--- /dev/null
+/*
+ * trace_hwlatdetect.c - A simple Hardware Latency detector.
+ *
+ * Use this tracer to detect large system latencies induced by the behavior of
+ * certain underlying system hardware or firmware, independent of Linux itself.
+ * The code was developed originally to detect the presence of SMIs on Intel
+ * and AMD systems, although there is no dependency upon x86 herein.
+ *
+ * The classical example usage of this tracer is in detecting the presence of
+ * SMIs or System Management Interrupts on Intel and AMD systems. An SMI is a
+ * somewhat special form of hardware interrupt spawned from earlier CPU debug
+ * modes in which the (BIOS/EFI/etc.) firmware arranges for the South Bridge
+ * LPC (or other device) to generate a special interrupt under certain
+ * circumstances, for example, upon expiration of a special SMI timer device,
+ * due to certain external thermal readings, on certain I/O address accesses,
+ * and other situations. An SMI hits a special CPU pin, triggers a special
+ * SMI mode (complete with special memory map), and the OS is unaware.
+ *
+ * Although certain hardware-inducing latencies are necessary (for example,
+ * a modern system often requires an SMI handler for correct thermal control
+ * and remote management) they can wreak havoc upon any OS-level performance
+ * guarantees toward low-latency, especially when the OS is not even made
+ * aware of the presence of these interrupts. For this reason, we need a
+ * somewhat brute force mechanism to detect these interrupts. In this case,
+ * we do it by hogging all of the CPU(s) for configurable timer intervals,
+ * sampling the built-in CPU timer, looking for discontiguous readings.
+ *
+ * WARNING: This implementation necessarily introduces latencies. Therefore,
+ * you should NEVER use this tracer while running in a production
+ * environment requiring any kind of low-latency performance
+ * guarantee(s).
+ *
+ * Copyright (C) 2008-2009 Jon Masters, Red Hat, Inc. <jcm@redhat.com>
+ * Copyright (C) 2013-2016 Steven Rostedt, Red Hat, Inc. <srostedt@redhat.com>
+ *
+ * Includes useful feedback from Clark Williams <clark@redhat.com>
+ *
+ * This file is licensed under the terms of the GNU General Public
+ * License version 2. This program is licensed "as is" without any
+ * warranty of any kind, whether express or implied.
+ */
+#include <linux/kthread.h>
+#include <linux/tracefs.h>
+#include <linux/uaccess.h>
+#include <linux/delay.h>
+#include "trace.h"
+
+static struct trace_array *hwlat_trace;
+
+#define U64STR_SIZE 22 /* 20 digits max */
+
+#define BANNER "hwlat_detector: "
+#define DEFAULT_SAMPLE_WINDOW 1000000 /* 1s */
+#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 */
+
+/* Save the previous tracing_thresh value */
+static unsigned long save_tracing_thresh;
+
+/* If the user changed threshold, remember it */
+static u64 last_tracing_thresh = DEFAULT_LAT_THRESHOLD * NSEC_PER_USEC;
+
+/* Individual latency samples are stored here when detected. */
+struct hwlat_sample {
+ u64 seqnum; /* unique sequence */
+ u64 duration; /* delta */
+ u64 outer_duration; /* delta (outer loop) */
+ struct timespec timestamp; /* wall time */
+};
+
+/* keep the global state somewhere. */
+static struct hwlat_data {
+
+ struct mutex lock; /* protect changes */
+
+ u64 count; /* total since reset */
+
+ u64 sample_window; /* total sampling window (on+off) */
+ u64 sample_width; /* active sampling portion of window */
+
+} hwlat_data = {
+ .sample_window = DEFAULT_SAMPLE_WINDOW,
+ .sample_width = DEFAULT_SAMPLE_WIDTH,
+};
+
+static void trace_hwlat_sample(struct hwlat_sample *sample)
+{
+ struct trace_array *tr = hwlat_trace;
+ struct trace_event_call *call = &event_hwlat;
+ struct ring_buffer *buffer = tr->trace_buffer.buffer;
+ struct ring_buffer_event *event;
+ struct hwlat_entry *entry;
+ unsigned long flags;
+ int pc;
+
+ pc = preempt_count();
+ local_save_flags(flags);
+
+ event = trace_buffer_lock_reserve(buffer, TRACE_HWLAT, sizeof(*entry),
+ flags, pc);
+ if (!event)
+ return;
+ entry = ring_buffer_event_data(event);
+ entry->seqnum = sample->seqnum;
+ entry->duration = sample->duration;
+ entry->outer_duration = sample->outer_duration;
+ entry->timestamp = sample->timestamp;
+
+ if (!call_filter_check_discard(call, entry, buffer, event))
+ __buffer_unlock_commit(buffer, event);
+}
+
+/* Macros to encapsulate the time capturing infrastructure */
+#define time_type u64
+#define time_get() trace_clock_local()
+#define time_to_us(x) div_u64(x, 1000)
+#define time_sub(a, b) ((a) - (b))
+#define init_time(a, b) (a = b)
+#define time_u64(a) a
+
+/**
+ * get_sample - sample the CPU TSC and look for likely hardware latencies
+ *
+ * Used to repeatedly capture the CPU TSC (or similar), looking for potential
+ * hardware-induced latency. Called with interrupts disabled and with
+ * hwlat_data.lock held.
+ */
+static int get_sample(void)
+{
+ struct trace_array *tr = hwlat_trace;
+ time_type start, t1, t2, last_t2;
+ s64 diff, total, last_total = 0;
+ u64 sample = 0;
+ u64 thresh = tracing_thresh;
+ u64 outer_sample = 0;
+ int ret = -1;
+
+ do_div(thresh, NSEC_PER_USEC); /* modifies interval value */
+
+ init_time(last_t2, 0);
+ start = time_get(); /* start timestamp */
+
+ do {
+
+ t1 = time_get(); /* we'll look for a discontinuity */
+ t2 = time_get();
+
+ if (time_u64(last_t2)) {
+ /* Check the delta from outer loop (t2 to next t1) */
+ diff = time_to_us(time_sub(t1, last_t2));
+ /* This shouldn't happen */
+ if (diff < 0) {
+ pr_err(BANNER "time running backwards\n");
+ goto out;
+ }
+ if (diff > outer_sample)
+ outer_sample = diff;
+ }
+ last_t2 = t2;
+
+ total = time_to_us(time_sub(t2, start)); /* sample width */
+
+ /* Check for possible overflows */
+ if (total < last_total) {
+ pr_err("Time total overflowed\n");
+ break;
+ }
+ last_total = total;
+
+ /* This checks the inner loop (t1 to t2) */
+ diff = time_to_us(time_sub(t2, t1)); /* current diff */
+
+ /* This shouldn't happen */
+ if (diff < 0) {
+ pr_err(BANNER "time running backwards\n");
+ goto out;
+ }
+
+ if (diff > sample)
+ sample = diff; /* only want highest value */
+
+ } while (total <= hwlat_data.sample_width);
+
+ ret = 0;
+
+ /* If we exceed the threshold value, we have found a hardware latency */
+ if (sample > thresh || outer_sample > thresh) {
+ struct hwlat_sample s;
+
+ ret = 1;
+
+ hwlat_data.count++;
+ s.seqnum = hwlat_data.count;
+ s.duration = sample;
+ s.outer_duration = outer_sample;
+ s.timestamp = CURRENT_TIME;
+ trace_hwlat_sample(&s);
+
+ /* Keep a running maximum ever recorded hardware latency */
+ if (sample > tr->max_latency)
+ tr->max_latency = sample;
+ }
+
+out:
+ return ret;
+}
+
+/*
+ * kthread_fn - The CPU time sampling/hardware latency detection kernel thread
+ *
+ * Used to periodically sample the CPU TSC via a call to get_sample. We
+ * disable interrupts, which does (intentionally) introduce latency since we
+ * need to ensure nothing else might be running (and thus preempting).
+ * Obviously this should never be used in production environments.
+ *
+ * Currently this runs on which ever CPU it was scheduled on, but most
+ * real-world hardware latency situations occur across several CPUs,
+ * but we might later generalize this if we find there are any actualy
+ * systems with alternate SMI delivery or other hardware latencies.
+ */
+static int kthread_fn(void *data)
+{
+ u64 interval;
+
+ while (!kthread_should_stop()) {
+
+ local_irq_disable();
+ get_sample();
+ local_irq_enable();
+
+ mutex_lock(&hwlat_data.lock);
+ interval = hwlat_data.sample_window - hwlat_data.sample_width;
+ mutex_unlock(&hwlat_data.lock);
+
+ do_div(interval, USEC_PER_MSEC); /* modifies interval value */
+
+ /* Always sleep for at least 1ms */
+ if (interval < 1)
+ interval = 1;
+
+ if (msleep_interruptible(interval))
+ break;
+ }
+
+ 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
+ * counter (TSC or similar) and look for potential hardware latencies.
+ */
+static int start_kthread(struct trace_array *tr)
+{
+ struct task_struct *kthread;
+
+ kthread = kthread_create(kthread_fn, NULL, "hwlatd");
+ if (IS_ERR(kthread)) {
+ pr_err(BANNER "could not start sampling thread\n");
+ return -ENOMEM;
+ }
+ hwlat_kthread = kthread;
+ wake_up_process(kthread);
+
+ return 0;
+}
+
+/**
+ * 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_kthread(void)
+{
+ if (!hwlat_kthread)
+ return;
+ kthread_stop(hwlat_kthread);
+ hwlat_kthread = NULL;
+}
+
+/*
+ * hwlat_read - Wrapper read function for reading both window and width
+ * @filp: The active open file structure
+ * @ubuf: The userspace provided buffer to read value into
+ * @cnt: The maximum number of bytes to read
+ * @ppos: The current "file" position
+ *
+ * This function provides a generic read implementation for the global state
+ * "hwlat_data" structure filesystem entries.
+ */
+static ssize_t hwlat_read(struct file *filp, char __user *ubuf,
+ size_t cnt, loff_t *ppos)
+{
+ char buf[U64STR_SIZE];
+ u64 *entry = filp->private_data;
+ u64 val;
+ int len;
+
+ if (!entry)
+ return -EFAULT;
+
+ if (cnt > sizeof(buf))
+ cnt = sizeof(buf);
+
+ val = *entry;
+
+ len = snprintf(buf, sizeof(buf), "%llu\n", val);
+
+ return simple_read_from_buffer(ubuf, cnt, ppos, buf, len);
+}
+
+/**
+ * hwlat_width_write - Write function for "width" 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 "width" interface
+ * to the hardware latency detector. It can be used to configure
+ * for how many us of the total window us we will actively sample for any
+ * hardware-induced latency periods. Obviously, it is not possible to
+ * sample constantly and have the system respond to a sample reader, or,
+ * worse, without having the system appear to have gone out to lunch. It
+ * is enforced that width is less that the total window size.
+ */
+static ssize_t
+hwlat_width_write(struct file *filp, const char __user *ubuf,
+ size_t cnt, loff_t *ppos)
+{
+ u64 val;
+ int err;
+
+ err = kstrtoull_from_user(ubuf, cnt, 10, &val);
+ if (err)
+ return err;
+
+ mutex_lock(&hwlat_data.lock);
+ if (val < hwlat_data.sample_window)
+ hwlat_data.sample_width = val;
+ else
+ err = -EINVAL;
+ mutex_unlock(&hwlat_data.lock);
+
+ if (err)
+ return err;
+
+ return cnt;
+}
+
+/**
+ * hwlat_window_write - Write function for "window" 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 "window" interface
+ * to the hardware latency detetector. The window is the total time
+ * in us that will be considered one sample period. Conceptually, windows
+ * occur back-to-back and contain a sample width period during which
+ * actual sampling occurs. Can be used to write a new total window size. It
+ * is enfoced that any value written must be greater than the sample width
+ * size, or an error results.
+ */
+static ssize_t
+hwlat_window_write(struct file *filp, const char __user *ubuf,
+ size_t cnt, loff_t *ppos)
+{
+ u64 val;
+ int err;
+
+ err = kstrtoull_from_user(ubuf, cnt, 10, &val);
+ if (err)
+ return err;
+
+ mutex_lock(&hwlat_data.lock);
+ if (hwlat_data.sample_width < val)
+ hwlat_data.sample_window = val;
+ else
+ err = -EINVAL;
+ mutex_unlock(&hwlat_data.lock);
+
+ if (err)
+ return err;
+
+ return cnt;
+}
+
+static const struct file_operations width_fops = {
+ .open = tracing_open_generic,
+ .read = hwlat_read,
+ .write = hwlat_width_write,
+};
+
+static const struct file_operations window_fops = {
+ .open = tracing_open_generic,
+ .read = hwlat_read,
+ .write = hwlat_window_write,
+};
+
+/**
+ * init_tracefs - A function to initialize the tracefs interface files
+ *
+ * This function creates entries in tracefs for "hwlat_detector".
+ * It creates the hwlat_detector directory in the tracing directory,
+ * and within that directory is the count, width and window files to
+ * change and view those values.
+ */
+static int init_tracefs(void)
+{
+ struct dentry *d_tracer;
+ struct dentry *top_dir;
+
+ d_tracer = tracing_init_dentry();
+ if (IS_ERR(d_tracer))
+ return -ENOMEM;
+
+ top_dir = tracefs_create_dir("hwlat_detector", d_tracer);
+ if (!top_dir)
+ return -ENOMEM;
+
+ hwlat_sample_window = tracefs_create_file("window", 0640,
+ top_dir,
+ &hwlat_data.sample_window,
+ &window_fops);
+ if (!hwlat_sample_window)
+ goto err;
+
+ hwlat_sample_width = tracefs_create_file("width", 0644,
+ top_dir,
+ &hwlat_data.sample_width,
+ &width_fops);
+ if (!hwlat_sample_width)
+ goto err;
+
+ return 0;
+
+ err:
+ tracefs_remove_recursive(top_dir);
+ return -ENOMEM;
+}
+
+static void hwlat_tracer_start(struct trace_array *tr)
+{
+ int err;
+
+ err = start_kthread(tr);
+ if (err)
+ pr_err(BANNER "Cannot start hwlat kthread\n");
+}
+
+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 */
+ if (hwlat_busy)
+ return -EBUSY;
+
+ hwlat_trace = tr;
+
+ hwlat_data.count = 0;
+ tr->max_latency = 0;
+ save_tracing_thresh = tracing_thresh;
+
+ /* tracing_thresh is in nsecs, we speak in usecs */
+ if (!tracing_thresh)
+ tracing_thresh = last_tracing_thresh;
+
+ if (tracer_tracing_is_on(tr))
+ hwlat_tracer_start(tr);
+
+ hwlat_busy = true;
+
+ return 0;
+}
+
+static void hwlat_tracer_reset(struct trace_array *tr)
+{
+ stop_kthread();
+
+ /* the tracing threshold is static between runs */
+ last_tracing_thresh = tracing_thresh;
+
+ tracing_thresh = save_tracing_thresh;
+ hwlat_busy = false;
+}
+
+static struct tracer hwlat_tracer __read_mostly =
+{
+ .name = "hwlat",
+ .init = hwlat_tracer_init,
+ .reset = hwlat_tracer_reset,
+ .start = hwlat_tracer_start,
+ .stop = hwlat_tracer_stop,
+ .allow_instances = true,
+};
+
+__init static int init_hwlat_tracer(void)
+{
+ int ret;
+
+ mutex_init(&hwlat_data.lock);
+
+ ret = register_tracer(&hwlat_tracer);
+ if (ret)
+ return ret;
+
+ init_tracefs();
+
+ return 0;
+}
+late_initcall(init_hwlat_tracer);
projects / GitHub / moto-9609 / android_kernel_motorola_exynos9610.git / commitdiff