Messages in this thread | | | Date | Fri, 16 Apr 2010 07:23:48 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH RFC tip/core/rcu 02/16] rcu: make dead code really dead |
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On Thu, Apr 15, 2010 at 04:52:52PM -0700, Josh Triplett wrote: > On Thu, Apr 15, 2010 at 11:13:25AM -0700, Paul E. McKenney wrote: > > From: Lai Jiangshan <laijs@cn.fujitsu.com> > > > > cleanup: make dead code really dead > > > > Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> > > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> > > --- > > kernel/rcutree.c | 4 ++-- > > 1 files changed, 2 insertions(+), 2 deletions(-) > > > > diff --git a/kernel/rcutree.c b/kernel/rcutree.c > > index e54c123..6042fb8 100644 > > --- a/kernel/rcutree.c > > +++ b/kernel/rcutree.c > > @@ -1236,11 +1236,11 @@ static void force_quiescent_state(struct rcu_state *rsp, int relaxed) > > break; /* grace period idle or initializing, ignore. */ > > > > case RCU_SAVE_DYNTICK: > > - > > - raw_spin_unlock(&rnp->lock); /* irqs remain disabled */ > > if (RCU_SIGNAL_INIT != RCU_SAVE_DYNTICK) > > break; /* So gcc recognizes the dead code. */ > > GCC's new __builtin_unreachable would help here, though obviously we > can't count on 4.5 or newer quite yet. A wrapper in compiler.h would > let us use it when available though.
So at some time when we can count on gcc 4.5 or newer, the code would look something like the following?
if (RCU_SIGNAL_INIT == RCU_SAVE_DYNTICK) this_is_unreachable();
I suppose that in the meantime one could supply the code to use in the unreachable case:
if (RCU_SIGNAL_INIT == RCU_SAVE_DYNTICK) this_is_unreachable(break);
But this is beginning to seem a bit strained to me. ;-)
Thanx, Paul
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