Messages in this thread | | | Date | Wed, 25 Sep 2013 10:55:30 +0800 | From | Chen Gang <> | Subject | Re: [PATCH tip/core/rcu 08/11] rcu: Micro-optimize rcu_cpu_has_callbacks() |
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Thank you for your whole work, firstly :-).
And your suggestion about testing (in our discussion) is also valuable to me.
I need start LTP in q4. After referenced your suggestion, my first step for using/learning LTP is not mainly for finding kernel issues, but for testing kernel (to improve my kernel testing efficiency).
When I want to find issues by reading code, I will consider about LTP too (I will try to find issues which can be tested by LTP).
On 09/25/2013 09:29 AM, Paul E. McKenney wrote: > From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> > > 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.chen@asianux.com> > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> > --- > kernel/rcutree.c | 11 +++++++---- > 1 file changed, 7 insertions(+), 4 deletions(-) > > diff --git a/kernel/rcutree.c b/kernel/rcutree.c > index e6f2e8f..49464ad 100644 > --- a/kernel/rcutree.c > +++ b/kernel/rcutree.c > @@ -2727,10 +2727,13 @@ 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; > @@ -3297,8 +3300,8 @@ 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
-- Chen Gang
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