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Commit 2840eef0 authored by Daniel Lezcano's avatar Daniel Lezcano Committed by Thomas Gleixner
Browse files

genirq/timings: Fix timings buffer inspection 



It appears the index beginning computation is not correct, the current
code does:

     i = (irqts->count & IRQ_TIMINGS_MASK) - 1

If irqts->count is equal to zero, we end up with an index equal to -1,
but that does not happen because the function checks against zero
before and returns in such case.

However, if irqts->count is a multiple of IRQ_TIMINGS_SIZE, the
resulting & bit op will be zero and leads also to a -1 index.

Re-introduce the iteration loop belonging to the previous variance
code which was correct.

Fixes: bbba0e7c "genirq/timings: Add array suffix computation code"
Signed-off-by: default avatarDaniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Cc: andriy.shevchenko@linux.intel.com
Link: https://lkml.kernel.org/r/20190527205521.12091-3-daniel.lezcano@linaro.org
parent 619c1baa

kernel/irq/timings.c

+18 −5
Original line number Diff line number Diff line
@@ -267,6 +267,23 @@ void irq_timings_disable(void) 
#define PREDICTION_MAX		10 /* 2 ^ PREDICTION_MAX useconds */

#define PREDICTION_BUFFER_SIZE	16 /* slots for EMAs, hardly more than 16 */



/*

 * Number of elements in the circular buffer: If it happens it was

 * flushed before, then the number of elements could be smaller than

 * IRQ_TIMINGS_SIZE, so the count is used, otherwise the array size is

 * used as we wrapped. The index begins from zero when we did not

 * wrap. That could be done in a nicer way with the proper circular

 * array structure type but with the cost of extra computation in the

 * interrupt handler hot path. We choose efficiency.

 */

#define for_each_irqts(i, irqts)					\

	for (i = irqts->count < IRQ_TIMINGS_SIZE ?			\

		     0 : irqts->count & IRQ_TIMINGS_MASK,		\

		     irqts->count = min(IRQ_TIMINGS_SIZE,		\

					irqts->count);			\

	     irqts->count > 0; irqts->count--,				\

		     i = (i + 1) & IRQ_TIMINGS_MASK)



struct irqt_stat {

	u64	last_ts;

	u64	ema_time[PREDICTION_BUFFER_SIZE];
@@ -526,11 +543,7 @@ u64 irq_timings_next_event(u64 now) 
	 * model while decrementing the counter because we consume the

	 * data from our circular buffer.

	 */



	i = (irqts->count & IRQ_TIMINGS_MASK) - 1;

	irqts->count = min(IRQ_TIMINGS_SIZE, irqts->count);



	for (; irqts->count > 0; irqts->count--, i = (i + 1) & IRQ_TIMINGS_MASK) {

	for_each_irqts(i, irqts) {

		irq = irq_timing_decode(irqts->values[i], &ts);

		s = idr_find(&irqt_stats, irq);

		if (s)