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authorPeter Zijlstra <peterz@infradead.org>2020-07-16 08:11:24 +0300
committerWill Deacon <will@kernel.org>2020-07-20 13:50:47 +0300
commit1b86abc1c645ad5c9c7bf70910cb3ce73939d2d7 (patch)
tree8f72d9b938e23f26de7f0be72a0e11efc77c8b1c /include/linux/sched_clock.h
parent539707caa1a89ee4efc57b4e4231c20c46575ccc (diff)
downloadlinux-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.h28
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,