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Date: Thu, 8 Apr 2021 16:13:20 +0200
From: Daniel Bristot de Oliveira <bristot@...hat.com>
To: Steven Rostedt <rostedt@...dmis.org>, linux-kernel@...r.kernel.org
Cc: bristot@...hat.com, kcarcia@...hat.com,
Jonathan Corbet <corbet@....net>,
Ingo Molnar <mingo@...hat.com>,
Peter Zijlstra <peterz@...radead.org>,
Thomas Gleixner <tglx@...utronix.de>,
Alexandre Chartre <alexandre.chartre@...cle.com>,
Clark Willaims <williams@...hat.com>,
John Kacur <jkacur@...hat.com>,
Juri Lelli <juri.lelli@...hat.com>, linux-doc@...r.kernel.org
Subject: [RFC PATCH 2/5] tracing/hwlat: Implement the mode config option
Provides the "mode" config to the hardware latency detector. hwlatd has
two different operation modes. 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. This is the current behavior.
The "none" sets the allowed cpumask for a single hwlatd thread at the
startup, but skips the round-robin, letting the scheduler handle the
migration.
In preparation to the per-cpu mode.
Cc: Jonathan Corbet <corbet@....net>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Alexandre Chartre <alexandre.chartre@...cle.com>
Cc: Clark Willaims <williams@...hat.com>
Cc: John Kacur <jkacur@...hat.com>
Cc: Juri Lelli <juri.lelli@...hat.com>
Cc: linux-doc@...r.kernel.org
Cc: linux-kernel@...r.kernel.org
Signed-off-by: Daniel Bristot de Oliveira <bristot@...hat.com>
---
Documentation/trace/hwlat_detector.rst | 21 +++-
kernel/trace/trace_hwlat.c | 157 +++++++++++++++++++++++--
2 files changed, 162 insertions(+), 16 deletions(-)
diff --git a/Documentation/trace/hwlat_detector.rst b/Documentation/trace/hwlat_detector.rst
index 86f973a7763c..f63fdd867598 100644
--- a/Documentation/trace/hwlat_detector.rst
+++ b/Documentation/trace/hwlat_detector.rst
@@ -76,10 +76,19 @@ in /sys/kernel/tracing:
- hwlat_detector/width - specified amount of time to spin within window (usecs)
- hwlat_detector/window - amount of time between (width) runs (usecs)
- hwlat_detector/cpus - the CPUs to move the hwlat thread across
+ - hwlat_detector/mode - the thread mode
+
+By default, the hwlat detector's kernel thread will migrate across each CPU
+specified in cpumask at the beginning of a new window, in a round-robin
+fashion. This behavior can be changed by changing the thread mode,
+the available options are:
+
+ - none: do not force migration
+ - round-robin: migrate across each CPU specified in cpus between each window
+
+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.
-The hwlat detector's kernel thread will migrate across each CPU specified in
-cpus list between each window. The hwlat detector will also obey the
-tracing_cpumask, so the thread will migrate on the set of cpus that is
-both on its cpus list and in the global tracing_cpumask file.
-To limit the migration, either modify cpumask, or modify the hwlat kernel
-thread (named [hwlatd]) CPU affinity directly, and the migration will stop.
diff --git a/kernel/trace/trace_hwlat.c b/kernel/trace/trace_hwlat.c
index deecb93f97f2..3818200c9e24 100644
--- a/kernel/trace/trace_hwlat.c
+++ b/kernel/trace/trace_hwlat.c
@@ -60,6 +60,15 @@ 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 */
+static struct dentry *hwlat_thread_mode; /* hwlat thread mode */
+
+enum {
+ MODE_NONE = 0,
+ MODE_ROUND_ROBIN,
+ MODE_MAX
+};
+
+static char *thread_mode_str[] = { "none", "round-robin" };
/* Save the previous tracing_thresh value */
static unsigned long save_tracing_thresh;
@@ -97,11 +106,16 @@ static struct hwlat_data {
u64 sample_window; /* total sampling window (on+off) */
u64 sample_width; /* active sampling portion of window */
+ int thread_mode; /* thread mode */
+
} hwlat_data = {
.sample_window = DEFAULT_SAMPLE_WINDOW,
.sample_width = DEFAULT_SAMPLE_WIDTH,
+ .thread_mode = MODE_ROUND_ROBIN
};
+static bool hwlat_busy;
+
static void trace_hwlat_sample(struct hwlat_sample *sample)
{
struct trace_array *tr = hwlat_trace;
@@ -337,7 +351,8 @@ static int kthread_fn(void *data)
while (!kthread_should_stop()) {
- move_to_next_cpu();
+ if (hwlat_data.thread_mode == MODE_ROUND_ROBIN)
+ move_to_next_cpu();
local_irq_disable();
get_sample();
@@ -375,6 +390,14 @@ static int start_kthread(struct trace_array *tr)
if (hwlat_kthread)
return 0;
+
+ kthread = kthread_create(kthread_fn, NULL, "hwlatd");
+ if (IS_ERR(kthread)) {
+ pr_err(BANNER "could not start sampling thread\n");
+ return -ENOMEM;
+ }
+
+
/* Just pick the first CPU on first iteration */
get_online_cpus();
/*
@@ -386,16 +409,14 @@ static int start_kthread(struct trace_array *tr)
*/
cpumask_and(current_mask, cpu_online_mask, current_mask);
put_online_cpus();
- next_cpu = cpumask_first(current_mask);
- kthread = kthread_create(kthread_fn, NULL, "hwlatd");
- if (IS_ERR(kthread)) {
- pr_err(BANNER "could not start sampling thread\n");
- return -ENOMEM;
+ if (hwlat_data.thread_mode == MODE_ROUND_ROBIN) {
+ next_cpu = cpumask_first(current_mask);
+ cpumask_clear(current_mask);
+ cpumask_set_cpu(next_cpu, current_mask);
+
}
- cpumask_clear(current_mask);
- cpumask_set_cpu(next_cpu, current_mask);
sched_setaffinity(kthread->pid, current_mask);
hwlat_kthread = kthread;
@@ -615,6 +636,109 @@ hwlat_window_write(struct file *filp, const char __user *ubuf,
return cnt;
}
+static void *s_mode_start(struct seq_file *s, loff_t *pos)
+{
+ int mode = *pos;
+
+ if (mode >= MODE_MAX)
+ return NULL;
+
+ return pos;
+}
+
+static void *s_mode_next(struct seq_file *s, void *v, loff_t *pos)
+{
+ int mode = ++(*pos);
+
+ if (mode >= MODE_MAX)
+ return NULL;
+
+ return pos;
+}
+
+static int s_mode_show(struct seq_file *s, void *v)
+{
+ loff_t *pos = v;
+ int mode = *pos;
+
+ if (mode == hwlat_data.thread_mode)
+ seq_printf(s, "[%s]", thread_mode_str[mode]);
+ else
+ seq_printf(s, "%s", thread_mode_str[mode]);
+
+ if (mode != MODE_MAX)
+ seq_puts(s, " ");
+
+ return 0;
+}
+
+static void s_mode_stop(struct seq_file *s, void *v)
+{
+ seq_puts(s, "\n");
+}
+
+static const struct seq_operations thread_mode_seq_ops = {
+ .start = s_mode_start,
+ .next = s_mode_next,
+ .show = s_mode_show,
+ .stop = s_mode_stop
+};
+
+static int hwlat_mode_open(struct inode *inode, struct file *file)
+{
+ return seq_open(file, &thread_mode_seq_ops);
+};
+
+/**
+ * hwlat_mode_write - Write function for "mode" entry
+ * @filp: The active open file structure
+ * @ubuf: The user buffer that contains the value to write
+ * @cnt: The maximum number of bytes to write to "file"
+ * @ppos: The current position in @file
+ *
+ * This function provides a write implementation for the "mode" interface
+ * to the hardware latency detector. hwlatd has different operation modes.
+ * 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.
+ */
+static ssize_t hwlat_mode_write(struct file *filp, const char __user *ubuf,
+ size_t cnt, loff_t *ppos)
+{
+ const char *mode;
+ char buf[64];
+ int ret;
+ int i;
+
+ if (hwlat_busy)
+ return -EBUSY;
+
+ if (cnt >= sizeof(buf))
+ return -EINVAL;
+
+ if (copy_from_user(buf, ubuf, cnt))
+ return -EFAULT;
+
+ buf[cnt] = 0;
+
+ mode = strstrip(buf);
+
+ ret = -EINVAL;
+
+ for (i = 0; i < MODE_MAX; i++) {
+ if (strcmp(mode, thread_mode_str[i]) == 0) {
+ hwlat_data.thread_mode = i;
+ ret = cnt;
+ }
+ }
+
+ *ppos += cnt;
+
+ return cnt;
+}
+
+
static const struct file_operations width_fops = {
.open = tracing_open_generic,
.read = hwlat_read,
@@ -634,6 +758,14 @@ static const struct file_operations cpus_fops = {
.llseek = generic_file_llseek,
};
+static const struct file_operations thread_mode_fops = {
+ .open = hwlat_mode_open,
+ .read = seq_read,
+ .llseek = seq_lseek,
+ .release = seq_release,
+ .write = hwlat_mode_write
+
+};
/**
* init_tracefs - A function to initialize the tracefs interface files
@@ -677,6 +809,13 @@ static int init_tracefs(void)
if (!hwlat_cpumask_dentry)
goto err;
+ hwlat_thread_mode = trace_create_file("mode", 0644,
+ top_dir,
+ NULL,
+ &thread_mode_fops);
+ if (!hwlat_thread_mode)
+ goto err;
+
return 0;
err:
@@ -698,8 +837,6 @@ static void hwlat_tracer_stop(struct trace_array *tr)
stop_kthread();
}
-static bool hwlat_busy;
-
static int hwlat_tracer_init(struct trace_array *tr)
{
/* Only allow one instance to enable this */
--
2.30.2
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