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clocksource: Add 'max_cycles' to 'struct clocksource'

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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: John 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: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
John Stultz 2015-03-11 21:16:31 -07:00 committed by Ingo Molnar
parent 362fde0410
commit fb82fe2fe8
3 changed files with 20 additions and 15 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
include/linux/clocksource.h
View File

@ -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);

28
kernel/time/clocksource.c
View File

@ -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);

2
kernel/time/sched_clock.c
View File

@ -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*/