Messages in this thread | | | Date | Wed, 23 Jul 2014 05:16:15 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH 07/16] rcu: Save and restore irq flags in rcu_gp_cleanup() |
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On Wed, Jul 23, 2014 at 01:09:44AM -0400, Pranith Kumar wrote: > We use raw_spin_lock_irqsave/restore() family of functions throughout the code > but for two locations. This commit replaces raw_spin_lock_irq()/unlock_irq() > with irqsave/restore() in one such location. This is not strictly necessary, > so I did not change the other location. I will update the other location if > this is accepted :) > > This commit changes raw_spin_lock_irq()/unlock_irq() to lock_irqsave()/restore(). > > Signed-off-by: Pranith Kumar <bobby.prani@gmail.com>
I sympathize, as I used to take the approach that you are advocating.
The reason that I changed is that we -know- that interrupts are enabled at this point in the code, so there is no point in incurring the extra cognitive and machine overhead of the _irqsave() variant. Plus the current code has documentation benefits -- it tells you that the author felt that irqs could not possible be disabled here.
So sorry, but no.
Thanx, Paul
> --- > kernel/rcu/tree.c | 14 +++++++------- > 1 file changed, 7 insertions(+), 7 deletions(-) > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > index b14cecd..5dcbf36 100644 > --- a/kernel/rcu/tree.c > +++ b/kernel/rcu/tree.c > @@ -1706,13 +1706,13 @@ static int rcu_gp_fqs(struct rcu_state *rsp, int fqs_state_in) > */ > static void rcu_gp_cleanup(struct rcu_state *rsp) > { > - unsigned long gp_duration; > + unsigned long gp_duration, flags; > bool needgp = false; > int nocb = 0; > struct rcu_data *rdp; > struct rcu_node *rnp = rcu_get_root(rsp); > > - raw_spin_lock_irq(&rnp->lock); > + raw_spin_lock_irqsave(&rnp->lock, flags); > smp_mb__after_unlock_lock(); > gp_duration = jiffies - rsp->gp_start; > if (gp_duration > rsp->gp_max) > @@ -1726,7 +1726,7 @@ static void rcu_gp_cleanup(struct rcu_state *rsp) > * safe for us to drop the lock in order to mark the grace > * period as completed in all of the rcu_node structures. > */ > - raw_spin_unlock_irq(&rnp->lock); > + raw_spin_unlock_irqrestore(&rnp->lock, flags); > > /* > * Propagate new ->completed value to rcu_node structures so > @@ -1738,7 +1738,7 @@ static void rcu_gp_cleanup(struct rcu_state *rsp) > * grace period is recorded in any of the rcu_node structures. > */ > rcu_for_each_node_breadth_first(rsp, rnp) { > - raw_spin_lock_irq(&rnp->lock); > + raw_spin_lock_irqsave(&rnp->lock, flags); > smp_mb__after_unlock_lock(); > ACCESS_ONCE(rnp->completed) = rsp->gpnum; > rdp = this_cpu_ptr(rsp->rda); > @@ -1746,11 +1746,11 @@ static void rcu_gp_cleanup(struct rcu_state *rsp) > needgp = __note_gp_changes(rsp, rnp, rdp) || needgp; > /* smp_mb() provided by prior unlock-lock pair. */ > nocb += rcu_future_gp_cleanup(rsp, rnp); > - raw_spin_unlock_irq(&rnp->lock); > + raw_spin_unlock_irqrestore(&rnp->lock, flags); > cond_resched(); > } > rnp = rcu_get_root(rsp); > - raw_spin_lock_irq(&rnp->lock); > + raw_spin_lock_irqsave(&rnp->lock, flags); > smp_mb__after_unlock_lock(); /* Order GP before ->completed update. */ > rcu_nocb_gp_set(rnp, nocb); > > @@ -1767,7 +1767,7 @@ static void rcu_gp_cleanup(struct rcu_state *rsp) > ACCESS_ONCE(rsp->gpnum), > TPS("newreq")); > } > - raw_spin_unlock_irq(&rnp->lock); > + raw_spin_unlock_irqrestore(&rnp->lock, flags); > } > > /* > -- > 2.0.0.rc2 >
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