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Linux kernel mirror (for testing) git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
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#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 __always_inline u64 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 = 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);}
static __always_inline unsigned long long __sched_clock(void){ struct clock_read_data *rd; unsigned int seq; u64 cyc, res;
do { seq = raw_read_seqcount_latch(&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 (raw_read_seqcount_latch_retry(&cd.seq, seq));
return res;}
unsigned long long noinstr sched_clock_noinstr(void){ return __sched_clock();}
unsigned long long notrace sched_clock(void){ unsigned long long ns; preempt_disable_notrace(); /* * All of __sched_clock() is a seqcount_latch reader critical section, * but relies on the raw helpers which are uninstrumented. For KCSAN, * mark all accesses in __sched_clock() as atomic. */ kcsan_nestable_atomic_begin(); ns = __sched_clock(); kcsan_nestable_atomic_end(); preempt_enable_notrace(); return ns;}
/* * 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){ /* steer readers towards the odd copy */ write_seqcount_latch_begin(&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 */ write_seqcount_latch(&cd.seq);
/* update the backup (odd) copy with the new data */ cd.read_data[1] = *rd;
write_seqcount_latch_end(&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 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 (ACCESS_PRIVATE(&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);}EXPORT_SYMBOL_GPL(sched_clock_register);
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_setup(&sched_clock_timer, sched_clock_poll, CLOCK_MONOTONIC, HRTIMER_MODE_REL_HARD); 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 = 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;}
static int sched_clock_syscore_suspend(void *data){ return sched_clock_suspend();}
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 void sched_clock_syscore_resume(void *data){ sched_clock_resume();}
static const struct syscore_ops sched_clock_syscore_ops = { .suspend = sched_clock_syscore_suspend, .resume = sched_clock_syscore_resume,};
static struct syscore sched_clock_syscore = { .ops = &sched_clock_syscore_ops,};
static int __init sched_clock_syscore_init(void){ register_syscore(&sched_clock_syscore);
return 0;}device_initcall(sched_clock_syscore_init);