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Commit 08ec3c2d authored by David Howells's avatar David Howells Committed by Linus Torvalds
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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: default avatarDavid Howells <dhowells@redhat.com>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent b4f151ff

arch/mn10300/kernel/time.c

+41 −11
Original line number Diff line number Diff line 
/* 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 */



	/* read the TSC value

	 */

	tsc = 0 - get_cycles(); /* get_cycles() counts down */



	quot.w[0] = mn10300_last_tsc - get_cycles();

	quot.w[1] = 1000000000;

	/* 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;



	asm("mulu %2,%3,%0,%1"

	    : "=r"(quot.w[1]), "=r"(quot.w[0])

	    : "0"(quot.w[1]), "1"(quot.w[0])

	/* 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();

}