From: Peter Zijlstra <pet...@infradead.org>
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) <pet...@infradead.org>
Signed-off-by: Leo Yan <leo....@linaro.org>
---
include/linux/sched_clock.h | 28 +++++++++++++++++++++++++
kernel/time/sched_clock.c | 41 ++++++++++++-------------------------
2 files changed, 41 insertions(+), 28 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,
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
@@ -19,31 +19,6 @@
#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;
}
--
2.17.1
