2.6.35-longterm review patch. If anyone has any objections, please let me know.
------------------
Commit: d267f87fb8179c6dba03d08b91952e81bc3723c7 upstream
When CPU is idle and on first interrupt, irq_enter calls tick_check_idle()
to notify interruption from idle. But, there is a problem if this call
is done after __irq_enter, as all routines in __irq_enter may find
stale time due to yet to be done tick_check_idle.
Specifically, trace calls in __irq_enter when they use global clock and also
account_system_vtime change in this patch as it wants to use sched_clock_cpu()
to do proper irq timing.
But, tick_check_idle was moved after __irq_enter intentionally to
prevent problem of unneeded ksoftirqd wakeups by the commit ee5f80a:
irq: call __irq_enter() before calling the tick_idle_check
Impact: avoid spurious ksoftirqd wakeups
Moving tick_check_idle() before __irq_enter and wrapping it with
local_bh_enable/disable would solve both the problems.
Fixed-by: Yong Zhang <[email protected]>
Signed-off-by: Venkatesh Pallipadi <[email protected]>
Signed-off-by: Peter Zijlstra <[email protected]>
Signed-off-by: Andi Kleen <[email protected]>
LKML-Reference: <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
Signed-off-by: Mike Galbraith <[email protected]>
Acked-by: Peter Zijlstra <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
kernel/sched.c | 2 +-
kernel/softirq.c | 12 +++++++++---
2 files changed, 10 insertions(+), 4 deletions(-)
Index: linux-2.6.35.y/kernel/sched.c
===================================================================
--- linux-2.6.35.y.orig/kernel/sched.c 2011-03-29 23:03:00.344291360 -0700
+++ linux-2.6.35.y/kernel/sched.c 2011-03-29 23:54:58.516505136 -0700
@@ -1884,8 +1884,8 @@
local_irq_save(flags);
- now = sched_clock();
cpu = smp_processor_id();
+ now = sched_clock_cpu(cpu);
delta = now - per_cpu(irq_start_time, cpu);
per_cpu(irq_start_time, cpu) = now;
/*
Index: linux-2.6.35.y/kernel/softirq.c
===================================================================
--- linux-2.6.35.y.orig/kernel/softirq.c 2011-03-29 23:03:00.249293792
-0700
+++ linux-2.6.35.y/kernel/softirq.c 2011-03-29 23:03:00.370290694 -0700
@@ -296,10 +296,16 @@
rcu_irq_enter();
if (idle_cpu(cpu) && !in_interrupt()) {
- __irq_enter();
+ /*
+ * Prevent raise_softirq from needlessly waking up ksoftirqd
+ * here, as softirq will be serviced on return from interrupt.
+ */
+ local_bh_disable();
tick_check_idle(cpu);
- } else
- __irq_enter();
+ _local_bh_enable();
+ }
+
+ __irq_enter();
}
#ifdef __ARCH_IRQ_EXIT_IRQS_DISABLED
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