diff options
Diffstat (limited to 'kernel/irq/timings.c')
| -rw-r--r-- | kernel/irq/timings.c | 252 |
1 files changed, 2 insertions, 250 deletions
diff --git a/kernel/irq/timings.c b/kernel/irq/timings.c index 1e4cb63a5c82..3cde046a2bc8 100644 --- a/kernel/irq/timings.c +++ b/kernel/irq/timings.c @@ -8,7 +8,6 @@ #include <linux/interrupt.h> #include <linux/idr.h> #include <linux/irq.h> -#include <linux/math64.h> #include <trace/events/irq.h> @@ -19,13 +18,7 @@ DEFINE_STATIC_KEY_FALSE(irq_timing_enabled); DEFINE_PER_CPU(struct irq_timings, irq_timings); struct irqt_stat { - u64 next_evt; - u64 last_ts; - u64 variance; - u32 avg; - u32 nr_samples; - int anomalies; - int valid; + u64 next_evt; }; static DEFINE_IDR(irqt_stats); @@ -41,184 +34,6 @@ void irq_timings_disable(void) } /** - * irqs_update - update the irq timing statistics with a new timestamp - * - * @irqs: an irqt_stat struct pointer - * @ts: the new timestamp - * - * The statistics are computed online, in other words, the code is - * designed to compute the statistics on a stream of values rather - * than doing multiple passes on the values to compute the average, - * then the variance. The integer division introduces a loss of - * precision but with an acceptable error margin regarding the results - * we would have with the double floating precision: we are dealing - * with nanosec, so big numbers, consequently the mantisse is - * negligeable, especially when converting the time in usec - * afterwards. - * - * The computation happens at idle time. When the CPU is not idle, the - * interrupts' timestamps are stored in the circular buffer, when the - * CPU goes idle and this routine is called, all the buffer's values - * are injected in the statistical model continuying to extend the - * statistics from the previous busy-idle cycle. - * - * The observations showed a device will trigger a burst of periodic - * interrupts followed by one or two peaks of longer time, for - * instance when a SD card device flushes its cache, then the periodic - * intervals occur again. A one second inactivity period resets the - * stats, that gives us the certitude the statistical values won't - * exceed 1x10^9, thus the computation won't overflow. - * - * Basically, the purpose of the algorithm is to watch the periodic - * interrupts and eliminate the peaks. - * - * An interrupt is considered periodically stable if the interval of - * its occurences follow the normal distribution, thus the values - * comply with: - * - * avg - 3 x stddev < value < avg + 3 x stddev - * - * Which can be simplified to: - * - * -3 x stddev < value - avg < 3 x stddev - * - * abs(value - avg) < 3 x stddev - * - * In order to save a costly square root computation, we use the - * variance. For the record, stddev = sqrt(variance). The equation - * above becomes: - * - * abs(value - avg) < 3 x sqrt(variance) - * - * And finally we square it: - * - * (value - avg) ^ 2 < (3 x sqrt(variance)) ^ 2 - * - * (value - avg) x (value - avg) < 9 x variance - * - * Statistically speaking, any values out of this interval is - * considered as an anomaly and is discarded. However, a normal - * distribution appears when the number of samples is 30 (it is the - * rule of thumb in statistics, cf. "30 samples" on Internet). When - * there are three consecutive anomalies, the statistics are resetted. - * - */ -static void irqs_update(struct irqt_stat *irqs, u64 ts) -{ - u64 old_ts = irqs->last_ts; - u64 variance = 0; - u64 interval; - s64 diff; - - /* - * The timestamps are absolute time values, we need to compute - * the timing interval between two interrupts. - */ - irqs->last_ts = ts; - - /* - * The interval type is u64 in order to deal with the same - * type in our computation, that prevent mindfuck issues with - * overflow, sign and division. - */ - interval = ts - old_ts; - - /* - * The interrupt triggered more than one second apart, that - * ends the sequence as predictible for our purpose. In this - * case, assume we have the beginning of a sequence and the - * timestamp is the first value. As it is impossible to - * predict anything at this point, return. - * - * Note the first timestamp of the sequence will always fall - * in this test because the old_ts is zero. That is what we - * want as we need another timestamp to compute an interval. - */ - if (interval >= NSEC_PER_SEC) { - memset(irqs, 0, sizeof(*irqs)); - irqs->last_ts = ts; - return; - } - - /* - * Pre-compute the delta with the average as the result is - * used several times in this function. - */ - diff = interval - irqs->avg; - - /* - * Increment the number of samples. - */ - irqs->nr_samples++; - - /* - * Online variance divided by the number of elements if there - * is more than one sample. Normally the formula is division - * by nr_samples - 1 but we assume the number of element will be - * more than 32 and dividing by 32 instead of 31 is enough - * precise. - */ - if (likely(irqs->nr_samples > 1)) - variance = irqs->variance >> IRQ_TIMINGS_SHIFT; - - /* - * The rule of thumb in statistics for the normal distribution - * is having at least 30 samples in order to have the model to - * apply. Values outside the interval are considered as an - * anomaly. - */ - if ((irqs->nr_samples >= 30) && ((diff * diff) > (9 * variance))) { - /* - * After three consecutive anomalies, we reset the - * stats as it is no longer stable enough. - */ - if (irqs->anomalies++ >= 3) { - memset(irqs, 0, sizeof(*irqs)); - irqs->last_ts = ts; - return; - } - } else { - /* - * The anomalies must be consecutives, so at this - * point, we reset the anomalies counter. - */ - irqs->anomalies = 0; - } - - /* - * The interrupt is considered stable enough to try to predict - * the next event on it. - */ - irqs->valid = 1; - - /* - * Online average algorithm: - * - * new_average = average + ((value - average) / count) - * - * The variance computation depends on the new average - * to be computed here first. - * - */ - irqs->avg = irqs->avg + (diff >> IRQ_TIMINGS_SHIFT); - - /* - * Online variance algorithm: - * - * new_variance = variance + (value - average) x (value - new_average) - * - * Warning: irqs->avg is updated with the line above, hence - * 'interval - irqs->avg' is no longer equal to 'diff' - */ - irqs->variance = irqs->variance + (diff * (interval - irqs->avg)); - - /* - * Update the next event - */ - irqs->next_evt = ts + irqs->avg; -} - -/** * irq_timings_next_event - Return when the next event is supposed to arrive * * During the last busy cycle, the number of interrupts is incremented @@ -246,12 +61,6 @@ static void irqs_update(struct irqt_stat *irqs, u64 ts) */ u64 irq_timings_next_event(u64 now) { - struct irq_timings *irqts = this_cpu_ptr(&irq_timings); - struct irqt_stat *irqs; - struct irqt_stat __percpu *s; - u64 ts, next_evt = U64_MAX; - int i, irq = 0; - /* * This function must be called with the local irq disabled in * order to prevent the timings circular buffer to be updated @@ -259,64 +68,7 @@ u64 irq_timings_next_event(u64 now) */ lockdep_assert_irqs_disabled(); - /* - * 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. - * - * Inject measured irq/timestamp to the statistical model - * while decrementing the counter because we consume the data - * from our circular buffer. - */ - for (i = irqts->count & IRQ_TIMINGS_MASK, - irqts->count = min(IRQ_TIMINGS_SIZE, irqts->count); - irqts->count > 0; irqts->count--, i = (i + 1) & IRQ_TIMINGS_MASK) { - - irq = irq_timing_decode(irqts->values[i], &ts); - - s = idr_find(&irqt_stats, irq); - if (s) { - irqs = this_cpu_ptr(s); - irqs_update(irqs, ts); - } - } - - /* - * Look in the list of interrupts' statistics, the earliest - * next event. - */ - idr_for_each_entry(&irqt_stats, s, i) { - - irqs = this_cpu_ptr(s); - - if (!irqs->valid) - continue; - - if (irqs->next_evt <= now) { - irq = i; - next_evt = now; - - /* - * This interrupt mustn't use in the future - * until new events occur and update the - * statistics. - */ - irqs->valid = 0; - break; - } - - if (irqs->next_evt < next_evt) { - irq = i; - next_evt = irqs->next_evt; - } - } - - return next_evt; + return 0; } void irq_timings_free(int irq) |