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-rw-r--r--kernel/time/sched_clock.c297
1 files changed, 297 insertions, 0 deletions
diff --git a/kernel/time/sched_clock.c b/kernel/time/sched_clock.c
new file mode 100644
index 000000000..b1b9b1289
--- /dev/null
+++ b/kernel/time/sched_clock.c
@@ -0,0 +1,297 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Generic sched_clock() support, to extend low level hardware time
+ * counters to full 64-bit ns values.
+ */
+#include <linux/clocksource.h>
+#include <linux/init.h>
+#include <linux/jiffies.h>
+#include <linux/ktime.h>
+#include <linux/kernel.h>
+#include <linux/moduleparam.h>
+#include <linux/sched.h>
+#include <linux/sched/clock.h>
+#include <linux/syscore_ops.h>
+#include <linux/hrtimer.h>
+#include <linux/sched_clock.h>
+#include <linux/seqlock.h>
+#include <linux/bitops.h>
+
+#include "timekeeping.h"
+
+/**
+ * struct clock_data - all data needed for sched_clock() (including
+ * registration of a new clock source)
+ *
+ * @seq: Sequence counter for protecting updates. The lowest
+ * bit is the index for @read_data.
+ * @read_data: Data required to read from sched_clock.
+ * @wrap_kt: Duration for which clock can run before wrapping.
+ * @rate: Tick rate of the registered clock.
+ * @actual_read_sched_clock: Registered hardware level clock read function.
+ *
+ * The ordering of this structure has been chosen to optimize cache
+ * performance. In particular 'seq' and 'read_data[0]' (combined) should fit
+ * into a single 64-byte cache line.
+ */
+struct clock_data {
+ seqcount_latch_t seq;
+ struct clock_read_data read_data[2];
+ ktime_t wrap_kt;
+ unsigned long rate;
+
+ u64 (*actual_read_sched_clock)(void);
+};
+
+static struct hrtimer sched_clock_timer;
+static int irqtime = -1;
+
+core_param(irqtime, irqtime, int, 0400);
+
+static u64 notrace jiffy_sched_clock_read(void)
+{
+ /*
+ * We don't need to use get_jiffies_64 on 32-bit arches here
+ * because we register with BITS_PER_LONG
+ */
+ return (u64)(jiffies - INITIAL_JIFFIES);
+}
+
+static struct clock_data cd ____cacheline_aligned = {
+ .read_data[0] = { .mult = NSEC_PER_SEC / HZ,
+ .read_sched_clock = jiffy_sched_clock_read, },
+ .actual_read_sched_clock = jiffy_sched_clock_read,
+};
+
+static inline u64 notrace cyc_to_ns(u64 cyc, u32 mult, u32 shift)
+{
+ return (cyc * mult) >> shift;
+}
+
+notrace struct clock_read_data *sched_clock_read_begin(unsigned int *seq)
+{
+ *seq = raw_read_seqcount_latch(&cd.seq);
+ return cd.read_data + (*seq & 1);
+}
+
+notrace int sched_clock_read_retry(unsigned int seq)
+{
+ return read_seqcount_latch_retry(&cd.seq, seq);
+}
+
+unsigned long long notrace sched_clock(void)
+{
+ u64 cyc, res;
+ unsigned int seq;
+ struct clock_read_data *rd;
+
+ do {
+ rd = sched_clock_read_begin(&seq);
+
+ cyc = (rd->read_sched_clock() - rd->epoch_cyc) &
+ rd->sched_clock_mask;
+ res = rd->epoch_ns + cyc_to_ns(cyc, rd->mult, rd->shift);
+ } while (sched_clock_read_retry(seq));
+
+ return res;
+}
+
+/*
+ * Updating the data required to read the clock.
+ *
+ * sched_clock() will never observe mis-matched data even if called from
+ * an NMI. We do this by maintaining an odd/even copy of the data and
+ * steering sched_clock() to one or the other using a sequence counter.
+ * In order to preserve the data cache profile of sched_clock() as much
+ * as possible the system reverts back to the even copy when the update
+ * completes; the odd copy is used *only* during an update.
+ */
+static void update_clock_read_data(struct clock_read_data *rd)
+{
+ /* update the backup (odd) copy with the new data */
+ cd.read_data[1] = *rd;
+
+ /* steer readers towards the odd copy */
+ raw_write_seqcount_latch(&cd.seq);
+
+ /* now its safe for us to update the normal (even) copy */
+ cd.read_data[0] = *rd;
+
+ /* switch readers back to the even copy */
+ raw_write_seqcount_latch(&cd.seq);
+}
+
+/*
+ * Atomically update the sched_clock() epoch.
+ */
+static void update_sched_clock(void)
+{
+ u64 cyc;
+ u64 ns;
+ struct clock_read_data rd;
+
+ rd = cd.read_data[0];
+
+ cyc = cd.actual_read_sched_clock();
+ ns = rd.epoch_ns + cyc_to_ns((cyc - rd.epoch_cyc) & rd.sched_clock_mask, rd.mult, rd.shift);
+
+ rd.epoch_ns = ns;
+ rd.epoch_cyc = cyc;
+
+ update_clock_read_data(&rd);
+}
+
+static enum hrtimer_restart sched_clock_poll(struct hrtimer *hrt)
+{
+ update_sched_clock();
+ hrtimer_forward_now(hrt, cd.wrap_kt);
+
+ return HRTIMER_RESTART;
+}
+
+void __init
+sched_clock_register(u64 (*read)(void), int bits, unsigned long rate)
+{
+ u64 res, wrap, new_mask, new_epoch, cyc, ns;
+ u32 new_mult, new_shift;
+ unsigned long r, flags;
+ char r_unit;
+ struct clock_read_data rd;
+
+ if (cd.rate > rate)
+ return;
+
+ /* Cannot register a sched_clock with interrupts on */
+ local_irq_save(flags);
+
+ /* Calculate the mult/shift to convert counter ticks to ns. */
+ clocks_calc_mult_shift(&new_mult, &new_shift, rate, NSEC_PER_SEC, 3600);
+
+ new_mask = CLOCKSOURCE_MASK(bits);
+ cd.rate = rate;
+
+ /* Calculate how many nanosecs until we risk wrapping */
+ wrap = clocks_calc_max_nsecs(new_mult, new_shift, 0, new_mask, NULL);
+ cd.wrap_kt = ns_to_ktime(wrap);
+
+ rd = cd.read_data[0];
+
+ /* Update epoch for new counter and update 'epoch_ns' from old counter*/
+ new_epoch = read();
+ cyc = cd.actual_read_sched_clock();
+ ns = rd.epoch_ns + cyc_to_ns((cyc - rd.epoch_cyc) & rd.sched_clock_mask, rd.mult, rd.shift);
+ cd.actual_read_sched_clock = read;
+
+ rd.read_sched_clock = read;
+ rd.sched_clock_mask = new_mask;
+ rd.mult = new_mult;
+ rd.shift = new_shift;
+ rd.epoch_cyc = new_epoch;
+ rd.epoch_ns = ns;
+
+ update_clock_read_data(&rd);
+
+ if (sched_clock_timer.function != NULL) {
+ /* update timeout for clock wrap */
+ hrtimer_start(&sched_clock_timer, cd.wrap_kt,
+ HRTIMER_MODE_REL_HARD);
+ }
+
+ r = rate;
+ if (r >= 4000000) {
+ r /= 1000000;
+ r_unit = 'M';
+ } else {
+ if (r >= 1000) {
+ r /= 1000;
+ r_unit = 'k';
+ } else {
+ r_unit = ' ';
+ }
+ }
+
+ /* Calculate the ns resolution of this counter */
+ res = cyc_to_ns(1ULL, new_mult, new_shift);
+
+ pr_info("sched_clock: %u bits at %lu%cHz, resolution %lluns, wraps every %lluns\n",
+ bits, r, r_unit, res, wrap);
+
+ /* Enable IRQ time accounting if we have a fast enough sched_clock() */
+ if (irqtime > 0 || (irqtime == -1 && rate >= 1000000))
+ enable_sched_clock_irqtime();
+
+ local_irq_restore(flags);
+
+ pr_debug("Registered %pS as sched_clock source\n", read);
+}
+
+void __init generic_sched_clock_init(void)
+{
+ /*
+ * If no sched_clock() function has been provided at that point,
+ * make it the final one.
+ */
+ if (cd.actual_read_sched_clock == jiffy_sched_clock_read)
+ sched_clock_register(jiffy_sched_clock_read, BITS_PER_LONG, HZ);
+
+ update_sched_clock();
+
+ /*
+ * Start the timer to keep sched_clock() properly updated and
+ * sets the initial epoch.
+ */
+ hrtimer_init(&sched_clock_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL_HARD);
+ sched_clock_timer.function = sched_clock_poll;
+ hrtimer_start(&sched_clock_timer, cd.wrap_kt, HRTIMER_MODE_REL_HARD);
+}
+
+/*
+ * Clock read function for use when the clock is suspended.
+ *
+ * This function makes it appear to sched_clock() as if the clock
+ * stopped counting at its last update.
+ *
+ * This function must only be called from the critical
+ * section in sched_clock(). It relies on the read_seqcount_retry()
+ * at the end of the critical section to be sure we observe the
+ * correct copy of 'epoch_cyc'.
+ */
+static u64 notrace suspended_sched_clock_read(void)
+{
+ unsigned int seq = raw_read_seqcount_latch(&cd.seq);
+
+ return cd.read_data[seq & 1].epoch_cyc;
+}
+
+int sched_clock_suspend(void)
+{
+ struct clock_read_data *rd = &cd.read_data[0];
+
+ update_sched_clock();
+ hrtimer_cancel(&sched_clock_timer);
+ rd->read_sched_clock = suspended_sched_clock_read;
+
+ return 0;
+}
+
+void sched_clock_resume(void)
+{
+ struct clock_read_data *rd = &cd.read_data[0];
+
+ rd->epoch_cyc = cd.actual_read_sched_clock();
+ hrtimer_start(&sched_clock_timer, cd.wrap_kt, HRTIMER_MODE_REL_HARD);
+ rd->read_sched_clock = cd.actual_read_sched_clock;
+}
+
+static struct syscore_ops sched_clock_ops = {
+ .suspend = sched_clock_suspend,
+ .resume = sched_clock_resume,
+};
+
+static int __init sched_clock_syscore_init(void)
+{
+ register_syscore_ops(&sched_clock_ops);
+
+ return 0;
+}
+device_initcall(sched_clock_syscore_init);