jrcu: make sampling interval user adjustable.
By default jrcu runs at 20 Hz. The user can now change
that as shown in the below example. Accepts any integer
between 1 and 1000, inclusive.
echo hz=100 >/sys/kernel/debug/rcu/rcudata
This should make it easier to stress-test JRCU.
Signed-off-by: Joe Korty <[email protected]>
Index: b/kernel/jrcu.c
===================================================================
--- a/kernel/jrcu.c
+++ b/kernel/jrcu.c
@@ -38,12 +38,14 @@
#include <linux/bug.h>
#include <linux/smp.h>
+#include <linux/ctype.h>
#include <linux/sched.h>
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/percpu.h>
#include <linux/stddef.h>
+#include <linux/string.h>
#include <linux/preempt.h>
#include <linux/compiler.h>
#include <linux/irqflags.h>
@@ -102,8 +104,6 @@ static inline void rcu_list_join(struct
}
-#define RCU_HZ 20 /* max rate at which batches are retired */
-
struct rcu_data {
u8 wait; /* goes false when this cpu consents to
* the retirement of the current batch */
@@ -123,6 +123,14 @@ static struct rcu_stats {
unsigned nforced; /* #forced eobs (should be zero) */
} rcu_stats;
+#define RCU_HZ (20)
+#define RCU_HZ_PERIOD_US (USEC_PER_SEC / RCU_HZ)
+#define RCU_HZ_DELTA_US (USEC_PER_SEC / (HZ * 3 / 2))
+
+int rcu_hz = RCU_HZ;
+int rcu_hz_period_us = RCU_HZ_PERIOD_US;
+int rcu_hz_delta_us = RCU_HZ_DELTA_US;
+
int rcu_scheduler_active __read_mostly;
int rcu_nmi_seen __read_mostly;
static u64 rcu_timestamp;
@@ -387,11 +395,8 @@ static void rcu_delimit_batches(void)
#include <linux/hrtimer.h>
#include <linux/interrupt.h>
-#define RCU_PERIOD_NS (NSEC_PER_SEC / RCU_HZ)
-#define RCU_PERIOD_DELTA_NS (((NSEC_PER_SEC / HZ) * 3) / 2)
-
-#define RCU_PERIOD_MIN_NS RCU_PERIOD_NS
-#define RCU_PERIOD_MAX_NS (RCU_PERIOD_NS + RCU_PERIOD_DELTA_NS)
+#define rcu_hz_period_ns (rcu_hz_period_us * NSEC_PER_USEC)
+#define rcu_hz_delta_ns (rcu_hz_delta_us * NSEC_PER_USEC)
static struct hrtimer rcu_timer;
@@ -406,15 +411,15 @@ static enum hrtimer_restart rcu_timer_fu
raise_softirq(RCU_SOFTIRQ);
- next = ktime_add_ns(ktime_get(), RCU_PERIOD_NS);
- hrtimer_set_expires_range_ns(&rcu_timer, next, RCU_PERIOD_DELTA_NS);
+ next = ktime_add_ns(ktime_get(), rcu_hz_period_ns);
+ hrtimer_set_expires_range_ns(&rcu_timer, next, rcu_hz_delta_ns);
return HRTIMER_RESTART;
}
static void rcu_timer_restart(void)
{
pr_info("JRCU: starting timer. rate is %d Hz\n", RCU_HZ);
- hrtimer_forward_now(&rcu_timer, ns_to_ktime(RCU_PERIOD_NS));
+ hrtimer_forward_now(&rcu_timer, ns_to_ktime(rcu_hz_period_ns));
hrtimer_start_expires(&rcu_timer, HRTIMER_MODE_ABS);
}
@@ -471,9 +476,6 @@ void __init rcu_scheduler_starting(void)
/* ------------------ daemon driver section --------------------- */
-#define RCU_PERIOD_MIN_US (RCU_PERIOD_MIN_NS / NSEC_PER_USEC)
-#define RCU_PERIOD_MAX_US (RCU_PERIOD_MAX_NS / NSEC_PER_USEC)
-
/*
* Once the system is fully up, we will drive the periodic-polling part
* of JRCU from a kernel daemon, jrcud. Until then it is driven by
@@ -492,7 +494,7 @@ static int jrcud_func(void *arg)
rcu_timer_stop();
while (!kthread_should_stop()) {
- usleep_range(RCU_PERIOD_MIN_US, RCU_PERIOD_MAX_US);
+ usleep_range(rcu_hz_period_us, rcu_hz_period_us + rcu_hz_delta_us);
rcu_delimit_batches();
}
@@ -531,6 +533,8 @@ static int rcu_debugfs_show(struct seq_f
msecs = div_s64(sched_clock() - rcu_timestamp, NSEC_PER_MSEC);
raw_local_irq_enable();
+ seq_printf(m, "%14u: hz\n",
+ rcu_hz);
seq_printf(m, "%14u: #passes seen\n",
rcu_stats.npasses);
seq_printf(m, "%14u: #batches seen\n",
@@ -580,6 +584,57 @@ static int rcu_debugfs_show(struct seq_f
return 0;
}
+static ssize_t rcu_debugfs_write(struct file *file,
+ const char __user *buffer, size_t count, loff_t *ppos)
+{
+ int i, j, c;
+ char token[32];
+
+ if (!capable(CAP_SYS_ADMIN))
+ return -EPERM;
+
+ if (count <= 0)
+ return count;
+
+ if (!access_ok(VERIFY_READ, buffer, count))
+ return -EFAULT;
+
+ i = 0;
+ if (__get_user(c, &buffer[i++]))
+ return -EFAULT;
+
+ /* Token extractor -- first, skip leading whitepace */
+ while (c && isspace(c) && i < count) {
+ if (__get_user(c, &buffer[i++]))
+ return -EFAULT;
+ }
+
+ if (i >= count || c == 0)
+ return count; /* all done, no more tokens */
+
+ j = 0;
+ do {
+ if (j == (sizeof(token) - 1))
+ return -EINVAL;
+ token[j++] = c;
+ if (__get_user(c, &buffer[i++]))
+ return -EFAULT;
+ } while (c && !isspace(c) && i < count); /* extract next token */
+ token[j++] = 0;
+
+ if (!strncmp(token, "hz=", 3)) {
+ int rcu_hz_wanted = -1;
+ sscanf(&token[3], "%d", &rcu_hz_wanted);
+ if (rcu_hz_wanted < 2 || rcu_hz_wanted > 1000)
+ return -EINVAL;
+ rcu_hz = rcu_hz_wanted;
+ rcu_hz_period_us = USEC_PER_SEC / rcu_hz;
+ } else
+ return -EINVAL;
+
+ return count;
+}
+
static int rcu_debugfs_open(struct inode *inode, struct file *file)
{
return single_open(file, rcu_debugfs_show, NULL);
@@ -589,6 +644,7 @@ static const struct file_operations rcu_
.owner = THIS_MODULE,
.open = rcu_debugfs_open,
.read = seq_read,
+ .write = rcu_debugfs_write,
.llseek = seq_lseek,
.release = single_release,
};
@@ -603,7 +659,7 @@ static int __init rcu_debugfs_init(void)
if (!rcudir)
goto error;
- retval = debugfs_create_file("rcudata", 0444, rcudir,
+ retval = debugfs_create_file("rcudata", 0644, rcudir,
NULL, &rcu_debugfs_fops);
if (!retval)
goto error;