Messages in this thread | | | Date | Fri, 2 Nov 2012 20:19:04 +0000 | From | Christoph Lameter <> | Subject | Re: [PATCH v2 6/9] rcu: use __this_cpu_read helper instead of per_cpu_ptr(p, raw_smp_processor_id()) |
| |
On Fri, 2 Nov 2012, Paul E. McKenney wrote:
> On Sat, Nov 03, 2012 at 12:01:47AM +0800, Shan Wei wrote: > > From: Shan Wei <davidshan@tencent.com> > > > > Signed-off-by: Shan Wei <davidshan@tencent.com> > > --- > > kernel/rcutree.c | 2 +- > > 1 files changed, 1 insertions(+), 1 deletions(-) > > > > diff --git a/kernel/rcutree.c b/kernel/rcutree.c > > index 74df86b..441b945 100644 > > --- a/kernel/rcutree.c > > +++ b/kernel/rcutree.c > > @@ -1960,7 +1960,7 @@ static void force_quiescent_state(struct rcu_state *rsp) > > struct rcu_node *rnp_old = NULL; > > > > /* Funnel through hierarchy to reduce memory contention. */ > > - rnp = per_cpu_ptr(rsp->rda, raw_smp_processor_id())->mynode; > > + rnp = __this_cpu_read(rsp->rda->mynode); > > OK, I'll bite... Why this instead of: > > rnp = __this_cpu_read(rsp->rda)->mynode;
Because this_cpu_read fetches a data word from an address. The addres is relocated using a segment prefix (which contains the offset of the current per cpu area).
And the address needed here is the address of the field of mynode within a structure that has a per cpu address.
| |