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author | 2020-07-16 13:11:24 +0800 | |
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committer | 2020-07-20 11:50:47 +0100 | |
commit | 1b86abc1c645ad5c9c7bf70910cb3ce73939d2d7 (patch) | |
tree | 8f72d9b938e23f26de7f0be72a0e11efc77c8b1c /kernel/time | |
parent | arm64: perf: Correct the event index in sysfs (diff) | |
download | linux-1b86abc1c645ad5c9c7bf70910cb3ce73939d2d7.tar.gz linux-1b86abc1c645ad5c9c7bf70910cb3ce73939d2d7.tar.bz2 linux-1b86abc1c645ad5c9c7bf70910cb3ce73939d2d7.zip |
sched_clock: Expose struct clock_read_data
In order to support perf_event_mmap_page::cap_time features, an
architecture needs, aside from a userspace readable counter register,
to expose the exact clock data so that userspace can convert the
counter register into a correct timestamp.
Provide struct clock_read_data and two (seqcount) helpers so that
architectures (arm64 in specific) can expose the numbers to userspace.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Leo Yan <leo.yan@linaro.org>
Link: https://lore.kernel.org/r/20200716051130.4359-2-leo.yan@linaro.org
Signed-off-by: Will Deacon <will@kernel.org>
Diffstat (limited to 'kernel/time')
-rw-r--r-- | kernel/time/sched_clock.c | 41 |
1 files changed, 13 insertions, 28 deletions
diff --git a/kernel/time/sched_clock.c b/kernel/time/sched_clock.c index fa3f800d7d76..0acaadc3156c 100644 --- a/kernel/time/sched_clock.c +++ b/kernel/time/sched_clock.c @@ -20,31 +20,6 @@ #include "timekeeping.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) * @@ -93,6 +68,17 @@ static inline u64 notrace cyc_to_ns(u64 cyc, u32 mult, u32 shift) return (cyc * mult) >> shift; } +struct clock_read_data *sched_clock_read_begin(unsigned int *seq) +{ + *seq = raw_read_seqcount(&cd.seq); + return cd.read_data + (*seq & 1); +} + +int sched_clock_read_retry(unsigned int seq) +{ + return read_seqcount_retry(&cd.seq, seq); +} + unsigned long long notrace sched_clock(void) { u64 cyc, res; @@ -100,13 +86,12 @@ unsigned long long notrace sched_clock(void) struct clock_read_data *rd; do { - seq = raw_read_seqcount(&cd.seq); - rd = cd.read_data + (seq & 1); + 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 (read_seqcount_retry(&cd.seq, seq)); + } while (sched_clock_read_retry(seq)); return res; } |