From 2840eef0513c518faeb8a0ab8d07268c6285cdd0 Mon Sep 17 00:00:00 2001 From: Daniel Lezcano Date: Mon, 27 May 2019 22:55:15 +0200 Subject: 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: bbba0e7c5cda "genirq/timings: Add array suffix computation code" Signed-off-by: Daniel Lezcano Signed-off-by: Thomas Gleixner Cc: andriy.shevchenko@linux.intel.com Link: https://lkml.kernel.org/r/20190527205521.12091-3-daniel.lezcano@linaro.org --- kernel/irq/timings.c | 23 ++++++++++++++++++----- 1 file changed, 18 insertions(+), 5 deletions(-) (limited to 'kernel/irq') diff --git a/kernel/irq/timings.c b/kernel/irq/timings.c index 4f5daf3db13b..19d2fad379ee 100644 --- a/kernel/irq/timings.c +++ b/kernel/irq/timings.c @@ -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) -- cgit v1.2.3-59-g8ed1b