Messages in this thread | | | Subject | Re: [PATCH v5 03/12] sched: fix avg_load computation | From | Tim Chen <> | Date | Thu, 04 Sep 2014 09:26:51 -0700 |
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On Thu, 2014-09-04 at 09:17 +0200, Vincent Guittot wrote: > On 4 September 2014 01:43, Tim Chen <tim.c.chen@linux.intel.com> wrote: > > On Wed, 2014-09-03 at 13:09 +0200, Vincent Guittot wrote: > >> On 30 August 2014 14:00, Preeti U Murthy <preeti@linux.vnet.ibm.com> wrote: > >> > Hi Vincent, > >> > > >> > On 08/26/2014 04:36 PM, Vincent Guittot wrote: > >> >> The computation of avg_load and avg_load_per_task should only takes into > >> >> account the number of cfs tasks. The non cfs task are already taken into > >> >> account by decreasing the cpu's capacity and they will be tracked in the > >> >> CPU's utilization (group_utilization) of the next patches > >> >> > >> >> Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org> > >> >> --- > >> >> kernel/sched/fair.c | 4 ++-- > >> >> 1 file changed, 2 insertions(+), 2 deletions(-) > >> >> > >> >> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > >> >> index 87b9dc7..b85e9f7 100644 > >> >> --- a/kernel/sched/fair.c > >> >> +++ b/kernel/sched/fair.c > >> >> @@ -4092,7 +4092,7 @@ static unsigned long capacity_of(int cpu) > >> >> static unsigned long cpu_avg_load_per_task(int cpu) > >> >> { > >> >> struct rq *rq = cpu_rq(cpu); > >> >> - unsigned long nr_running = ACCESS_ONCE(rq->nr_running); > >> >> + unsigned long nr_running = ACCESS_ONCE(rq->cfs.h_nr_running); > >> >> unsigned long load_avg = rq->cfs.runnable_load_avg; > >> >> > >> >> if (nr_running) > >> >> @@ -5985,7 +5985,7 @@ static inline void update_sg_lb_stats(struct lb_env *env, > >> >> load = source_load(i, load_idx); > >> >> > >> >> sgs->group_load += load; > >> >> - sgs->sum_nr_running += rq->nr_running; > >> >> + sgs->sum_nr_running += rq->cfs.h_nr_running; > >> >> > >> >> if (rq->nr_running > 1) > >> >> *overload = true; > >> >> > >> > > >> > Why do we probe rq->nr_running while we do load balancing? Should not we > >> > be probing cfs_rq->nr_running instead? We are interested after all in > >> > load balancing fair tasks right? The reason I ask this is, I was > >> > wondering if we need to make the above similar change in more places in > >> > load balancing. > >> > >> Hi Preeti, > >> > >> Yes, we should probably the test rq->cfs.h_nr_running > 0 before > >> setting overload. > >> > > > > The overload indicator is used for knowing when we can totally avoid > > load balancing to a cpu that is about to go idle. > > We can avoid load balancing when no cpu has more than 1 task. So if you > > have say just one fair task and multiple deadline tasks on a cpu, > > and another cpu about to go idle, you should turn on normal load > > balancing in the idle path by setting overload to true. > > The newly idle load balancing can only affect CFS tasks so triggering > a load_balance because a cpu is overloaded by rt tasks only, will not > change anything. > > > > > So setting overload should be set based on rq->nr_running and not on > > rq->cfs.h_nr_running. > > We should probably use both values like below > > if ((rq->nr_running > 1) && ( rq->cfs.h_nr_running > 0))
Yes, this modification is the correct one that takes care of the condition I objected to previously.
Thanks.
Tim
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