Add support for timeconting in userland.

This diff exposes parts of clock_gettime(2) and gettimeofday(2) to
userland via libc eliberating processes from the need for a context
switch everytime they want to count the passage of time.

If a timecounter clock can be exposed to userland than it needs to set
its tc_user member to a non-zero value. Tested with one or multiple
counters per architecture.

The timing data is shared through a pointer found in the new ELF
auxiliary vector AUX_openbsd_timekeep containing timehands information
that is frequently updated by the kernel.

Timing differences between the last kernel update and the current time
are adjusted in userland by the tc_get_timecount() function inside the
MD usertc.c file.

This permits a much more responsive environment, quite visible in
browsers, office programs and gaming (apparently one is are able to fly
in Minecraft now).

Tested by robert@, sthen@, naddy@, kmos@, phessler@, and many others!

OK from at least kettenis@, cheloha@, naddy@, sthen@

1 files changed, 138 insertions, 0 deletions

diff --git a/lib/libc/sys/microtime.c b/lib/libc/sys/microtime.c
new file mode 100644
index 00000000000..e85a86a78de
--- /dev/null
+++ b/lib/libc/sys/microtime.c
@@ -0,0 +1,138 @@
+/*	$OpenBSD: microtime.c,v 1.1 2020/07/06 13:33:06 pirofti Exp $ */
+/*
+ * Copyright (c) 2000 Poul-Henning Kamp <phk@FreeBSD.org>
+ * Copyright (c) 2020 Paul Irofti <paul@irofti.net>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#include <sys/types.h>
+#include <sys/atomic.h>
+#include <sys/timetc.h>
+
+#include <time.h>
+
+/*
+ * Return the difference between the timehands' counter value now and what
+ * was when we copied it to the timehands' offset_count.
+ */
+static inline int
+tc_delta(struct timekeep *tk, u_int *delta)
+{
+	u_int tc;
+
+	if (_tc_get_timecount(tk, &tc))
+		return -1;
+	*delta = (tc - tk->tk_offset_count) & tk->tk_counter_mask;
+	return 0;
+}
+
+static int
+binuptime(struct bintime *bt, struct timekeep *tk)
+{
+	u_int gen, delta;
+
+	do {
+		gen = tk->tk_generation;
+		membar_consumer();
+		*bt = tk->tk_offset;
+		if (tc_delta(tk, &delta))
+			return -1;
+		bintimeaddfrac(bt, tk->tk_scale * delta, bt);
+		membar_consumer();
+	} while (gen == 0 || gen != tk->tk_generation);
+
+	return 0;
+}
+
+static int
+binruntime(struct bintime *bt, struct timekeep *tk)
+{
+	u_int gen, delta;
+
+	do {
+		gen = tk->tk_generation;
+		membar_consumer();
+		if (tc_delta(tk, &delta))
+			return -1;
+		bintimeaddfrac(&tk->tk_offset, tk->tk_scale * delta, bt);
+		bintimesub(bt, &tk->tk_naptime, bt);
+		membar_consumer();
+	} while (gen == 0 || gen != tk->tk_generation);
+
+	return 0;
+}
+
+static int
+bintime(struct bintime *bt, struct timekeep *tk)
+{
+	u_int gen, delta;
+
+	do {
+		gen = tk->tk_generation;
+		membar_consumer();
+		*bt = tk->tk_offset;
+		if (tc_delta(tk, &delta))
+			return -1;
+		bintimeaddfrac(bt, tk->tk_scale * delta, bt);
+		bintimeadd(bt, &tk->tk_boottime, bt);
+		membar_consumer();
+	} while (gen == 0 || gen != tk->tk_generation);
+
+	return 0;
+}
+
+int
+_microtime(struct timeval *tvp, struct timekeep *tk)
+{
+	struct bintime bt;
+
+	if (bintime(&bt, tk))
+		return -1;
+	BINTIME_TO_TIMEVAL(&bt, tvp);
+	return 0;
+}
+
+int
+_nanotime(struct timespec *tsp, struct timekeep *tk)
+{
+	struct bintime bt;
+
+	if (bintime(&bt, tk))
+		return -1;
+	BINTIME_TO_TIMESPEC(&bt, tsp);
+	return 0;
+}
+
+int
+_nanoruntime(struct timespec *ts, struct timekeep *tk)
+{
+	struct bintime bt;
+
+	if (binruntime(&bt, tk))
+		return -1;
+	BINTIME_TO_TIMESPEC(&bt, ts);
+	return 0;
+}
+
+
+int
+_nanouptime(struct timespec *tsp, struct timekeep *tk)
+{
+	struct bintime bt;
+
+	if (binuptime(&bt, tk))
+		return -1;
+	BINTIME_TO_TIMESPEC(&bt, tsp);
+	return 0;
+}