| From | Andi Kleen <> | Subject | [PATCH] [105/275] sched: Call tick_check_idle before __irq_enter | Date | Wed, 30 Mar 2011 14:05:44 -0700 (PDT) |
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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 <yong.zhang0@gmail.com> Signed-off-by: Venkatesh Pallipadi <venki@google.com> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Signed-off-by: Andi Kleen <ak@linux.intel.com> LKML-Reference: <1286237003-12406-9-git-send-email-venki@google.com> Signed-off-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Mike Galbraith <efault@gmx.de> Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de> --- 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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