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| author | Peter Zijlstra <peterz@infradead.org> | 2020-07-16 08:11:24 +0300 |
|---|---|---|
| committer | Will Deacon <will@kernel.org> | 2020-07-20 13:50:47 +0300 |
| commit | 1b86abc1c645ad5c9c7bf70910cb3ce73939d2d7 (patch) | |
| tree | 8f72d9b938e23f26de7f0be72a0e11efc77c8b1c /include/linux/sched_clock.h | |
| parent | 539707caa1a89ee4efc57b4e4231c20c46575ccc (diff) | |
| download | linux-1b86abc1c645ad5c9c7bf70910cb3ce73939d2d7.tar.xz | |
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 'include/linux/sched_clock.h')
| -rw-r--r-- | include/linux/sched_clock.h | 28 |
1 files changed, 28 insertions, 0 deletions
diff --git a/include/linux/sched_clock.h b/include/linux/sched_clock.h index 0bb04a96a6d4..528718e4ed52 100644 --- a/include/linux/sched_clock.h +++ b/include/linux/sched_clock.h @@ -6,6 +6,34 @@ #define LINUX_SCHED_CLOCK #ifdef CONFIG_GENERIC_SCHED_CLOCK +/** + * 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; +}; + +extern struct clock_read_data *sched_clock_read_begin(unsigned int *seq); +extern int sched_clock_read_retry(unsigned int seq); + extern void generic_sched_clock_init(void); extern void sched_clock_register(u64 (*read)(void), int bits, |