[PATCH 13/14] sched/cputime: Handle idle irqtime gracefully

[Frederic Weisbecker <frederic@kernel.org>]

The dyntick-idle cputime accounting always assumes that IRQ time
accounting is enabled and consequently stops elapsing the idle time
during dyntick-idle IRQs.

This doesn't mix up well with disabled IRQ time accounting because then
idle IRQs become a cputime blind-spot. Also this feature is disabled
on most configurations and the overhead of pausing dyntick-idle
accounting while in idle IRQs could then be avoided.

Fix the situation with conditionally pausing dyntick-idle accounting
during idle IRQs only if neither native vtime (which does IRQ time
accounting) nor generic IRQ time accounting are enabled.

Also make sure that the accumulated IRQ time is not accidentally
substracted from later accounting.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Tested-by: Shrikanth Hegde <sshegde@linux.ibm.com>
---
 kernel/sched/cputime.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
index 137e6b099fa9..a77b6f1dbdca 100644
--- a/kernel/sched/cputime.c
+++ b/kernel/sched/cputime.c
@@ -47,7 +47,8 @@ static void irqtime_account_delta(struct irqtime *irqtime, u64 delta,
 	u64_stats_update_begin(&irqtime->sync);
 	cpustat[idx] += delta;
 	irqtime->total += delta;
-	irqtime->tick_delta += delta;
+	if (!kcpustat_idle_dyntick())
+		irqtime->tick_delta += delta;
 	u64_stats_update_end(&irqtime->sync);
 }
 
@@ -478,7 +479,8 @@ void kcpustat_irq_enter(u64 now)
 {
 	struct kernel_cpustat *kc = kcpustat_this_cpu;
 
-	if (!vtime_generic_enabled_this_cpu())
+	if (!vtime_generic_enabled_this_cpu() &&
+	    (irqtime_enabled() || vtime_accounting_enabled_this_cpu()))
 		kcpustat_idle_stop(kc, now);
 }
 
@@ -486,7 +488,8 @@ void kcpustat_irq_exit(u64 now)
 {
 	struct kernel_cpustat *kc = kcpustat_this_cpu;
 
-	if (!vtime_generic_enabled_this_cpu())
+	if (!vtime_generic_enabled_this_cpu() &&
+	    (irqtime_enabled() || vtime_accounting_enabled_this_cpu()))
 		kcpustat_idle_start(kc, now);
 }
 
-- 
2.53.0