The branch main has been updated by rwatson:
URL:
https://cgit.FreeBSD.org/src/commit/?id=c3feaeaa32c9029ea98f2bb95c665390ca53728a
commit c3feaeaa32c9029ea98f2bb95c665390ca53728a
Author: Robert Watson <rwat...@freebsd.org>
AuthorDate: 2021-02-16 15:19:05 +0000
Commit: Robert Watson <rwat...@freebsd.org>
CommitDate: 2021-02-19 09:00:39 +0000
Reimplement the arm64 dtrace_gethrtime(), which provides the
high-resolution nanosecond timestamp used for the DTrace 'timestamp'
built-in variable. The new implementation uses the EL0 cycle
counter and frequency registers in ARMv8-A. This replaces a
previous implementation that relied on an instrumentation-safe
implementation of getnanotime(), which provided only timer
resolution.
MFC after: 3 days
Reviewed by: andrew, bsdimp (older version)
Useful comments appreciated: jrtc27, emaste
---
sys/cddl/dev/dtrace/aarch64/dtrace_subr.c | 23 +++++++++++++----------
1 file changed, 13 insertions(+), 10 deletions(-)
diff --git a/sys/cddl/dev/dtrace/aarch64/dtrace_subr.c
b/sys/cddl/dev/dtrace/aarch64/dtrace_subr.c
index 6646e51fc191..9bf9f0798bb5 100644
--- a/sys/cddl/dev/dtrace/aarch64/dtrace_subr.c
+++ b/sys/cddl/dev/dtrace/aarch64/dtrace_subr.c
@@ -153,23 +153,26 @@ dtrace_sync(void)
}
/*
- * DTrace needs a high resolution time function which can
- * be called from a probe context and guaranteed not to have
- * instrumented with probes itself.
+ * DTrace needs a high resolution time function which can be called from a
+ * probe context and guaranteed not to have instrumented with probes itself.
*
- * Returns nanoseconds since boot.
+ * Returns nanoseconds since some arbitrary point in time (likely SoC reset?).
*/
uint64_t
-dtrace_gethrtime()
+dtrace_gethrtime(void)
{
- struct timespec curtime;
-
- dtrace_getnanouptime(&curtime);
-
- return (curtime.tv_sec * 1000000000UL + curtime.tv_nsec);
+ uint64_t count, freq;
+ count = READ_SPECIALREG(cntvct_el0);
+ freq = READ_SPECIALREG(cntfrq_el0);
+ return ((1000000000UL * count) / freq);
}
+/*
+ * Return a much lower resolution wallclock time based on the system clock
+ * updated by the timer. If needed, we could add a version interpolated from
+ * the system clock as is the case with dtrace_gethrtime().
+ */
uint64_t
dtrace_gethrestime(void)
{
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