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Commit 749dc6f2 authored by Chris Metcalf's avatar Chris Metcalf
Browse files

arch/tile: Use separate, better minsec values for clocksource and sched_clock. 



We were using the same 5-sec minsec for the clocksource and sched_clock
that we were using for the clock_event_device.  For the clock_event_device
that's exactly right since it has a short maximum countdown time.
But for sched_clock we want to avoid wraparound when converting from
ticks to nsec over a much longer window, so we force a shift of 10.
And for clocksource it seems dodgy to use a 5-sec minsec as well, so we
copy some other platforms and force a shift of 22.

Signed-off-by: default avatarChris Metcalf <cmetcalf@tilera.com>
parent bc63de7c

arch/tile/kernel/time.c

+19 −14
Original line number Diff line number Diff line
@@ -36,16 +36,6 @@ 
/* How many cycles per second we are running at. */

static cycles_t cycles_per_sec __write_once;



/*

 * We set up shift and multiply values with a minsec of five seconds,

 * since our timer counter counts down 31 bits at a frequency of

 * no less than 500 MHz.  See @minsec for clocks_calc_mult_shift().

 * We could use a different value for the 64-bit free-running

 * cycle counter, but we use the same one for consistency, and since

 * we will be reasonably precise with this value anyway.

 */

#define TILE_MINSEC 5



cycles_t get_clock_rate(void)

{

	return cycles_per_sec;
@@ -68,6 +58,14 @@ cycles_t get_cycles(void) 
}

#endif



/*

 * We use a relatively small shift value so that sched_clock()

 * won't wrap around very often.

 */

#define SCHED_CLOCK_SHIFT 10



static unsigned long sched_clock_mult __write_once;



static cycles_t clocksource_get_cycles(struct clocksource *cs)

{

	return get_cycles();
@@ -78,6 +76,7 @@ static struct clocksource cycle_counter_cs = { 
	.rating = 300,

	.read = clocksource_get_cycles,

	.mask = CLOCKSOURCE_MASK(64),

	.shift = 22,   /* typical value, e.g. x86 tsc uses this */

	.flags = CLOCK_SOURCE_IS_CONTINUOUS,

};
@@ -88,8 +87,10 @@ static struct clocksource cycle_counter_cs = { 
void __init setup_clock(void)

{

	cycles_per_sec = hv_sysconf(HV_SYSCONF_CPU_SPEED);

	clocksource_calc_mult_shift(&cycle_counter_cs, cycles_per_sec,

				    TILE_MINSEC);

	sched_clock_mult =

		clocksource_hz2mult(cycles_per_sec, SCHED_CLOCK_SHIFT);

	cycle_counter_cs.mult =

		clocksource_hz2mult(cycles_per_sec, cycle_counter_cs.shift);

}



void __init calibrate_delay(void)
@@ -117,9 +118,14 @@ void __init time_init(void) 
 * counter, plus bit 31, which signifies that the counter has wrapped

 * from zero to (2**31) - 1.  The INT_TILE_TIMER interrupt will be

 * raised as long as bit 31 is set.

 *

 * The TILE_MINSEC value represents the largest range of real-time

 * we can possibly cover with the timer, based on MAX_TICK combined

 * with the slowest reasonable clock rate we might run at.

 */



#define MAX_TICK 0x7fffffff   /* we have 31 bits of countdown timer */

#define TILE_MINSEC 5         /* timer covers no more than 5 seconds */



static int tile_timer_set_next_event(unsigned long ticks,

				     struct clock_event_device *evt)
@@ -211,8 +217,7 @@ void do_timer_interrupt(struct pt_regs *regs, int fault_num) 
unsigned long long sched_clock(void)

{

	return clocksource_cyc2ns(get_cycles(),

				  cycle_counter_cs.mult,

				  cycle_counter_cs.shift);

				  sched_clock_mult, SCHED_CLOCK_SHIFT);

}



int setup_profiling_timer(unsigned int multiplier)