diff options
Diffstat (limited to 'kernel/time/timekeeping.c')
| -rw-r--r-- | kernel/time/timekeeping.c | 119 |
1 files changed, 95 insertions, 24 deletions
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c index 4c47f388a83f..6858a31364b6 100644 --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -54,6 +54,9 @@ static struct { static struct timekeeper shadow_timekeeper; +/* flag for if timekeeping is suspended */ +int __read_mostly timekeeping_suspended; + /** * struct tk_fast - NMI safe timekeeper * @seq: Sequence counter for protecting updates. The lowest bit @@ -64,7 +67,7 @@ static struct timekeeper shadow_timekeeper; * See @update_fast_timekeeper() below. */ struct tk_fast { - seqcount_raw_spinlock_t seq; + seqcount_latch_t seq; struct tk_read_base base[2]; }; @@ -73,28 +76,42 @@ static u64 cycles_at_suspend; static u64 dummy_clock_read(struct clocksource *cs) { - return cycles_at_suspend; + if (timekeeping_suspended) + return cycles_at_suspend; + return local_clock(); } static struct clocksource dummy_clock = { .read = dummy_clock_read, }; +/* + * Boot time initialization which allows local_clock() to be utilized + * during early boot when clocksources are not available. local_clock() + * returns nanoseconds already so no conversion is required, hence mult=1 + * and shift=0. When the first proper clocksource is installed then + * the fast time keepers are updated with the correct values. + */ +#define FAST_TK_INIT \ + { \ + .clock = &dummy_clock, \ + .mask = CLOCKSOURCE_MASK(64), \ + .mult = 1, \ + .shift = 0, \ + } + static struct tk_fast tk_fast_mono ____cacheline_aligned = { - .seq = SEQCNT_RAW_SPINLOCK_ZERO(tk_fast_mono.seq, &timekeeper_lock), - .base[0] = { .clock = &dummy_clock, }, - .base[1] = { .clock = &dummy_clock, }, + .seq = SEQCNT_LATCH_ZERO(tk_fast_mono.seq), + .base[0] = FAST_TK_INIT, + .base[1] = FAST_TK_INIT, }; static struct tk_fast tk_fast_raw ____cacheline_aligned = { - .seq = SEQCNT_RAW_SPINLOCK_ZERO(tk_fast_raw.seq, &timekeeper_lock), - .base[0] = { .clock = &dummy_clock, }, - .base[1] = { .clock = &dummy_clock, }, + .seq = SEQCNT_LATCH_ZERO(tk_fast_raw.seq), + .base[0] = FAST_TK_INIT, + .base[1] = FAST_TK_INIT, }; -/* flag for if timekeeping is suspended */ -int __read_mostly timekeeping_suspended; - static inline void tk_normalize_xtime(struct timekeeper *tk) { while (tk->tkr_mono.xtime_nsec >= ((u64)NSEC_PER_SEC << tk->tkr_mono.shift)) { @@ -467,7 +484,7 @@ static __always_inline u64 __ktime_get_fast_ns(struct tk_fast *tkf) tk_clock_read(tkr), tkr->cycle_last, tkr->mask)); - } while (read_seqcount_retry(&tkf->seq, seq)); + } while (read_seqcount_latch_retry(&tkf->seq, seq)); return now; } @@ -513,29 +530,29 @@ u64 notrace ktime_get_boot_fast_ns(void) } EXPORT_SYMBOL_GPL(ktime_get_boot_fast_ns); - /* * See comment for __ktime_get_fast_ns() vs. timestamp ordering */ -static __always_inline u64 __ktime_get_real_fast_ns(struct tk_fast *tkf) +static __always_inline u64 __ktime_get_real_fast(struct tk_fast *tkf, u64 *mono) { struct tk_read_base *tkr; + u64 basem, baser, delta; unsigned int seq; - u64 now; do { seq = raw_read_seqcount_latch(&tkf->seq); tkr = tkf->base + (seq & 0x01); - now = ktime_to_ns(tkr->base_real); + basem = ktime_to_ns(tkr->base); + baser = ktime_to_ns(tkr->base_real); - now += timekeeping_delta_to_ns(tkr, - clocksource_delta( - tk_clock_read(tkr), - tkr->cycle_last, - tkr->mask)); - } while (read_seqcount_retry(&tkf->seq, seq)); + delta = timekeeping_delta_to_ns(tkr, + clocksource_delta(tk_clock_read(tkr), + tkr->cycle_last, tkr->mask)); + } while (read_seqcount_latch_retry(&tkf->seq, seq)); - return now; + if (mono) + *mono = basem + delta; + return baser + delta; } /** @@ -543,11 +560,65 @@ static __always_inline u64 __ktime_get_real_fast_ns(struct tk_fast *tkf) */ u64 ktime_get_real_fast_ns(void) { - return __ktime_get_real_fast_ns(&tk_fast_mono); + return __ktime_get_real_fast(&tk_fast_mono, NULL); } EXPORT_SYMBOL_GPL(ktime_get_real_fast_ns); /** + * ktime_get_fast_timestamps: - NMI safe timestamps + * @snapshot: Pointer to timestamp storage + * + * Stores clock monotonic, boottime and realtime timestamps. + * + * Boot time is a racy access on 32bit systems if the sleep time injection + * happens late during resume and not in timekeeping_resume(). That could + * be avoided by expanding struct tk_read_base with boot offset for 32bit + * and adding more overhead to the update. As this is a hard to observe + * once per resume event which can be filtered with reasonable effort using + * the accurate mono/real timestamps, it's probably not worth the trouble. + * + * Aside of that it might be possible on 32 and 64 bit to observe the + * following when the sleep time injection happens late: + * + * CPU 0 CPU 1 + * timekeeping_resume() + * ktime_get_fast_timestamps() + * mono, real = __ktime_get_real_fast() + * inject_sleep_time() + * update boot offset + * boot = mono + bootoffset; + * + * That means that boot time already has the sleep time adjustment, but + * real time does not. On the next readout both are in sync again. + * + * Preventing this for 64bit is not really feasible without destroying the + * careful cache layout of the timekeeper because the sequence count and + * struct tk_read_base would then need two cache lines instead of one. + * + * Access to the time keeper clock source is disabled accross the innermost + * steps of suspend/resume. The accessors still work, but the timestamps + * are frozen until time keeping is resumed which happens very early. + * + * For regular suspend/resume there is no observable difference vs. sched + * clock, but it might affect some of the nasty low level debug printks. + * + * OTOH, access to sched clock is not guaranteed accross suspend/resume on + * all systems either so it depends on the hardware in use. + * + * If that turns out to be a real problem then this could be mitigated by + * using sched clock in a similar way as during early boot. But it's not as + * trivial as on early boot because it needs some careful protection + * against the clock monotonic timestamp jumping backwards on resume. + */ +void ktime_get_fast_timestamps(struct ktime_timestamps *snapshot) +{ + struct timekeeper *tk = &tk_core.timekeeper; + + snapshot->real = __ktime_get_real_fast(&tk_fast_mono, &snapshot->mono); + snapshot->boot = snapshot->mono + ktime_to_ns(data_race(tk->offs_boot)); +} + +/** * halt_fast_timekeeper - Prevent fast timekeeper from accessing clocksource. * @tk: Timekeeper to snapshot. * |