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authorJohn Stultz <john.stultz@linaro.org>2015-03-11 21:16:31 -0700
committerIngo Molnar <mingo@kernel.org>2015-03-12 10:16:38 +0100
commitfb82fe2fe8588745edd73aa3a6229facac5c1e15 (patch)
tree1ab7c25dfa0e89f83f07fad2a04467d8c7864ebb /kernel/time
parent362fde0410377e468ca00ad363fdf3e3ec42eb6a (diff)
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: 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>
Diffstat (limited to 'kernel/time')
-rw-r--r--kernel/time/clocksource.c28
-rw-r--r--kernel/time/sched_clock.c2
2 files changed, 17 insertions, 13 deletions
diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
index ace95763b3a6..fc2a9de43ca1 100644
--- a/kernel/time/clocksource.c
+++ b/kernel/time/clocksource.c
@@ -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);
diff --git a/kernel/time/sched_clock.c b/kernel/time/sched_clock.c
index 3b8ae45020c1..ca3bc5c7027c 100644
--- a/kernel/time/sched_clock.c
+++ b/kernel/time/sched_clock.c
@@ -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*/