#include <linux/seqlock.h>
#include <linux/bitops.h>
-struct clock_data {
- ktime_t wrap_kt;
+/**
+ * struct clock_read_data - data required to read from sched_clock
+ *
+ * @epoch_ns: sched_clock value at last update
+ * @epoch_cyc: Clock cycle value at last update
+ * @sched_clock_mask: Bitmask for two's complement subtraction of non 64bit
+ * clocks
+ * @read_sched_clock: Current clock source (or dummy source when suspended)
+ * @mult: Multipler for scaled math conversion
+ * @shift: Shift value for scaled math conversion
+ *
+ * Care must be taken when updating this structure; it is read by
+ * some very hot code paths. It occupies <=40 bytes and, when combined
+ * with the seqcount used to synchronize access, comfortably fits into
+ * a 64 byte cache line.
+ */
+struct clock_read_data {
u64 epoch_ns;
u64 epoch_cyc;
- seqcount_t seq;
- unsigned long rate;
+ u64 sched_clock_mask;
+ u64 (*read_sched_clock)(void);
u32 mult;
u32 shift;
- bool suspended;
+};
+
+/**
+ * struct clock_data - all data needed for sched_clock (including
+ * registration of a new clock source)
+ *
+ * @seq: Sequence counter for protecting updates.
+ * @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 clock read function
+ *
+ * The ordering of this structure has been chosen to optimize cache
+ * performance. In particular seq and read_data (combined) should fit
+ * into a single 64 byte cache line.
+ */
+struct clock_data {
+ seqcount_t seq;
+ struct clock_read_data read_data;
+ ktime_t wrap_kt;
+ unsigned long rate;
+ u64 (*actual_read_sched_clock)(void);
};
static struct hrtimer sched_clock_timer;
core_param(irqtime, irqtime, int, 0400);
-static struct clock_data cd = {
- .mult = NSEC_PER_SEC / HZ,
-};
-
-static u64 __read_mostly sched_clock_mask;
-
static u64 notrace jiffy_sched_clock_read(void)
{
/*
return (u64)(jiffies - INITIAL_JIFFIES);
}
-static u64 __read_mostly (*read_sched_clock)(void) = jiffy_sched_clock_read;
+static struct clock_data cd ____cacheline_aligned = {
+ .read_data = { .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)
{
unsigned long long notrace sched_clock(void)
{
- u64 epoch_ns;
- u64 epoch_cyc;
- u64 cyc;
+ u64 cyc, res;
unsigned long seq;
-
- if (cd.suspended)
- return cd.epoch_ns;
+ struct clock_read_data *rd = &cd.read_data;
do {
seq = raw_read_seqcount_begin(&cd.seq);
- epoch_cyc = cd.epoch_cyc;
- epoch_ns = cd.epoch_ns;
+
+ 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 (read_seqcount_retry(&cd.seq, seq));
- cyc = read_sched_clock();
- cyc = (cyc - epoch_cyc) & sched_clock_mask;
- return epoch_ns + cyc_to_ns(cyc, cd.mult, cd.shift);
+ return res;
}
/*
* Atomically update the sched_clock epoch.
*/
-static void notrace update_sched_clock(void)
+static void update_sched_clock(void)
{
unsigned long flags;
u64 cyc;
u64 ns;
+ struct clock_read_data *rd = &cd.read_data;
- cyc = read_sched_clock();
- ns = cd.epoch_ns +
- cyc_to_ns((cyc - cd.epoch_cyc) & sched_clock_mask,
- cd.mult, cd.shift);
+ 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);
raw_local_irq_save(flags);
raw_write_seqcount_begin(&cd.seq);
- cd.epoch_ns = ns;
- cd.epoch_cyc = cyc;
+ rd->epoch_ns = ns;
+ rd->epoch_cyc = cyc;
raw_write_seqcount_end(&cd.seq);
raw_local_irq_restore(flags);
}
{
u64 res, wrap, new_mask, new_epoch, cyc, ns;
u32 new_mult, new_shift;
- ktime_t new_wrap_kt;
unsigned long r;
char r_unit;
+ struct clock_read_data *rd = &cd.read_data;
if (cd.rate > rate)
return;
clocks_calc_mult_shift(&new_mult, &new_shift, rate, NSEC_PER_SEC, 3600);
new_mask = CLOCKSOURCE_MASK(bits);
+ cd.rate = rate;
- /* calculate how many ns until we wrap */
- wrap = clocks_calc_max_nsecs(new_mult, new_shift, 0, new_mask);
- new_wrap_kt = ns_to_ktime(wrap - (wrap >> 3));
+ /* 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);
/* update epoch for new counter and update epoch_ns from old counter*/
new_epoch = read();
- cyc = read_sched_clock();
- ns = cd.epoch_ns + cyc_to_ns((cyc - cd.epoch_cyc) & sched_clock_mask,
- cd.mult, cd.shift);
+ 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;
raw_write_seqcount_begin(&cd.seq);
- read_sched_clock = read;
- sched_clock_mask = new_mask;
- cd.rate = rate;
- cd.wrap_kt = new_wrap_kt;
- cd.mult = new_mult;
- cd.shift = new_shift;
- cd.epoch_cyc = new_epoch;
- cd.epoch_ns = ns;
+ 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;
raw_write_seqcount_end(&cd.seq);
r = rate;
* If no sched_clock function has been provided at that point,
* make it the final one one.
*/
- if (read_sched_clock == jiffy_sched_clock_read)
+ if (cd.actual_read_sched_clock == jiffy_sched_clock_read)
sched_clock_register(jiffy_sched_clock_read, BITS_PER_LONG, HZ);
update_sched_clock();
hrtimer_start(&sched_clock_timer, cd.wrap_kt, HRTIMER_MODE_REL);
}
+/*
+ * 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.
+ */
+static u64 notrace suspended_sched_clock_read(void)
+{
+ return cd.read_data.epoch_cyc;
+}
+
static int sched_clock_suspend(void)
{
+ struct clock_read_data *rd = &cd.read_data;
+
update_sched_clock();
hrtimer_cancel(&sched_clock_timer);
- cd.suspended = true;
+ rd->read_sched_clock = suspended_sched_clock_read;
return 0;
}
static void sched_clock_resume(void)
{
- cd.epoch_cyc = read_sched_clock();
+ struct clock_read_data *rd = &cd.read_data;
+
+ rd->epoch_cyc = cd.actual_read_sched_clock();
hrtimer_start(&sched_clock_timer, cd.wrap_kt, HRTIMER_MODE_REL);
- cd.suspended = false;
+ rd->read_sched_clock = cd.actual_read_sched_clock;
}
static struct syscore_ops sched_clock_ops = {