Messages in this thread Patch in this message | | | Subject | Re: sched: Improve load balancing in the presence of idle CPUs | From | Tim Chen <> | Date | Tue, 07 Apr 2015 12:39:24 -0700 |
| |
On Tue, 2015-04-07 at 10:42 -0700, Jason Low wrote: > On Fri, 2015-04-03 at 15:35 -0700, Tim Chen wrote: > > I think we can get rid of the done_balancing boolean > > and make it a bit easier to read if we change the above code to > > > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > > index bcfe320..08317dc 100644 > > --- a/kernel/sched/fair.c > > +++ b/kernel/sched/fair.c > > @@ -7557,8 +7557,13 @@ static void nohz_idle_balance(struct rq *this_rq, enum cpu_idle_type idle) > > * work being done for other cpus. Next load > > * balancing owner will pick it up. > > */ > > - if (need_resched()) > > - break; > > + if (need_resched()) { > > + /* preparing to bail, kicking other cpu to continue */ > > + clear_bit(NOHZ_BALANCE_KICK, nohz_flags(this_cpu)); > > + if (nohz_kick_needed(this_rq)) > > + nohz_balance_kick(); > > + return; > > + } > > Hi Tim, > > We would also need the nohz_kick_needed/nohz_balance_kick if we > initially find that the current CPU is not idle (at the beginning of > nohz_idle_balance). In the above case, we would need to add the code to > 2 locations. > > Would it be better to still keep the done_balancing to avoid having > duplicate code? >
How about consolidating the code for passing the nohz balancing and call it at both places. Something like below. Make the code more readable.
Tim
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 40667cb..16f6904 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -7531,6 +7531,15 @@ out: } #ifdef CONFIG_NO_HZ_COMMON +static inline int nohz_kick_needed(struct rq *rq); + +static void inline pass_nohz_balance(struct rq *this_rq, int this_cpu) +{ + clear_bit(NOHZ_BALANCE_KICK, nohz_flags(this_cpu)); + if (nohz_kick_needed(this_rq)) + nohz_balancer_kick(); +} + /* * In CONFIG_NO_HZ_COMMON case, the idle balance kickee will do the * rebalancing for all the cpus for whom scheduler ticks are stopped. @@ -7542,8 +7551,10 @@ static void nohz_idle_balance(struct rq *this_rq, enum cpu_idle_type idle) int balance_cpu; if (idle != CPU_IDLE || - !test_bit(NOHZ_BALANCE_KICK, nohz_flags(this_cpu))) - goto end; + !test_bit(NOHZ_BALANCE_KICK, nohz_flags(this_cpu))) { + pass_nohz_balance(this_rq, this_cpu); + return; + } for_each_cpu(balance_cpu, nohz.idle_cpus_mask) { if (balance_cpu == this_cpu || !idle_cpu(balance_cpu)) @@ -7554,8 +7565,10 @@ static void nohz_idle_balance(struct rq *this_rq, enum cpu_idle_type idle) * work being done for other cpus. Next load * balancing owner will pick it up. */ - if (need_resched()) - break; + if (need_resched()) { + pass_nohz_balance(this_rq, this_cpu); + return; + } rq = cpu_rq(balance_cpu); @@ -7575,7 +7588,6 @@ static void nohz_idle_balance(struct rq *this_rq, enum cpu_idle_type idle) this_rq->next_balance = rq->next_balance; } nohz.next_balance = this_rq->next_balance; -end: clear_bit(NOHZ_BALANCE_KICK, nohz_flags(this_cpu)); }
| |