Commit fb82fe2f authored by John Stultz's avatar John Stultz Committed by Ingo Molnar
Browse files

clocksource: Add 'max_cycles' to 'struct clocksource' 



In order to facilitate clocksource validation, add a
'max_cycles' field to the clocksource structure which
will hold the maximum cycle value that can safely be
multiplied without potentially causing an overflow.

Signed-off-by: default avatarJohn Stultz <john.stultz@linaro.org>
Cc: Dave Jones <davej@codemonkey.org.uk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Prarit Bhargava <prarit@redhat.com>
Cc: Richard Cochran <richardcochran@gmail.com>
Cc: Stephen Boyd <sboyd@codeaurora.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1426133800-29329-4-git-send-email-john.stultz@linaro.org


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 362fde04

include/linux/clocksource.h

+3 −2
Original line number Diff line number Diff line
@@ -56,6 +56,7 @@ struct module; 
 * @shift:		cycle to nanosecond divisor (power of two)

 * @max_idle_ns:	max idle time permitted by the clocksource (nsecs)

 * @maxadj:		maximum adjustment value to mult (~11%)

 * @max_cycles:		maximum safe cycle value which won't overflow on multiplication

 * @flags:		flags describing special properties

 * @archdata:		arch-specific data

 * @suspend:		suspend function for the clocksource, if necessary
@@ -76,7 +77,7 @@ struct clocksource { 
#ifdef CONFIG_ARCH_CLOCKSOURCE_DATA

	struct arch_clocksource_data archdata;

#endif



	u64 max_cycles;

	const char *name;

	struct list_head list;

	int rating;
@@ -189,7 +190,7 @@ extern struct clocksource * __init clocksource_default_clock(void); 
extern void clocksource_mark_unstable(struct clocksource *cs);



extern u64

clocks_calc_max_nsecs(u32 mult, u32 shift, u32 maxadj, u64 mask);

clocks_calc_max_nsecs(u32 mult, u32 shift, u32 maxadj, u64 mask, u64 *max_cycles);

extern void

clocks_calc_mult_shift(u32 *mult, u32 *shift, u32 from, u32 to, u32 minsec);

kernel/time/clocksource.c

+16 −12
Original line number Diff line number Diff line
@@ -469,11 +469,13 @@ static u32 clocksource_max_adjustment(struct clocksource *cs) 
 * @shift:	cycle to nanosecond divisor (power of two)

 * @maxadj:	maximum adjustment value to mult (~11%)

 * @mask:	bitmask for two's complement subtraction of non 64 bit counters

 * @max_cyc:	maximum cycle value before potential overflow (does not include

 *		any safety margin)

 *

 * NOTE: This function includes a safety margin of 50%, so that bad clock values

 * can be detected.

 */

u64 clocks_calc_max_nsecs(u32 mult, u32 shift, u32 maxadj, u64 mask)

u64 clocks_calc_max_nsecs(u32 mult, u32 shift, u32 maxadj, u64 mask, u64 *max_cyc)

{

	u64 max_nsecs, max_cycles;
@@ -493,6 +495,10 @@ u64 clocks_calc_max_nsecs(u32 mult, u32 shift, u32 maxadj, u64 mask) 
	max_cycles = min(max_cycles, mask);

	max_nsecs = clocksource_cyc2ns(max_cycles, mult - maxadj, shift);



	/* return the max_cycles value as well if requested */

	if (max_cyc)

		*max_cyc = max_cycles;



	/* Return 50% of the actual maximum, so we can detect bad values */

	max_nsecs >>= 1;
@@ -500,17 +506,15 @@ u64 clocks_calc_max_nsecs(u32 mult, u32 shift, u32 maxadj, u64 mask) 
}



/**

 * clocksource_max_deferment - Returns max time the clocksource should be deferred

 * @cs:         Pointer to clocksource

 * clocksource_update_max_deferment - Updates the clocksource max_idle_ns & max_cycles

 * @cs:         Pointer to clocksource to be updated

 *

 */

static u64 clocksource_max_deferment(struct clocksource *cs)

static inline void clocksource_update_max_deferment(struct clocksource *cs)

{

	u64 max_nsecs;



	max_nsecs = clocks_calc_max_nsecs(cs->mult, cs->shift, cs->maxadj,

					  cs->mask);

	return max_nsecs;

	cs->max_idle_ns = clocks_calc_max_nsecs(cs->mult, cs->shift,

						cs->maxadj, cs->mask,

						&cs->max_cycles);

}



#ifndef CONFIG_ARCH_USES_GETTIMEOFFSET
@@ -684,7 +688,7 @@ void __clocksource_updatefreq_scale(struct clocksource *cs, u32 scale, u32 freq) 
		cs->maxadj = clocksource_max_adjustment(cs);

	}



	cs->max_idle_ns = clocksource_max_deferment(cs);

	clocksource_update_max_deferment(cs);

}

EXPORT_SYMBOL_GPL(__clocksource_updatefreq_scale);
@@ -730,8 +734,8 @@ int clocksource_register(struct clocksource *cs) 
		"Clocksource %s might overflow on 11%% adjustment\n",

		cs->name);



	/* calculate max idle time permitted for this clocksource */

	cs->max_idle_ns = clocksource_max_deferment(cs);

	/* Update max idle time permitted for this clocksource */

	clocksource_update_max_deferment(cs);



	mutex_lock(&clocksource_mutex);

	clocksource_enqueue(cs);

kernel/time/sched_clock.c

+1 −1
Original line number Diff line number Diff line
@@ -126,7 +126,7 @@ void __init sched_clock_register(u64 (*read)(void), int bits, 
	new_mask = CLOCKSOURCE_MASK(bits);



	/* calculate how many nanosecs until we risk wrapping */

	wrap = clocks_calc_max_nsecs(new_mult, new_shift, 0, new_mask);

	wrap = clocks_calc_max_nsecs(new_mult, new_shift, 0, new_mask, NULL);

	new_wrap_kt = ns_to_ktime(wrap);



	/* update epoch for new counter and update epoch_ns from old counter*/

CRA Git | Maintained and supported by SUSTech CRA and CCSE