From: Daniel Lezcano <daniel.lezcano@linaro.org>
To: tglx@linutronix.de
Cc: linux-kernel@vger.kernel.org, andriy.shevchenko@linux.intel.com
Subject: [PATCH V2 2/9] genirq/timings: Fix timings buffer inspection
Date: Fri, 24 May 2019 13:16:08 +0200 [thread overview]
Message-ID: <20190524111615.4891-3-daniel.lezcano@linaro.org> (raw)
In-Reply-To: <20190524111615.4891-1-daniel.lezcano@linaro.org>
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 <daniel.lezcano@linaro.org>
---
kernel/irq/timings.c | 23 ++++++++++++++++++-----
1 file changed, 18 insertions(+), 5 deletions(-)
diff --git a/kernel/irq/timings.c b/kernel/irq/timings.c
index 60362aca4ca4..250bb00ccd85 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];
@@ -528,11 +545,7 @@ 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)
--
2.17.1
next prev parent reply other threads:[~2019-05-24 11:17 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-24 11:16 [PATCH V2 0/9] genirq/timings: Fixes and selftests Daniel Lezcano
2019-05-24 11:16 ` [PATCH V2 1/9] genirq/timings: Fix next event index function Daniel Lezcano
2019-05-24 13:51 ` Andy Shevchenko
2019-05-24 11:16 ` Daniel Lezcano [this message]
2019-05-24 11:16 ` [PATCH V2 3/9] genirq/timings: Optimize the period detection speed Daniel Lezcano
2019-05-24 11:16 ` [PATCH V2 4/9] genirq/timings: Use the min kernel macro Daniel Lezcano
2019-05-24 13:57 ` Andy Shevchenko
2019-05-24 16:11 ` Daniel Lezcano
2019-05-24 11:16 ` [PATCH V2 5/9] genirq/timings: Encapsulate timings push Daniel Lezcano
2019-05-24 11:16 ` [PATCH V2 6/9] genirq/timings: Encapsulate storing function Daniel Lezcano
2019-05-24 11:16 ` [PATCH V2 7/9] genirq/timings: Add selftest for circular array Daniel Lezcano
2019-05-24 14:00 ` Andy Shevchenko
2019-05-24 16:00 ` Daniel Lezcano
2019-05-24 11:16 ` [PATCH V2 8/9] genirq/timings: Add selftest for irqs circular buffer Daniel Lezcano
2019-05-24 11:16 ` [PATCH V2 9/9] genirq/timings: Add selftest for next event computation Daniel Lezcano
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