Date: Thu, 25 Feb 2021 21:42:11 GMT From: Robert Watson <rwatson@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-branches@FreeBSD.org Subject: git: bbcdd9faca55 - stable/13 - Reimplemen FreeBSD/arm64 dtrace_gethrtime() to use the system timer. dtrace_gethrtime() is the high-resolution nanosecond timestemp 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. Message-ID: <202102252142.11PLgBUi046599@gitrepo.freebsd.org>
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The branch stable/13 has been updated by rwatson: URL: https://cgit.FreeBSD.org/src/commit/?id=bbcdd9faca55758b228b949f1c1bb41b85e90a8e commit bbcdd9faca55758b228b949f1c1bb41b85e90a8e Author: Robert Watson <rwatson@FreeBSD.org> AuthorDate: 2021-02-16 15:19:05 +0000 Commit: Robert Watson <rwatson@FreeBSD.org> CommitDate: 2021-02-25 21:38:30 +0000 Reimplemen FreeBSD/arm64 dtrace_gethrtime() to use the system timer. dtrace_gethrtime() is the high-resolution nanosecond timestemp 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. Approved by: re (gjb) Reviewed by: andrew, bsdimp (older version) Useful comments appreciated: jrtc27, emaste Differential Revision: https://reviews.freebsd.org/D28723 --- 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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