Messages in this thread | | | Subject | Re: [RFC][PATCH 11/18] sched: Add p->pi_lock to task_rq_lock() | From | Peter Zijlstra <> | Date | Thu, 03 Feb 2011 18:16:50 +0100 |
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On Fri, 2011-01-28 at 16:21 -0800, Frank Rowand wrote: > On 01/04/11 06:59, Peter Zijlstra wrote: > > In order to be able to call set_task_cpu() while either holding > > p->pi_lock or task_rq(p)->lock we need to hold both locks in order to > > stabilize task_rq(). > > > > This makes task_rq_lock() acquire both locks, and have > > __task_rq_lock() validate that p->pi_lock is held. This increases the > > locking overhead for most scheduler syscalls but allows reduction of > > rq->lock contention for some scheduler hot paths (ttwu). > > > > Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> > > --- > > kernel/sched.c | 81 ++++++++++++++++++++++++++------------------------------- > > 1 file changed, 37 insertions(+), 44 deletions(-) > > > > Index: linux-2.6/kernel/sched.c > > =================================================================== > > > > > @@ -980,10 +972,13 @@ static void __task_rq_unlock(struct rq * > > raw_spin_unlock(&rq->lock); > > } > > > > -static inline void task_rq_unlock(struct rq *rq, unsigned long *flags) > > +static inline void > > +task_rq_unlock(struct rq *rq, struct task_struct *p, unsigned long *flags) > > __releases(rq->lock) > > + __releases(p->pi_lock) > > { > > - raw_spin_unlock_irqrestore(&rq->lock, *flags); > > + raw_spin_unlock(&rq->lock); > > + raw_spin_unlock_irqrestore(&p->pi_lock, *flags); > > } > > > > /* > > Most of the callers of task_rq_unlock() were also fixed up to reflect > the newly added parameter "*p", but a couple were missed. By the end > of the patch series that is ok because the couple that were missed > get removed in patches 12 and 13. But if you want the patch series > to be bisectable (which I think it is otherwise), you might want to > fix those last couple of callers of task_rq_unlock() in this patch.
Fixed those up indeed, thanks!
> > > @@ -2646,9 +2647,9 @@ void sched_fork(struct task_struct *p, i > > * > > * Silence PROVE_RCU. > > */ > > - rcu_read_lock(); > > + raw_spin_lock_irqsave(&p->pi_lock, flags); > > set_task_cpu(p, cpu); > > - rcu_read_unlock(); > > + raw_spin_unlock_irqrestore(&p->pi_lock, flags); > > Does "* Silence PROVE_RCU." no longer apply after remove rcu_read_lock() and > rcu_read_unlock()?
I think the locking is still strictly superfluous, I can't seem to recollect why I changed it from RCU to pi_lock, but since the task is fresh and unhashed it really cannot be subject to concurrency.
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