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 <[email protected]> Cc: Steven Rostedt <[email protected]> Cc: Ingo Molnar <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Thomas Gleixner <[email protected]> Cc: Alexandre Chartre <[email protected]> Cc: Clark Willaims <[email protected]> Cc: John Kacur <[email protected]> Cc: Juri Lelli <[email protected]> Cc: [email protected] Cc: [email protected] Signed-off-by: Daniel Bristot de Oliveira <[email protected]> --- 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
