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