts, NSEC_PER_USEC);
hwlat_data.count++;
s.seqnum = hwlat_data.count;
s.duration = sample;
s.outer_duration = outer_sample;
- s.nmi_total_ts = nmi_total_ts;
- s.nmi_count = nmi_count;
+ s.nmi_total_ts = kdata->nmi_total_ts;
+ s.nmi_count = kdata->nmi_count;
s.count = count;
trace_hwlat_sample(&s);
@@ -376,23 +391,43 @@ static int kthread_fn(void *data)
}
/**
- * start_kthread - Kick off the hardware latency sampling/detector kthread
+ * stop_stop_kthread - Inform the hardware latency samping/detector kthread to stop
+ *
+ * This kicks the running hardware latency sampling/detector kernel thread and
+ * tells it to stop sampling now. Use this on unload and at system shutdown.
+ */
+static void stop_single_kthread(void)
+{
+ struct hwlat_kthread_data *kdata = get_cpu_data();
+ struct task_struct *kthread = kdata->kthread;
+
+ if (!kthread)
+
+ return;
+ kthread_stop(kthread);
+
+ kdata->kthread = NULL;
+}
+
+
+/**
+ * start_single_kthread - Kick off the hardware latency sampling/detector kthread
*
* This starts the kernel thread that will sit and sample the CPU timestamp
* counter (TSC or similar) and look for potential hardware latencies.
*/
-static int start_kthread(struct trace_array *tr)
+static int start_single_kthread(struct trace_array *tr)
{
+ struct hwlat_kthread_data *kdata = get_cpu_data();
struct cpumask *current_mask = &save_cpumask;
struct task_struct *kthread;
int next_cpu;
- if (hwlat_kthread)
+ if (kdata->kthread)
return 0;
-
kthread = kthread_create(kthread_fn, NULL, "hwlatd");
- if (IS_ERR(kthread)) {
+ if (IS_ERR(kdata->kthread)) {
pr_err(BANNER "could not start sampling thread\n");
return -ENOMEM;
}
@@ -419,24 +454,77 @@ static int start_kthread(struct trace_array *tr)
sched_setaffinity(kthread->pid, current_mask);
- hwlat_kthread = kthread;
+ kdata->kthread = kthread;
wake_up_process(kthread);
return 0;
}
/**
- * stop_kthread - Inform the hardware latency samping/detector kthread to stop
+ * stop_per_cpu_kthread - Inform the hardware latency samping/detector kthread to stop
*
- * This kicks the running hardware latency sampling/detector kernel thread and
+ * This kicks the running hardware latency sampling/detector kernel threads and
* tells it to stop sampling now. Use this on unload and at system shutdown.
*/
-static void stop_kthread(void)
+static void stop_per_cpu_kthreads(void)
{
- if (!hwlat_kthread)
- return;
- kthread_stop(hwlat_kthread);
- hwlat_kthread = NULL;
+ struct task_struct *kthread;
+ int cpu;
+
+ for_each_online_cpu(cpu) {
+ kthread = per_cpu(hwlat_per_cpu_data, cpu).kthread;
+ if (kthread)
+ kthread_stop(kthread);
+ }
+}
+
+/**
+ * start_per_cpu_kthread - Kick off the hardware latency sampling/detector kthreads
+ *
+ * This starts the kernel threads that will sit on potentially all cpus and
+ * sample the CPU timestamp counter (TSC or similar) and look for potential
+ * hardware latencies.
+ */
+static int start_per_cpu_kthreads(struct trace_array *tr)
+{
+ struct cpumask *current_mask = &save_cpumask;
+ struct cpumask *this_cpumask;
+ struct task_struct *kthread;
+ char comm[24];
+ int cpu;
+
+ if (!alloc_cpumask_var(&this_cpumask, GFP_KERNEL))
+ return -ENOMEM;
+
+ get_online_cpus();
+ /*
+ * Run only on CPUs in which trace and hwlat are allowed to run.
+ */
+ cpumask_and(current_mask, tr->tracing_cpumask, &hwlat_cpumask);
+ /*
+ * And the CPU is online.
+ */
+ cpumask_and(current_mask, cpu_online_mask, current_mask);
+ put_online_cpus();
+
+ for_each_online_cpu(cpu)
+ per_cpu(hwlat_per_cpu_data, cpu).kthread = NULL;
+
+ for_each_cpu(cpu, current_mask) {
+ snprintf(comm, 24, "hwlatd/%d", cpu);
+
+ kthread = kthread_create_on_cpu(kthread_fn, NULL, cpu, comm);
+ if (IS_ERR(kthread)) {
+ pr_err(BANNER "could not start sampling thread\n");
+ stop_per_cpu_kthreads();
+ return -ENOMEM;
+ }
+
+ per_cpu(hwlat_per_cpu_data, cpu).kthread = kthread;
+ wake_up_process(kthread);
+ }
+
+ return 0;
}
/*
@@ -701,7 +789,8 @@ static int hwlat_mode_open(struct inode *inode, struct file *file)
* The "none" sets the allowed cpumask for a single hwlatd thread at the
* startup and lets the scheduler handle the migration. The default mode is
* the "round-robin" one, in which a single hwlatd thread runs, migrating
- * among the allowed CPUs in a round-robin fashion.
+ * among the allowed CPUs in a round-robin fashion. The "per-cpu" mode
+ * creates one hwlatd thread per allowed CPU.
*/
static ssize_t hwlat_mode_write(struct file *filp, const char __user *ubuf,
size_t cnt, loff_t *ppos)
@@ -827,14 +916,20 @@ static void hwlat_tracer_start(struct trace_array *tr)
{
int err;
- err = start_kthread(tr);
+ if (hwlat_data.thread_mode == MODE_PER_CPU)
+ err = start_per_cpu_kthreads(tr);
+ else
+ err = start_single_kthread(tr);
if (err)
pr_err(BANNER "Cannot start hwlat kthread\n");
}
static void hwlat_tracer_stop(struct trace_array *tr)
{
- stop_kthread();
+ if (hwlat_data.thread_mode == MODE_PER_CPU)
+ stop_per_cpu_kthreads();
+ else
+ stop_single_kthread();
}
static int hwlat_tracer_init(struct trace_array *tr)
@@ -864,7 +959,7 @@ static int hwlat_tracer_init(struct trace_array *tr)
static void hwlat_tracer_reset(struct trace_array *tr)
{
- stop_kthread();
+ hwlat_tracer_stop(tr);
/* the tracing threshold is static between runs */
last_tracing_thresh = tracing_thresh;
--
2.30.2
