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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>
hifive-unleashed-5.1
David Howells 2008-09-24 17:48:31 +01:00 committed by Linus Torvalds
parent b4f151ff89
commit 08ec3c2d45
1 changed files with 41 additions and 11 deletions
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52
arch/mn10300/kernel/time.c
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@ -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 @@ static struct irqaction timer_irq = {
.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 @@ void __init time_init(void)
/* start the watchdog timer */
watchdog_go();
#endif
mn10300_sched_clock_init();
}