| // 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> |
| |
| /** |
| * 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; |
| u64 sched_clock_mask; |
| u64 (*read_sched_clock)(void); |
| u32 mult; |
| u32 shift; |
| }; |
| |
| /** |
| * 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_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; |
| } |
| |
| unsigned long long notrace sched_clock(void) |
| { |
| u64 cyc, res; |
| unsigned int seq; |
| struct clock_read_data *rd; |
| |
| do { |
| seq = raw_read_seqcount(&cd.seq); |
| rd = cd.read_data + (seq & 1); |
| |
| 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)); |
| |
| 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; |
| char r_unit; |
| struct clock_read_data rd; |
| |
| if (cd.rate > rate) |
| return; |
| |
| WARN_ON(!irqs_disabled()); |
| |
| /* 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); |
| } |
| |
| 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(); |
| |
| pr_debug("Registered %pF 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 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); |
| sched_clock_timer.function = sched_clock_poll; |
| 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. |
| * |
| * 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(&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); |
| 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); |