On Wed, Oct 02, 2013 at 05:49:01PM +0200, Oleg Nesterov wrote:
> On 10/02, Peter Zijlstra wrote:
> >
> > From: Oleg Nesterov <o...@redhat.com>
>
> Thanks! I was writing the patch, and I chose almost the same naming ;)
>
> > Signed-off-by: Peter Zijlstra <pet...@infradead.org>
>
> Signed-off-by: Oleg Nesterov <o...@redhat.com>
>
> In fact I'd like to add my sob to 1/3 and 3/3 as well.
>
>
> Paul, to remind, this is only the first step. I am going to send
> the following improvements:
>
> 1. Add rcu_sync->exlusive. The change is simple, just we
> need s/wait_queue_head_t/completion/ in rcu_sync_struct
> and a couple of "if (rss->exclusive)" checks in enter/exit.
>
> 2. rcu_sync_enter() should return !!need_sync. This can help
> in exclusive mode.
>
> 3. rcu_sync_struct needs more function pointers (perhaps we
> should add a single rcu_sync_struct->ops pointer but this
> is minor). See below.
>
> But let me repeat just in case, we should do this later.
> And once this series is applied, I'll change percpu_rw_semaphore.
I took this into account in my review, the upgrades would be good! ;-)
Thanx, Paul
> > +struct rcu_sync_struct {
> > + int gp_state;
> > + int gp_count;
> > + wait_queue_head_t gp_wait;
> > +
> > + int cb_state;
> > + struct rcu_head cb_head;
> > +
> > + void (*sync)(void);
> > + void (*call)(struct rcu_head *, void (*)(struct rcu_head *));
>
> Yes, and we also need rcu_sync_struct->barrier(). From the patch I was
> working on:
>
> void rcu_sync_wait_for_callback(struct rcu_sync *sync)
> {
> int cb_state;
>
> BUG_ON(sync->gp_count);
>
> spin_lock_irq(&sync->state_lock);
> if (sync->cb_state == CB_REPLAY)
> sync->cb_state = CB_PENDING;
> cb_state = sync->cb_state;
> spin_unlock_irq(&sync->state_lock);
>
> if (cb_state != CB_IDLE) {
> rcu_barrier_sched();
> BUG_ON(sync->cb_state != CB_IDLE);
> }
> }
>
> It should be called if you are going to kfree the object.
>
> Perhaps another rcu_sync_struct->state_change(new_state) callback (set
> by the user) makes sense too, this can help (for example) to implement
> the array of semaphores with a single rcu_sync_struct (freeze_super).
>
> Thanks.
>
> Oleg.
>
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