On 8 February 2013 19:05, Vincent Guittot <vincent.guit...@linaro.org> wrote: > On my smp platform which is made of 5 cores in 2 clusters, I have the > nr_busy_cpu field of sched_group_power struct that is not null when the > platform is fully idle. The root cause seems to be: > During the boot sequence, some CPUs reach the idle loop and set their > NOHZ_IDLE flag while waiting for others CPUs to boot. But the nr_busy_cpus > field is initialized later with the assumption that all CPUs are in the busy > state whereas some CPUs have already set their NOHZ_IDLE flag. > We set the NOHZ_IDLE flag when nr_busy_cpus is initialized to 0 in order to > have a coherent configuration. > > The patch 2/2 protects this init against an update of NOHZ_IDLE flag because > a NULL sched_domain is attached to the CPU during the build of the new > sched_domain so nohz_kick_needed and set_cpu_sd_state_busy are not called and > can't clear the NOHZ_IDLE flag
Hi Frederic, With this v3, the initialization of NOHZ_IDLE and nr_busy_cpus is be protected against any race condition because the initial state is the idle state so if a cpu enters idle, it keeps the same state and we can't set a busy state until the initialization is complete thanks to the NULL domain. Regards, Vincent > > Signed-off-by: Vincent Guittot <vincent.guit...@linaro.org> > --- > kernel/sched/core.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 26058d0..c730a4e 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -5884,7 +5884,9 @@ static void init_sched_groups_power(int cpu, struct > sched_domain *sd) > return; > > update_group_power(sd, cpu); > - atomic_set(&sg->sgp->nr_busy_cpus, sg->group_weight); > + atomic_set(&sg->sgp->nr_busy_cpus, 0); > + set_bit(NOHZ_IDLE, nohz_flags(cpu)); > + > } > > int __weak arch_sd_sibling_asym_packing(void) > -- > 1.7.9.5 > _______________________________________________ linaro-dev mailing list linaro-dev@lists.linaro.org http://lists.linaro.org/mailman/listinfo/linaro-dev
