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    SubjectRe: [PATCH 03/33] cputime: Generic on-demand virtual cputime accounting
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    On Tue, 2013-01-08 at 03:08 +0100, Frederic Weisbecker wrote:

    > diff --git a/kernel/context_tracking.c b/kernel/context_tracking.c
    > index c952770..bd461ad 100644
    > --- a/kernel/context_tracking.c
    > +++ b/kernel/context_tracking.c
    > @@ -56,7 +56,7 @@ void user_enter(void)
    > local_irq_save(flags);
    > if (__this_cpu_read(context_tracking.active) &&
    > __this_cpu_read(context_tracking.state) != IN_USER) {
    > - __this_cpu_write(context_tracking.state, IN_USER);
    > + vtime_user_enter(current);
    > /*
    > * At this stage, only low level arch entry code remains and
    > * then we'll run in userspace. We can assume there won't be
    > @@ -65,6 +65,7 @@ void user_enter(void)
    > * on the tick.
    > */
    > rcu_user_enter();

    Hmm, the rcu_user_enter() can do quite a bit. Too bad we are accounting
    it as user time. I wonder if we could move the vtime_user_enter() below
    it. But then if vtime_user_enter() calls rcu_read_lock() it breaks.

    The notorious chicken vs egg ordeal!

    -- Steve

    > + __this_cpu_write(context_tracking.state, IN_USER);
    > }
    > local_irq_restore(flags);
    > }
    > @@ -90,12 +91,13 @@ void user_exit(void)
    >
    > local_irq_save(flags);
    > if (__this_cpu_read(context_tracking.state) == IN_USER) {
    > - __this_cpu_write(context_tracking.state, IN_KERNEL);
    > /*
    > * We are going to run code that may use RCU. Inform
    > * RCU core about that (ie: we may need the tick again).
    > */
    > rcu_user_exit();
    > + vtime_user_exit(current);
    > + __this_cpu_write(context_tracking.state, IN_KERNEL);
    > }
    > local_irq_restore(flags);
    > }




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