Use struct vdso_timehands data to implement fast gettimeofday(2) and

clock_gettime(2) functions if supported. The speedup seen in
microbenchmarks is in range 4x-7x depending on the hardware.

Only amd64 and i386 architectures are supported. Libc uses rdtsc and
kernel data to calculate current time, if enabled by kernel.

Hopefully, this code is going to migrate into vdso in some future.

Discussed with:	bde
Reviewed by:	jhb
Tested by:	flo
MFC after:	1 month

1 files changed, 142 insertions, 0 deletions

diff --git a/lib/libc/sys/__vdso_gettimeofday.c b/lib/libc/sys/__vdso_gettimeofday.c
new file mode 100644
index 0000000..32abb69
--- /dev/null
+++ b/lib/libc/sys/__vdso_gettimeofday.c
@@ -0,0 +1,142 @@
+/*-
+ * Copyright (c) 2012 Konstantin Belousov <kib@FreeBSD.org>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <sys/cdefs.h>
+__FBSDID("$FreeBSD$");
+
+#include <sys/elf.h>
+#include <sys/time.h>
+#include <sys/vdso.h>
+#include <errno.h>
+#include <time.h>
+#include <machine/atomic.h>
+#include "libc_private.h"
+
+static u_int
+tc_delta(const struct vdso_timehands *th)
+{
+
+	return ((__vdso_gettc(th) - th->th_offset_count) &
+	    th->th_counter_mask);
+}
+
+static int
+binuptime(struct bintime *bt, struct vdso_timekeep *tk, int abs)
+{
+	struct vdso_timehands *th;
+	uint32_t curr, gen;
+
+	do {
+		if (!tk->tk_enabled)
+			return (ENOSYS);
+
+		/*
+		 * XXXKIB. The load of tk->tk_current should use
+		 * atomic_load_acq_32 to provide load barrier. But
+		 * since tk points to r/o mapped page, x86
+		 * implementation of atomic_load_acq faults.
+		 */
+		curr = tk->tk_current;
+		rmb();
+		th = &tk->tk_th[curr];
+		if (th->th_algo != VDSO_TH_ALGO_1)
+			return (ENOSYS);
+		gen = th->th_gen;
+		*bt = th->th_offset;
+		bintime_addx(bt, th->th_scale * tc_delta(th));
+		if (abs)
+			bintime_add(bt, &th->th_boottime);
+
+		/*
+		 * Barrier for load of both tk->tk_current and th->th_gen.
+		 */
+		rmb();
+	} while (curr != tk->tk_current || gen == 0 || gen != th->th_gen);
+	return (0);
+}
+
+static struct vdso_timekeep *tk;
+
+int
+__vdso_gettimeofday(struct timeval *tv, struct timezone *tz)
+{
+	struct bintime bt;
+	int error;
+
+	if (tz != NULL)
+		return (ENOSYS);
+	if (tk == NULL) {
+		error = _elf_aux_info(AT_TIMEKEEP, &tk, sizeof(tk));
+		if (error != 0 || tk == NULL)
+			return (ENOSYS);
+	}
+	if (tk->tk_ver != VDSO_TK_VER_CURR)
+		return (ENOSYS);
+	error = binuptime(&bt, tk, 1);
+	if (error != 0)
+		return (error);
+	bintime2timeval(&bt, tv);
+	return (0);
+}
+
+int
+__vdso_clock_gettime(clockid_t clock_id, struct timespec *ts)
+{
+	struct bintime bt;
+	int abs, error;
+
+	if (tk == NULL) {
+		error = _elf_aux_info(AT_TIMEKEEP, &tk, sizeof(tk));
+		if (error != 0 || tk == NULL)
+			return (ENOSYS);
+	}
+	if (tk->tk_ver != VDSO_TK_VER_CURR)
+		return (ENOSYS);
+	switch (clock_id) {
+	case CLOCK_REALTIME:
+	case CLOCK_REALTIME_PRECISE:
+	case CLOCK_REALTIME_FAST:
+	case CLOCK_SECOND:
+		abs = 1;
+		break;
+	case CLOCK_MONOTONIC:
+	case CLOCK_MONOTONIC_PRECISE:
+	case CLOCK_MONOTONIC_FAST:
+	case CLOCK_UPTIME:
+	case CLOCK_UPTIME_PRECISE:
+	case CLOCK_UPTIME_FAST:
+		abs = 0;
+		break;
+	default:
+		return (ENOSYS);
+	}
+	error = binuptime(&bt, tk, abs);
+	if (error != 0)
+		return (error);
+	bintime2timespec(&bt, ts);
+	if (clock_id == CLOCK_SECOND)
+		ts->tv_nsec = 0;
+	return (0);
+}