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trace/hwlat: Implement the mode config option

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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.

Link: https://lkml.kernel.org/r/f3b1271262aa030c680e26615c1b9b2d71e55e92.1624372313.git.bristot@redhat.com

Cc: Phil Auld <pauld@redhat.com>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Kate Carcia <kcarcia@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Alexandre Chartre <alexandre.chartre@oracle.com>
Cc: Clark Willaims <williams@redhat.com>
Cc: John Kacur <jkacur@redhat.com>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: x86@kernel.org
Cc: linux-doc@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Daniel Bristot de Oliveira <bristot@redhat.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
This commit is contained in:
Daniel Bristot de Oliveira 2021-06-22 16:42:20 +02:00 committed by Steven Rostedt (VMware)
parent bb1b24cf41
commit 8fa826b734
2 changed files with 175 additions and 16 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

12
Documentation/trace/hwlat_detector.rst
View File

@ -76,8 +76,12 @@ in /sys/kernel/tracing:
- 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)
- hwlat_detector/mode - the thread mode
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.
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 cpumask [default]

179
kernel/trace/trace_hwlat.c
View File

@ -59,6 +59,14 @@ 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_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;
@ -96,11 +104,16 @@ 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;
@ -328,7 +341,8 @@ 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();
@ -351,7 +365,7 @@ static int kthread_fn(void *data)
return 0;
}
/**
/*
* start_kthread - Kick off the hardware latency sampling/detector kthread
*
* This starts the kernel thread that will sit and sample the CPU timestamp
@ -366,11 +380,6 @@ static int start_kthread(struct trace_array *tr)
if (hwlat_kthread)
return 0;
/* Just pick the first CPU on first iteration */
get_online_cpus();
cpumask_and(current_mask, cpu_online_mask, tr->tracing_cpumask);
put_online_cpus();
next_cpu = cpumask_first(current_mask);
kthread = kthread_create(kthread_fn, NULL, "hwlatd");
if (IS_ERR(kthread)) {
@ -378,8 +387,19 @@ static int start_kthread(struct trace_array *tr)
return -ENOMEM;
}
cpumask_clear(current_mask);
cpumask_set_cpu(next_cpu, current_mask);
/* Just pick the first CPU on first iteration */
get_online_cpus();
cpumask_and(current_mask, cpu_online_mask, tr->tracing_cpumask);
put_online_cpus();
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);
}
sched_setaffinity(kthread->pid, current_mask);
hwlat_kthread = kthread;
@ -388,7 +408,7 @@ static int start_kthread(struct trace_array *tr)
return 0;
}
/**
/*
* stop_kthread - Inform the hardware latency sampling/detector kthread to stop
*
* This kicks the running hardware latency sampling/detector kernel thread and
@ -511,6 +531,129 @@ 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;
mutex_lock(&hwlat_data.lock);
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");
mutex_unlock(&hwlat_data.lock);
}
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);
};
static void hwlat_tracer_start(struct trace_array *tr);
static void hwlat_tracer_stop(struct trace_array *tr);
/**
* 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)
{
struct trace_array *tr = hwlat_trace;
const char *mode;
char buf[64];
int ret, i;
if (cnt >= sizeof(buf))
return -EINVAL;
if (copy_from_user(buf, ubuf, cnt))
return -EFAULT;
buf[cnt] = 0;
mode = strstrip(buf);
ret = -EINVAL;
/*
* trace_types_lock is taken to avoid concurrency on start/stop
* and hwlat_busy.
*/
mutex_lock(&trace_types_lock);
if (hwlat_busy)
hwlat_tracer_stop(tr);
mutex_lock(&hwlat_data.lock);
for (i = 0; i < MODE_MAX; i++) {
if (strcmp(mode, thread_mode_str[i]) == 0) {
hwlat_data.thread_mode = i;
ret = cnt;
}
}
mutex_unlock(&hwlat_data.lock);
if (hwlat_busy)
hwlat_tracer_start(tr);
mutex_unlock(&trace_types_lock);
*ppos += cnt;
return ret;
}
static const struct file_operations width_fops = {
.open = tracing_open_generic,
.read = hwlat_read,
@ -523,6 +666,13 @@ static const struct file_operations window_fops = {
.write = hwlat_window_write,
};
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
*
@ -558,6 +708,13 @@ static int init_tracefs(void)
if (!hwlat_sample_width)
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:
@ -579,8 +736,6 @@ 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 */