kunit: irq: Continue increasing hrtimer interval for longer

Currently, kunit_irq_test_timer_func() stops increasing the hrtimer interval as soon as some forward progress is made in each of softirq and task context. Update it to use a more aggressive strategy: increase the interval as long as the hrtimer is running significantly faster than either context.

This resolves an occasional hang in the CRC and crypto library tests under qemu-system-s390x. It was exposed by the change in the default preemption model on s390 from NONE to LAZY. That seems to have exposed the issue by allowing some forward progress to be made while the actual system timer tick is still starved, preventing jiffies from increasing or the task context from making much progress towards max_iterations.

Fixes 201ceb94aa1d ("kunit: irq: Ensure timer doesn't fire too frequently")

Cc [email protected]

Signed-off-by Eric Biggers <[email protected]>

---

This patch is targeting libcrypto-next

 include/kunit/run-in-irq-context.h | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

include/kunit/run-in-irq-context.h +6 -4

index bfe60d6cf28d..3802b6fb218e 100644
@@ -38,11 +38,13 @@ static enum hrtimer_restart 
 kunit_irq_test_timer_func(struct hrtimer *timer)
 	softirq_calls = atomic_read(&state->softirq_func_calls);
 
 	/*
-	 * If the timer is firing too often for the softirq or task to ever have
-	 * a chance to run, increase the timer interval.  This is needed on very
-	 * slow systems.
+	 * If the hrtimer is running much faster than the bh_work or the task,
+	 * then it is firing too fast and might be starving those contexts as
+	 * well as the actual system timer tick.  Increase the interval.
 	 */
-	if (hardirq_calls >= 20 && (softirq_calls == 0 || task_calls == 0))
+	if (hardirq_calls >= 20 &&
+	    (hardirq_calls / 2 > softirq_calls ||
+	     hardirq_calls / 2 > task_calls))
 		state->interval = ktime_add_ns(state->interval, 250);
 

if (!state->func(state->test_specific_state))

Currently, kunit_irq_test_timer_func() stops increasing the hrtimer interval as soon as some forward progress is made in each of softirq and task context. Update it to use a more aggressive strategy: increase the interval as long as the hrtimer is running significantly faster than either context.

This resolves an occasional hang in the CRC and crypto library tests under qemu-system-s390x. It was exposed by the change in the default preemption model on s390 from NONE to LAZY. That seems to have exposed the issue by allowing some forward progress to be made while the actual system timer tick is still starved, preventing jiffies from increasing or the task context from making much progress towards max_iterations.

Fixes 201ceb94aa1d ("kunit: irq: Ensure timer doesn't fire too frequently")

Cc [email protected]

Signed-off-by Eric Biggers <[email protected]>

---

This patch is targeting libcrypto-next

  include/kunit/run-in-irq-context.h | 10 ++++++----
  1 file changed, 6 insertions(+), 4 deletions(-)

include/kunit/run-in-irq-context.h +6 -4

index bfe60d6cf28d..3802b6fb218e 100644
@@ -38,11 +38,13 @@ static enum hrtimer_restart kunit_irq_test_timer_func(struct hrtimer *timer)
  	softirq_calls = atomic_read(&state->softirq_func_calls);
 
  	/*
-	 * If the timer is firing too often for the softirq or task to ever have
-	 * a chance to run, increase the timer interval.  This is needed on very
-	 * slow systems.
+	 * If the hrtimer is running much faster than the bh_work or the task,
+	 * then it is firing too fast and might be starving those contexts as
+	 * well as the actual system timer tick.  Increase the interval.
  	 */
-	if (hardirq_calls >= 20 && (softirq_calls == 0 || task_calls == 0))
+	if (hardirq_calls >= 20 &&
+	    (hardirq_calls / 2 > softirq_calls ||
+	     hardirq_calls / 2 > task_calls))
  		state->interval = ktime_add_ns(state->interval, 250);
 
  	if (!state->func(state->test_specific_state))

base-commit: 6d22ec26295c1412d765e3d687e46224fc332928

Currently, kunit_irq_test_timer_func() stops increasing the hrtimer interval as soon as some forward progress is made in each of softirq and task context. Update it to use a more aggressive strategy: increase the interval as long as the hrtimer is running significantly faster than either context.

This resolves an occasional hang in the CRC and crypto library tests under qemu-system-s390x. It was exposed by the change in the default preemption model on s390 from NONE to LAZY. That seems to have exposed the issue by allowing some forward progress to be made while the actual system timer tick is still starved, preventing jiffies from increasing or the task context from making much progress towards max_iterations.

Fixes 201ceb94aa1d ("kunit: irq: Ensure timer doesn't fire too frequently")

Cc [email protected]

Signed-off-by Eric Biggers <[email protected]>

---

This patch is targeting libcrypto-next