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author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-07 18:49:45 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-07 18:49:45 +0000 |
commit | 2c3c1048746a4622d8c89a29670120dc8fab93c4 (patch) | |
tree | 848558de17fb3008cdf4d861b01ac7781903ce39 /kernel/time/sched_clock.c | |
parent | Initial commit. (diff) | |
download | linux-upstream.tar.xz linux-upstream.zip |
Adding upstream version 6.1.76.upstream/6.1.76upstream
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to '')
-rw-r--r-- | kernel/time/sched_clock.c | 296 |
1 files changed, 296 insertions, 0 deletions
diff --git a/kernel/time/sched_clock.c b/kernel/time/sched_clock.c new file mode 100644 index 000000000..8464c5acc --- /dev/null +++ b/kernel/time/sched_clock.c @@ -0,0 +1,296 @@ +// 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/math.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> + +#include "timekeeping.h" + +/** + * 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_latch_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; +} + +notrace struct clock_read_data *sched_clock_read_begin(unsigned int *seq) +{ + *seq = raw_read_seqcount_latch(&cd.seq); + return cd.read_data + (*seq & 1); +} + +notrace int sched_clock_read_retry(unsigned int seq) +{ + return read_seqcount_latch_retry(&cd.seq, seq); +} + +unsigned long long notrace sched_clock(void) +{ + u64 cyc, res; + unsigned int seq; + struct clock_read_data *rd; + + do { + rd = sched_clock_read_begin(&seq); + + 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 (sched_clock_read_retry(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, flags; + char r_unit; + struct clock_read_data rd; + + if (cd.rate > rate) + return; + + /* Cannot register a sched_clock with interrupts on */ + local_irq_save(flags); + + /* 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_HARD); + } + + r = rate; + if (r >= 4000000) { + r = DIV_ROUND_CLOSEST(r, 1000000); + r_unit = 'M'; + } else if (r >= 4000) { + r = DIV_ROUND_CLOSEST(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(); + + local_irq_restore(flags); + + pr_debug("Registered %pS 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. + */ + 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_HARD); + sched_clock_timer.function = sched_clock_poll; + hrtimer_start(&sched_clock_timer, cd.wrap_kt, HRTIMER_MODE_REL_HARD); +} + +/* + * 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_latch(&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_HARD); + 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); |