| Message ID | 52707B02.7030100@linux.vnet.ibm.com (mailing list archive) |
|---|---|
| State | Not Applicable |
| Headers | show |
Hi Preeti, > nr_busy_cpus parameter is used by nohz_kick_needed() to find out the number > of busy cpus in a sched domain which has SD_SHARE_PKG_RESOURCES flag set. > Therefore instead of updating nr_busy_cpus at every level of sched domain, > since it is irrelevant, we can update this parameter only at the parent > domain of the sd which has this flag set. Introduce a per-cpu parameter > sd_busy which represents this parent domain. > > In nohz_kick_needed() we directly query the nr_busy_cpus parameter > associated with the groups of sd_busy. > > By associating sd_busy with the highest domain which has > SD_SHARE_PKG_RESOURCES flag set, we cover all lower level domains which could > have this flag set and trigger nohz_idle_balancing if any of the levels have > more than one busy cpu. > > sd_busy is irrelevant for asymmetric load balancing. However sd_asym has been > introduced to represent the highest sched domain which has SD_ASYM_PACKING flag set > so that it can be queried directly when required. > > While we are at it, we might as well change the nohz_idle parameter to be > updated at the sd_busy domain level alone and not the base domain level of a CPU. > This will unify the concept of busy cpus at just one level of sched domain > where it is currently used. > > Signed-off-by: Preeti U Murthy<preeti@linux.vnet.ibm.com> > --- > kernel/sched/core.c | 6 ++++++ > kernel/sched/fair.c | 38 ++++++++++++++++++++------------------ > kernel/sched/sched.h | 2 ++ > 3 files changed, 28 insertions(+), 18 deletions(-) > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index c06b8d3..e6a6244 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -5271,6 +5271,8 @@ DEFINE_PER_CPU(struct sched_domain *, sd_llc); > DEFINE_PER_CPU(int, sd_llc_size); > DEFINE_PER_CPU(int, sd_llc_id); > DEFINE_PER_CPU(struct sched_domain *, sd_numa); > +DEFINE_PER_CPU(struct sched_domain *, sd_busy); > +DEFINE_PER_CPU(struct sched_domain *, sd_asym); > > static void update_top_cache_domain(int cpu) > { > @@ -5282,6 +5284,7 @@ static void update_top_cache_domain(int cpu) > if (sd) { > id = cpumask_first(sched_domain_span(sd)); > size = cpumask_weight(sched_domain_span(sd)); > + rcu_assign_pointer(per_cpu(sd_busy, cpu), sd->parent); > } consider a machine with single socket, dual core with HT enabled. The top most domain is also the highest domain with SD_SHARE_PKG_RESOURCES flag set, i.e MC domain (the machine toplogy consist of SIBLING and MC domain). # lstopo-no-graphics --no-bridges --no-io Machine (7869MB) + Socket L#0 + L3 L#0 (3072KB) L2 L#0 (256KB) + L1d L#0 (32KB) + L1i L#0 (32KB) + Core L#0 PU L#0 (P#0) PU L#1 (P#1) L2 L#1 (256KB) + L1d L#1 (32KB) + L1i L#1 (32KB) + Core L#1 PU L#2 (P#2) PU L#3 (P#3) With this approach parent of MC domain is NULL and given that sd_busy is NULL, nr_busy_cpus of sched domain sd_busy will never be incremented/decremented. Resulting is nohz_kick_needed returning 0. Thanks, Kamalesh.
Hi Kamalesh, On 10/30/2013 02:53 PM, Kamalesh Babulal wrote: > Hi Preeti, > >> nr_busy_cpus parameter is used by nohz_kick_needed() to find out the number >> of busy cpus in a sched domain which has SD_SHARE_PKG_RESOURCES flag set. >> Therefore instead of updating nr_busy_cpus at every level of sched domain, >> since it is irrelevant, we can update this parameter only at the parent >> domain of the sd which has this flag set. Introduce a per-cpu parameter >> sd_busy which represents this parent domain. >> >> In nohz_kick_needed() we directly query the nr_busy_cpus parameter >> associated with the groups of sd_busy. >> >> By associating sd_busy with the highest domain which has >> SD_SHARE_PKG_RESOURCES flag set, we cover all lower level domains which could >> have this flag set and trigger nohz_idle_balancing if any of the levels have >> more than one busy cpu. >> >> sd_busy is irrelevant for asymmetric load balancing. However sd_asym has been >> introduced to represent the highest sched domain which has SD_ASYM_PACKING flag set >> so that it can be queried directly when required. >> >> While we are at it, we might as well change the nohz_idle parameter to be >> updated at the sd_busy domain level alone and not the base domain level of a CPU. >> This will unify the concept of busy cpus at just one level of sched domain >> where it is currently used. >> >> Signed-off-by: Preeti U Murthy<preeti@linux.vnet.ibm.com> >> --- >> kernel/sched/core.c | 6 ++++++ >> kernel/sched/fair.c | 38 ++++++++++++++++++++------------------ >> kernel/sched/sched.h | 2 ++ >> 3 files changed, 28 insertions(+), 18 deletions(-) >> >> diff --git a/kernel/sched/core.c b/kernel/sched/core.c >> index c06b8d3..e6a6244 100644 >> --- a/kernel/sched/core.c >> +++ b/kernel/sched/core.c >> @@ -5271,6 +5271,8 @@ DEFINE_PER_CPU(struct sched_domain *, sd_llc); >> DEFINE_PER_CPU(int, sd_llc_size); >> DEFINE_PER_CPU(int, sd_llc_id); >> DEFINE_PER_CPU(struct sched_domain *, sd_numa); >> +DEFINE_PER_CPU(struct sched_domain *, sd_busy); >> +DEFINE_PER_CPU(struct sched_domain *, sd_asym); >> >> static void update_top_cache_domain(int cpu) >> { >> @@ -5282,6 +5284,7 @@ static void update_top_cache_domain(int cpu) >> if (sd) { >> id = cpumask_first(sched_domain_span(sd)); >> size = cpumask_weight(sched_domain_span(sd)); >> + rcu_assign_pointer(per_cpu(sd_busy, cpu), sd->parent); >> } > > > consider a machine with single socket, dual core with HT enabled. The top most > domain is also the highest domain with SD_SHARE_PKG_RESOURCES flag set, > i.e MC domain (the machine toplogy consist of SIBLING and MC domain). > > # lstopo-no-graphics --no-bridges --no-io > Machine (7869MB) + Socket L#0 + L3 L#0 (3072KB) > L2 L#0 (256KB) + L1d L#0 (32KB) + L1i L#0 (32KB) + Core L#0 > PU L#0 (P#0) > PU L#1 (P#1) > L2 L#1 (256KB) + L1d L#1 (32KB) + L1i L#1 (32KB) + Core L#1 > PU L#2 (P#2) > PU L#3 (P#3) > > With this approach parent of MC domain is NULL and given that sd_busy is NULL, > nr_busy_cpus of sched domain sd_busy will never be incremented/decremented. > Resulting is nohz_kick_needed returning 0. Right and it *should* return 0. There is no sibling domain that can offload tasks from it. Therefore there is no point kicking nohz idle balance. Regards Preeti U Murthy > > Thanks, > Kamalesh. >
diff --git a/kernel/sched/core.c b/kernel/sched/core.c index c06b8d3..e6a6244 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -5271,6 +5271,8 @@ DEFINE_PER_CPU(struct sched_domain *, sd_llc); DEFINE_PER_CPU(int, sd_llc_size); DEFINE_PER_CPU(int, sd_llc_id); DEFINE_PER_CPU(struct sched_domain *, sd_numa); +DEFINE_PER_CPU(struct sched_domain *, sd_busy); +DEFINE_PER_CPU(struct sched_domain *, sd_asym); static void update_top_cache_domain(int cpu) { @@ -5282,6 +5284,7 @@ static void update_top_cache_domain(int cpu) if (sd) { id = cpumask_first(sched_domain_span(sd)); size = cpumask_weight(sched_domain_span(sd)); + rcu_assign_pointer(per_cpu(sd_busy, cpu), sd->parent); } rcu_assign_pointer(per_cpu(sd_llc, cpu), sd); @@ -5290,6 +5293,9 @@ static void update_top_cache_domain(int cpu) sd = lowest_flag_domain(cpu, SD_NUMA); rcu_assign_pointer(per_cpu(sd_numa, cpu), sd); + + sd = highest_flag_domain(cpu, SD_ASYM_PACKING); + rcu_assign_pointer(per_cpu(sd_asym, cpu), sd); } /* diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index e9c9549..8602b2c 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -6515,16 +6515,16 @@ static inline void nohz_balance_exit_idle(int cpu) static inline void set_cpu_sd_state_busy(void) { struct sched_domain *sd; + int cpu = smp_processor_id(); rcu_read_lock(); - sd = rcu_dereference_check_sched_domain(this_rq()->sd); + sd = rcu_dereference(per_cpu(sd_busy, cpu)); if (!sd || !sd->nohz_idle) goto unlock; sd->nohz_idle = 0; - for (; sd; sd = sd->parent) - atomic_inc(&sd->groups->sgp->nr_busy_cpus); + atomic_inc(&sd->groups->sgp->nr_busy_cpus); unlock: rcu_read_unlock(); } @@ -6532,16 +6532,16 @@ unlock: void set_cpu_sd_state_idle(void) { struct sched_domain *sd; + int cpu = smp_processor_id(); rcu_read_lock(); - sd = rcu_dereference_check_sched_domain(this_rq()->sd); + sd = rcu_dereference(per_cpu(sd_busy, cpu)); if (!sd || sd->nohz_idle) goto unlock; sd->nohz_idle = 1; - for (; sd; sd = sd->parent) - atomic_dec(&sd->groups->sgp->nr_busy_cpus); + atomic_dec(&sd->groups->sgp->nr_busy_cpus); unlock: rcu_read_unlock(); } @@ -6748,6 +6748,8 @@ static inline int nohz_kick_needed(struct rq *rq, int cpu) { unsigned long now = jiffies; struct sched_domain *sd; + struct sched_group_power *sgp; + int nr_busy; if (unlikely(idle_cpu(cpu))) return 0; @@ -6773,22 +6775,22 @@ static inline int nohz_kick_needed(struct rq *rq, int cpu) goto need_kick; rcu_read_lock(); - for_each_domain(cpu, sd) { - struct sched_group *sg = sd->groups; - struct sched_group_power *sgp = sg->sgp; - int nr_busy = atomic_read(&sgp->nr_busy_cpus); + sd = rcu_dereference(per_cpu(sd_busy, cpu)); - if (sd->flags & SD_SHARE_PKG_RESOURCES && nr_busy > 1) - goto need_kick_unlock; + if (sd) { + sgp = sd->groups->sgp; + nr_busy = atomic_read(&sgp->nr_busy_cpus); - if (sd->flags & SD_ASYM_PACKING - && (cpumask_first_and(nohz.idle_cpus_mask, - sched_domain_span(sd)) < cpu)) + if (nr_busy > 1) goto need_kick_unlock; - - if (!(sd->flags & (SD_SHARE_PKG_RESOURCES | SD_ASYM_PACKING))) - break; } + + sd = rcu_dereference(per_cpu(sd_asym, cpu)); + + if (sd && (cpumask_first_and(nohz.idle_cpus_mask, + sched_domain_span(sd)) < cpu)) + goto need_kick_unlock; + rcu_read_unlock(); return 0; diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index ffc7087..c8cb145 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -623,6 +623,8 @@ DECLARE_PER_CPU(struct sched_domain *, sd_llc); DECLARE_PER_CPU(int, sd_llc_size); DECLARE_PER_CPU(int, sd_llc_id); DECLARE_PER_CPU(struct sched_domain *, sd_numa); +DECLARE_PER_CPU(struct sched_domain *, sd_busy); +DECLARE_PER_CPU(struct sched_domain *, sd_asym); struct sched_group_power { atomic_t ref;