MN10300: Make sched_clock() report time since boot
Make sched_clock() report time since boot rather than time since last
timer interrupt.
Make sched_clock() expand and scale the 32-bit TSC value running at
IOCLK speed (~33MHz) to a 64-bit nanosecond counter, using cnt32_to_63()
acquired from the ARM arch and without using slow DIVU instructions
every call.
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/arch/mn10300/kernel/time.c b/arch/mn10300/kernel/time.c
index babb7c2..e460658 100644
--- a/arch/mn10300/kernel/time.c
+++ b/arch/mn10300/kernel/time.c
@@ -1,6 +1,6 @@
/* MN10300 Low level time management
*
- * Copyright (C) 2007 Red Hat, Inc. All Rights Reserved.
+ * Copyright (C) 2007-2008 Red Hat, Inc. All Rights Reserved.
* Written by David Howells (dhowells@redhat.com)
* - Derived from arch/i386/kernel/time.c
*
@@ -16,6 +16,7 @@
#include <linux/init.h>
#include <linux/smp.h>
#include <linux/profile.h>
+#include <linux/cnt32_to_63.h>
#include <asm/irq.h>
#include <asm/div64.h>
#include <asm/processor.h>
@@ -40,27 +41,54 @@
.name = "timer",
};
+static unsigned long sched_clock_multiplier;
+
/*
* scheduler clock - returns current time in nanosec units.
*/
unsigned long long sched_clock(void)
{
union {
- unsigned long long l;
- u32 w[2];
- } quot;
+ unsigned long long ll;
+ unsigned l[2];
+ } tsc64, result;
+ unsigned long tsc, tmp;
+ unsigned product[3]; /* 96-bit intermediate value */
- quot.w[0] = mn10300_last_tsc - get_cycles();
- quot.w[1] = 1000000000;
+ /* read the TSC value
+ */
+ tsc = 0 - get_cycles(); /* get_cycles() counts down */
- asm("mulu %2,%3,%0,%1"
- : "=r"(quot.w[1]), "=r"(quot.w[0])
- : "0"(quot.w[1]), "1"(quot.w[0])
+ /* expand to 64-bits.
+ * - sched_clock() must be called once a minute or better or the
+ * following will go horribly wrong - see cnt32_to_63()
+ */
+ tsc64.ll = cnt32_to_63(tsc) & 0x7fffffffffffffffULL;
+
+ /* scale the 64-bit TSC value to a nanosecond value via a 96-bit
+ * intermediate
+ */
+ asm("mulu %2,%0,%3,%0 \n" /* LSW * mult -> 0:%3:%0 */
+ "mulu %2,%1,%2,%1 \n" /* MSW * mult -> %2:%1:0 */
+ "add %3,%1 \n"
+ "addc 0,%2 \n" /* result in %2:%1:%0 */
+ : "=r"(product[0]), "=r"(product[1]), "=r"(product[2]), "=r"(tmp)
+ : "0"(tsc64.l[0]), "1"(tsc64.l[1]), "2"(sched_clock_multiplier)
: "cc");
- do_div(quot.l, MN10300_TSCCLK);
+ result.l[0] = product[1] << 16 | product[0] >> 16;
+ result.l[1] = product[2] << 16 | product[1] >> 16;
- return quot.l;
+ return result.ll;
+}
+
+/*
+ * initialise the scheduler clock
+ */
+static void __init mn10300_sched_clock_init(void)
+{
+ sched_clock_multiplier =
+ __muldiv64u(NSEC_PER_SEC, 1 << 16, MN10300_TSCCLK);
}
/*
@@ -128,4 +156,6 @@
/* start the watchdog timer */
watchdog_go();
#endif
+
+ mn10300_sched_clock_init();
}
