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SubjectRe: [PATCH 02/11] sched, rcu: Make RCU use resched_cpu()
On Mon, Sep 23, 2013 at 09:55:40AM -0700, Paul E. McKenney wrote:
> On Tue, Sep 17, 2013 at 04:40:12PM +0200, Peter Zijlstra wrote:
> > Thomas Meyer reported a UP build fail, should be fixed.
> >
> > ---
> > Subject: sched, rcu: Make RCU use resched_cpu()
> > From: Peter Zijlstra <peterz@infradead.org>
> > Date: Tue Sep 17 09:30:55 CEST 2013
> >
> > We're going to deprecate and remove set_need_resched() for it will do
> > the wrong thing. Make an exception for RCU and allow it to use
> > resched_cpu() which will do the right thing.
> >
> > Cc: Paul McKenney <paulmck@linux.vnet.ibm.com>
> > Signed-off-by: Peter Zijlstra <peterz@infradead.org>
>
> Queued for 3.13, thank you!

Passes light testing, but I am confused about why the change to
resched_task() when only resched_cpu() is invoked elsewhere in the patch.
Enlightenment?

Thanx, Paul

> > ---
> > kernel/rcutree.c | 15 ++++++++++++++-
> > kernel/sched/core.c | 10 ++--------
> > 2 files changed, 16 insertions(+), 9 deletions(-)
> >
> > --- a/kernel/rcutree.c
> > +++ b/kernel/rcutree.c
> > @@ -898,6 +898,12 @@ static void print_other_cpu_stall(struct
> > force_quiescent_state(rsp); /* Kick them all. */
> > }
> >
> > +/*
> > + * This function really isn't for public consumption, but RCU is special in
> > + * that context switches can allow the state machine to make progress.
> > + */
> > +extern void resched_cpu(int cpu);
> > +
> > static void print_cpu_stall(struct rcu_state *rsp)
> > {
> > int cpu;
> > @@ -927,7 +933,14 @@ static void print_cpu_stall(struct rcu_s
> > 3 * rcu_jiffies_till_stall_check() + 3;
> > raw_spin_unlock_irqrestore(&rnp->lock, flags);
> >
> > - set_need_resched(); /* kick ourselves to get things going. */
> > + /*
> > + * Attempt to revive the RCU machinery by forcing a context switch.
> > + *
> > + * A context switch would normally allow the RCU state machine to make
> > + * progress and it could be we're stuck in kernel space without context
> > + * switches for an entirely unreasonable amount of time.
> > + */
> > + resched_cpu(smp_processor_id());
> > }
> >
> > static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp)
> > --- a/kernel/sched/core.c
> > +++ b/kernel/sched/core.c
> > @@ -513,12 +513,11 @@ static inline void init_hrtick(void)
> > * might also involve a cross-CPU call to trigger the scheduler on
> > * the target CPU.
> > */
> > -#ifdef CONFIG_SMP
> > void resched_task(struct task_struct *p)
> > {
> > int cpu;
> >
> > - assert_raw_spin_locked(&task_rq(p)->lock);
> > + lockdep_assert_held(&task_rq(p)->lock);
> >
> > if (test_tsk_need_resched(p))
> > return;
> > @@ -546,6 +545,7 @@ void resched_cpu(int cpu)
> > raw_spin_unlock_irqrestore(&rq->lock, flags);
> > }
> >
> > +#ifdef CONFIG_SMP
> > #ifdef CONFIG_NO_HZ_COMMON
> > /*
> > * In the semi idle case, use the nearest busy cpu for migrating timers
> > @@ -693,12 +693,6 @@ void sched_avg_update(struct rq *rq)
> > }
> > }
> >
> > -#else /* !CONFIG_SMP */
> > -void resched_task(struct task_struct *p)
> > -{
> > - assert_raw_spin_locked(&task_rq(p)->lock);
> > - set_tsk_need_resched(p);
> > -}
> > #endif /* CONFIG_SMP */
> >
> > #if defined(CONFIG_RT_GROUP_SCHED) || (defined(CONFIG_FAIR_GROUP_SCHED) && \
> >
> >



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