On 09/04/2013 01:59 AM, Paul E. McKenney wrote: > On Tue, Sep 03, 2013 at 01:41:03PM +0800, Chen Gang wrote: >> Hello Maintainers: >> >> Is this issue finished ? >> >> If need additional help from me (e.g. some test things, or others, if >> you have no time, can let me try), please let me know, I should try. > > Ah, sorry, here is the patch. >
Thanks. :-) > Thanx, Paul > > ------------------------------------------------------------------------ > > rcu: Micro-optimize rcu_cpu_has_callbacks() > > The for_each_rcu_flavor() loop unconditionally scans all flavors, even > when the first flavor might have some non-lazy callbacks. Once the > loop has seen a non-lazy callback, further passes through the loop > cannot change the state. This is not a huge problem, given that there > can be at most three RCU flavors (RCU-bh, RCU-preempt, and RCU-sched), > but this code is on the path to idle, so speeding it up even a small > amount would have some benefit. > > This commit therefore does two things: > > 1. Rearranges the order of the list of RCU flavors in order to > place the most active flavor first in the list. The most active > RCU flavor is RCU-preempt, or, if there is no RCU-preempt, > RCU-sched. > > 2. Reworks the for_each_rcu_flavor() to exit early when the first > non-lazy callback is seen, or, in the case where the caller > does not care about non-lazy callbacks (RCU_FAST_NO_HZ=n), > when the first callback is seen. > > Reported-by: Chen Gang <gang.c...@asianux.com> > Signed-off-by: Paul E. McKenney <paul...@linux.vnet.ibm.com> > > diff --git a/kernel/rcutree.c b/kernel/rcutree.c > index b1b959d..38596be 100644 > --- a/kernel/rcutree.c > +++ b/kernel/rcutree.c > @@ -2756,10 +2756,13 @@ static int rcu_cpu_has_callbacks(int cpu, bool > *all_lazy) > > for_each_rcu_flavor(rsp) { > rdp = per_cpu_ptr(rsp->rda, cpu); > - if (rdp->qlen != rdp->qlen_lazy) > + if (!rdp->nxtlist) > + continue; > + hc = true; > + if (rdp->qlen != rdp->qlen_lazy || !all_lazy) { > al = false; > - if (rdp->nxtlist) > - hc = true; > + break; > + } > } > if (all_lazy) > *all_lazy = al; > @@ -3326,8 +3329,8 @@ void __init rcu_init(void) > > rcu_bootup_announce(); > rcu_init_geometry(); > - rcu_init_one(&rcu_sched_state, &rcu_sched_data); > rcu_init_one(&rcu_bh_state, &rcu_bh_data); > + rcu_init_one(&rcu_sched_state, &rcu_sched_data); > __rcu_init_preempt(); > open_softirq(RCU_SOFTIRQ, rcu_process_callbacks); > > > > -- Chen Gang -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/