From 8fa826b7344d6752f5cfd72380d9fe7bd8c6b928 Mon Sep 17 00:00:00 2001 From: Daniel Bristot de Oliveira Date: Tue, 22 Jun 2021 16:42:20 +0200 Subject: [PATCH] trace/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. Link: https://lkml.kernel.org/r/f3b1271262aa030c680e26615c1b9b2d71e55e92.1624372313.git.bristot@redhat.com Cc: Phil Auld Cc: Sebastian Andrzej Siewior Cc: Kate Carcia Cc: Jonathan Corbet Cc: Ingo Molnar Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: Alexandre Chartre Cc: Clark Willaims Cc: John Kacur Cc: Juri Lelli Cc: Borislav Petkov Cc: "H. Peter Anvin" Cc: x86@kernel.org Cc: linux-doc@vger.kernel.org Cc: linux-kernel@vger.kernel.org Signed-off-by: Daniel Bristot de Oliveira Signed-off-by: Steven Rostedt (VMware) --- Documentation/trace/hwlat_detector.rst | 12 +- kernel/trace/trace_hwlat.c | 179 +++++++++++++++++++++++-- 2 files changed, 175 insertions(+), 16 deletions(-) diff --git a/Documentation/trace/hwlat_detector.rst b/Documentation/trace/hwlat_detector.rst index 5739349649c8..4d952df0586a 100644 --- a/Documentation/trace/hwlat_detector.rst +++ b/Documentation/trace/hwlat_detector.rst @@ -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] diff --git a/kernel/trace/trace_hwlat.c b/kernel/trace/trace_hwlat.c index 0a5635401125..43a436d85a01 100644 --- a/kernel/trace/trace_hwlat.c +++ b/kernel/trace/trace_hwlat.c @@ -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 */