/*
- * sched_clock.c: support for extending counters to full 64-bit ns counter
+ * sched_clock.c: Generic sched_clock() support, to extend low level
+ * hardware time counters to full 64-bit ns values.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
#include <linux/bitops.h>
/**
- * struct clock_read_data - data required to read from sched_clock
+ * 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
+ * @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
+ * 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
};
/**
- * struct clock_data - all data needed for sched_clock (including
+ * 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 clock read function
+ * @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.
+ * performance. In particular 'seq' and 'read_data[0]' (combined) should fit
+ * into a single 64-byte cache line.
*/
struct clock_data {
- seqcount_t seq;
- struct clock_read_data read_data[2];
- ktime_t wrap_kt;
- unsigned long rate;
+ seqcount_t seq;
+ struct clock_read_data read_data[2];
+ ktime_t wrap_kt;
+ unsigned long rate;
+
u64 (*actual_read_sched_clock)(void);
};
/*
* Updating the data required to read the clock.
*
- * sched_clock will never observe mis-matched data even if called from
+ * 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
+ * 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.
*/
}
/*
- * Atomically update the sched_clock epoch.
+ * Atomically update the sched_clock() epoch.
*/
static void update_sched_clock(void)
{
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);
+ 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_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)
+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;
WARN_ON(!irqs_disabled());
- /* calculate the mult/shift to convert counter ticks to ns. */
+ /* 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 */
+ /* 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*/
+ /* 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);
+ 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;
+ 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);
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 */
+ } 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 */
+ /* Enable IRQ time accounting if we have a fast enough sched_clock() */
if (irqtime > 0 || (irqtime == -1 && rate >= 1000000))
enable_sched_clock_irqtime();
void __init sched_clock_postinit(void)
{
/*
- * If no sched_clock function has been provided at that point,
+ * If no sched_clock() function has been provided at that point,
* make it the final one one.
*/
if (cd.actual_read_sched_clock == jiffy_sched_clock_read)
* 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.
+ * correct copy of 'epoch_cyc'.
*/
static u64 notrace suspended_sched_clock_read(void)
{
update_sched_clock();
hrtimer_cancel(&sched_clock_timer);
rd->read_sched_clock = suspended_sched_clock_read;
+
return 0;
}
}
static struct syscore_ops sched_clock_ops = {
- .suspend = sched_clock_suspend,
- .resume = sched_clock_resume,
+ .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);
projects / linux-2.6-block.git / commitdiff