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plan9: nanosec: fall back to nsec() in case cycle is unusable

--- a/plan9.c

+++ b/plan9.c

@@ -361,7 +361,8 @@

 /*

  * nsec() is wallclock and can be adjusted by timesync

- * so need to use cycles() instead

+ * so need to use cycles() instead, but fall back to

+ * nsec() in case we can't

  *

  * "fasthz" is how many ticks there are in a second

  * can be read from /dev/time

@@ -376,20 +377,28 @@

 	int f, n, i;

 	char tmp[128], *e;

-	if (fasthz < 1) {

-		if ((f = open("/dev/time", OREAD)) < 0)

-			sysfatal("failed to open /dev/time");

-		if ((n = read(f, tmp, sizeof(tmp)-1)) < 2)

-			sysfatal("failed to read /dev/time");

-		tmp[n] = 0;

-		e = tmp;

-		for (i = 0; i < 3; i++)

-			strtoll(e, &e, 10);

-		fasthz = strtoll(e, nil, 10);

-		if (fasthz < 1)

-			sysfatal("failed to read or invalid fasthz");

-		close(f);

-		cycles(&xstart);

+	if (fasthz == ~0ULL)

+		return nsec() - xstart;

+

+	if (fasthz == 0) {

+		fasthz = ~0ULL;

+		if ((f = open("/dev/time", OREAD)) >= 0 && (n = read(f, tmp, sizeof(tmp)-1)) > 2) {

+			tmp[n] = 0;

+			e = tmp;

+			for (i = 0; i < 3; i++)

+				strtoll(e, &e, 10);

+			fasthz = strtoll(e, nil, 10);

+			if (fasthz < 1)

+				fasthz = ~0ULL;

+			close(f);

+			cycles(&xstart);

+		}

+		if (fasthz == ~0ULL) {

+			fprint(2, "couldn't get fasthz, falling back to nsec()\n");

+			fprint(2, "you might want to disable aux/timesync\n");

+			xstart = nsec();

+			return 0;

+		}

 	}

 	cycles(&x);

 	if (x < xstart) { /* wrap around */

@@ -441,9 +450,7 @@

 			else if (end - n > 25000000LL)

 				sleep(20);

 			else if (end - n > 10000000LL)

-				sleep((end - n) / 1000000LL);

-			else

-				yield();

+				sleep(1);

 		} while (!forward);

 		framedev = (processnew - processold - 15000000000LL/bpm)/1000000LL;