/* * 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 * published by the Free Software Foundation. */ #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 long 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 long seq = raw_read_seqcount(&cd.seq); return cd.read_data[seq & 1].epoch_cyc; } static 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; } static 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);