| Message ID | 1532093554-30504-2-git-send-email-morten.rasmussen@arm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
Hi Morten On 20/07/18 14:32, Morten Rasmussen wrote: > The SD_ASYM_CPUCAPACITY sched_domain flag is supposed to mark the > sched_domain in the hierarchy where all cpu capacities are visible for > any cpu's point of view on asymmetric cpu capacity systems. The > scheduler can then take to take capacity asymmetry into account when Did you mean "s/take to take/try to take/"? > balancing at this level. It also serves as an indicator for how wide > task placement heuristics have to search to consider all available cpu > capacities as asymmetric systems might often appear symmetric at > smallest level(s) of the sched_domain hierarchy. > > The flag has been around for while but so far only been set by > out-of-tree code in Android kernels. One solution is to let each > architecture provide the flag through a custom sched_domain topology > array and associated mask and flag functions. However, > SD_ASYM_CPUCAPACITY is special in the sense that it depends on the > capacity and presence of all cpus in the system, i.e. when hotplugging > all cpus out except those with one particular cpu capacity the flag > should disappear even if the sched_domains don't collapse. Similarly, > the flag is affected by cpusets where load-balancing is turned off. > Detecting when the flags should be set therefore depends not only on > topology information but also the cpuset configuration and hotplug > state. The arch code doesn't have easy access to the cpuset > configuration. > > Instead, this patch implements the flag detection in generic code where > cpusets and hotplug state is already taken care of. All the arch is > responsible for is to implement arch_scale_cpu_capacity() and force a > full rebuild of the sched_domain hierarchy if capacities are updated, > e.g. later in the boot process when cpufreq has initialized. > > cc: Ingo Molnar <mingo@redhat.com> > cc: Peter Zijlstra <peterz@infradead.org> > > Signed-off-by: Morten Rasmussen <morten.rasmussen@arm.com> > --- > include/linux/sched/topology.h | 2 +- > kernel/sched/topology.c | 81 ++++++++++++++++++++++++++++++++++++++---- > 2 files changed, 76 insertions(+), 7 deletions(-) > > diff --git a/include/linux/sched/topology.h b/include/linux/sched/topology.h > index 26347741ba50..4fe2e49ab13b 100644 > --- a/include/linux/sched/topology.h > +++ b/include/linux/sched/topology.h > @@ -23,7 +23,7 @@ > #define SD_BALANCE_FORK 0x0008 /* Balance on fork, clone */ > #define SD_BALANCE_WAKE 0x0010 /* Balance on wakeup */ > #define SD_WAKE_AFFINE 0x0020 /* Wake task to waking CPU */ > -#define SD_ASYM_CPUCAPACITY 0x0040 /* Groups have different max cpu capacities */ > +#define SD_ASYM_CPUCAPACITY 0x0040 /* Domain members have different cpu capacities */ > #define SD_SHARE_CPUCAPACITY 0x0080 /* Domain members share cpu capacity */ > #define SD_SHARE_POWERDOMAIN 0x0100 /* Domain members share power domain */ > #define SD_SHARE_PKG_RESOURCES 0x0200 /* Domain members share cpu pkg resources */ > diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c > index 05a831427bc7..b8f41d557612 100644 > --- a/kernel/sched/topology.c > +++ b/kernel/sched/topology.c > @@ -1061,7 +1061,6 @@ static struct cpumask ***sched_domains_numa_masks; > * SD_SHARE_PKG_RESOURCES - describes shared caches > * SD_NUMA - describes NUMA topologies > * SD_SHARE_POWERDOMAIN - describes shared power domain > - * SD_ASYM_CPUCAPACITY - describes mixed capacity topologies > * > * Odd one out, which beside describing the topology has a quirk also > * prescribes the desired behaviour that goes along with it: > @@ -1073,13 +1072,12 @@ static struct cpumask ***sched_domains_numa_masks; > SD_SHARE_PKG_RESOURCES | \ > SD_NUMA | \ > SD_ASYM_PACKING | \ > - SD_ASYM_CPUCAPACITY | \ > SD_SHARE_POWERDOMAIN) > > static struct sched_domain * > sd_init(struct sched_domain_topology_level *tl, > const struct cpumask *cpu_map, > - struct sched_domain *child, int cpu) > + struct sched_domain *child, int dflags, int cpu) > { > struct sd_data *sdd = &tl->data; > struct sched_domain *sd = *per_cpu_ptr(sdd->sd, cpu); > @@ -1100,6 +1098,9 @@ sd_init(struct sched_domain_topology_level *tl, > "wrong sd_flags in topology description\n")) > sd_flags &= ~TOPOLOGY_SD_FLAGS; > > + /* Apply detected topology flags */ > + sd_flags |= dflags; > + > *sd = (struct sched_domain){ > .min_interval = sd_weight, > .max_interval = 2*sd_weight, > @@ -1607,9 +1608,9 @@ static void __sdt_free(const struct cpumask *cpu_map) > > static struct sched_domain *build_sched_domain(struct sched_domain_topology_level *tl, > const struct cpumask *cpu_map, struct sched_domain_attr *attr, > - struct sched_domain *child, int cpu) > + struct sched_domain *child, int dflags, int cpu) > { > - struct sched_domain *sd = sd_init(tl, cpu_map, child, cpu); > + struct sched_domain *sd = sd_init(tl, cpu_map, child, dflags, cpu); > > if (child) { > sd->level = child->level + 1; > @@ -1636,6 +1637,65 @@ static struct sched_domain *build_sched_domain(struct sched_domain_topology_leve > } > > /* > + * Find the sched_domain_topology_level where all cpu capacities are visible > + * for all cpus. > + */ > +static struct sched_domain_topology_level > +*asym_cpu_capacity_level(const struct cpumask *cpu_map) > +{ > + int i, j, asym_level = 0; > + bool asym = false; > + struct sched_domain_topology_level *tl, *asym_tl = NULL; > + unsigned long cap; > + > + /* Is there any asymmetry? */ > + cap = arch_scale_cpu_capacity(NULL, cpumask_first(cpu_map)); > + > + for_each_cpu(i, cpu_map) { > + if (arch_scale_cpu_capacity(NULL, i) != cap) { > + asym = true; > + break; > + } > + } > + > + if (!asym) > + return NULL; > + > + /* > + * Examine topology from all cpu's point of views to detect the lowest > + * sched_domain_topology_level where a highest capacity cpu is visible > + * to everyone. > + */ > + for_each_cpu(i, cpu_map) { > + unsigned long max_capacity = arch_scale_cpu_capacity(NULL, i); > + int tl_id = 0; > + > + for_each_sd_topology(tl) { > + if (tl_id < asym_level) > + goto next_level; > + I think if you increment and then continue here you might save the extra branch. I didn't look at any disassembly though to verify the generated code. I wonder if we can introduce for_each_sd_topology_from(tl, starting_level) so that you can start searching from a provided level - which will make this skipping logic unnecessary? So the code will look like for_each_sd_topology_from(tl, asymc_level) { ... } > + for_each_cpu_and(j, tl->mask(i), cpu_map) { > + unsigned long capacity; > + > + capacity = arch_scale_cpu_capacity(NULL, j); > + > + if (capacity <= max_capacity) > + continue; > + > + max_capacity = capacity; > + asym_level = tl_id; > + asym_tl = tl; > + } > +next_level: > + tl_id++; > + } > + } > + > + return asym_tl; > +} > + > + > +/* > * Build sched domains for a given set of CPUs and attach the sched domains > * to the individual CPUs > */ > @@ -1647,18 +1707,27 @@ build_sched_domains(const struct cpumask *cpu_map, struct sched_domain_attr *att > struct s_data d; > struct rq *rq = NULL; > int i, ret = -ENOMEM; > + struct sched_domain_topology_level *tl_asym; > > alloc_state = __visit_domain_allocation_hell(&d, cpu_map); > if (alloc_state != sa_rootdomain) > goto error; > > + tl_asym = asym_cpu_capacity_level(cpu_map); > + Or maybe this is not a hot path and we don't care that much about optimizing the search since you call it unconditionally here even for systems that don't care? > /* Set up domains for CPUs specified by the cpu_map: */ > for_each_cpu(i, cpu_map) { > struct sched_domain_topology_level *tl; > > sd = NULL; > for_each_sd_topology(tl) { > - sd = build_sched_domain(tl, cpu_map, attr, sd, i); > + int dflags = 0; > + > + if (tl == tl_asym) > + dflags |= SD_ASYM_CPUCAPACITY; > + > + sd = build_sched_domain(tl, cpu_map, attr, sd, dflags, i); > + > if (tl == sched_domain_topology) > *per_cpu_ptr(d.sd, i) = sd; > if (tl->flags & SDTL_OVERLAP)
On Mon, Jul 23, 2018 at 02:25:34PM +0100, Qais Yousef wrote: > Hi Morten > > On 20/07/18 14:32, Morten Rasmussen wrote: > >The SD_ASYM_CPUCAPACITY sched_domain flag is supposed to mark the > >sched_domain in the hierarchy where all cpu capacities are visible for > >any cpu's point of view on asymmetric cpu capacity systems. The > >scheduler can then take to take capacity asymmetry into account when > > Did you mean "s/take to take/try to take/"? Yes. [...] > >+ /* > >+ * Examine topology from all cpu's point of views to detect the lowest > >+ * sched_domain_topology_level where a highest capacity cpu is visible > >+ * to everyone. > >+ */ > >+ for_each_cpu(i, cpu_map) { > >+ unsigned long max_capacity = arch_scale_cpu_capacity(NULL, i); > >+ int tl_id = 0; > >+ > >+ for_each_sd_topology(tl) { > >+ if (tl_id < asym_level) > >+ goto next_level; > >+ > > I think if you increment and then continue here you might save the extra > branch. I didn't look at any disassembly though to verify the generated > code. > > I wonder if we can introduce for_each_sd_topology_from(tl, starting_level) > so that you can start searching from a provided level - which will make this > skipping logic unnecessary? So the code will look like > > for_each_sd_topology_from(tl, asymc_level) { > ... > } Both options would work. Increment+contrinue instead of goto would be slightly less readable I think since we would still have the increment at the end of the loop, but easy to do. Introducing for_each_sd_topology_from() improve things too, but I wonder if it is worth it. > >@@ -1647,18 +1707,27 @@ build_sched_domains(const struct cpumask *cpu_map, struct sched_domain_attr *att > > struct s_data d; > > struct rq *rq = NULL; > > int i, ret = -ENOMEM; > >+ struct sched_domain_topology_level *tl_asym; > > alloc_state = __visit_domain_allocation_hell(&d, cpu_map); > > if (alloc_state != sa_rootdomain) > > goto error; > >+ tl_asym = asym_cpu_capacity_level(cpu_map); > >+ > > Or maybe this is not a hot path and we don't care that much about optimizing > the search since you call it unconditionally here even for systems that > don't care? It does increase the cost of things like hotplug slightly and repartitioning of root_domains a slightly but I don't see how we can avoid it if we want generic code to set this flag. If the costs are not acceptable I think the only option is to make the detection architecture specific. In any case, AFAIK rebuilding the sched_domain hierarchy shouldn't be a normal and common thing to do. If checking for the flag is not acceptable on SMP-only architectures, I can move it under arch/arm[,64] although it is not as clean. Morten
On 23/07/18 16:27, Morten Rasmussen wrote: [...] >>> + /* >>> + * Examine topology from all cpu's point of views to detect the lowest >>> + * sched_domain_topology_level where a highest capacity cpu is visible >>> + * to everyone. >>> + */ >>> + for_each_cpu(i, cpu_map) { >>> + unsigned long max_capacity = arch_scale_cpu_capacity(NULL, i); >>> + int tl_id = 0; >>> + >>> + for_each_sd_topology(tl) { >>> + if (tl_id < asym_level) >>> + goto next_level; >>> + >> I think if you increment and then continue here you might save the extra >> branch. I didn't look at any disassembly though to verify the generated >> code. >> >> I wonder if we can introduce for_each_sd_topology_from(tl, starting_level) >> so that you can start searching from a provided level - which will make this >> skipping logic unnecessary? So the code will look like >> >> for_each_sd_topology_from(tl, asymc_level) { >> ... >> } > Both options would work. Increment+contrinue instead of goto would be > slightly less readable I think since we would still have the increment > at the end of the loop, but easy to do. Introducing > for_each_sd_topology_from() improve things too, but I wonder if it is > worth it. I don't mind the current form to be honest. I agree it's not worth it if it is called infrequent enough. >>> @@ -1647,18 +1707,27 @@ build_sched_domains(const struct cpumask *cpu_map, struct sched_domain_attr *att >>> struct s_data d; >>> struct rq *rq = NULL; >>> int i, ret = -ENOMEM; >>> + struct sched_domain_topology_level *tl_asym; >>> alloc_state = __visit_domain_allocation_hell(&d, cpu_map); >>> if (alloc_state != sa_rootdomain) >>> goto error; >>> + tl_asym = asym_cpu_capacity_level(cpu_map); >>> + >> Or maybe this is not a hot path and we don't care that much about optimizing >> the search since you call it unconditionally here even for systems that >> don't care? > It does increase the cost of things like hotplug slightly and > repartitioning of root_domains a slightly but I don't see how we can > avoid it if we want generic code to set this flag. If the costs are not > acceptable I think the only option is to make the detection architecture > specific. I think hotplug is already expensive and this overhead would be small in comparison. But this could be called when frequency changes if I understood correctly - this is the one I wasn't sure how 'hot' it could be. I wouldn't expect frequency changes at a very high rate because it's relatively expensive too.. > In any case, AFAIK rebuilding the sched_domain hierarchy shouldn't be a > normal and common thing to do. If checking for the flag is not > acceptable on SMP-only architectures, I can move it under arch/arm[,64] > although it is not as clean. > I like the approach and I think it's nice and clean. If it actually appears in some profiles I think we have room to optimize it.
On Mon, Jul 23, 2018 at 05:07:50PM +0100, Qais Yousef wrote: > On 23/07/18 16:27, Morten Rasmussen wrote: > >It does increase the cost of things like hotplug slightly and > >repartitioning of root_domains a slightly but I don't see how we can > >avoid it if we want generic code to set this flag. If the costs are not > >acceptable I think the only option is to make the detection architecture > >specific. > > I think hotplug is already expensive and this overhead would be small in > comparison. But this could be called when frequency changes if I understood > correctly - this is the one I wasn't sure how 'hot' it could be. I wouldn't > expect frequency changes at a very high rate because it's relatively > expensive too.. A frequency change shouldn't lead to a flag change or a rebuild of the sched_domain hierarhcy. The situations where the hierarchy should be rebuild to update the flag is during boot as we only know the amount of asymmetry once cpufreq has been initialized, when cpus are hotplugged in/out, and when root_domains change due to cpuset reconfiguration. So it should be a relatively rare event.
On 24/07/18 09:37, Morten Rasmussen wrote: > On Mon, Jul 23, 2018 at 05:07:50PM +0100, Qais Yousef wrote: >> On 23/07/18 16:27, Morten Rasmussen wrote: >>> It does increase the cost of things like hotplug slightly and >>> repartitioning of root_domains a slightly but I don't see how we can >>> avoid it if we want generic code to set this flag. If the costs are not >>> acceptable I think the only option is to make the detection architecture >>> specific. >> I think hotplug is already expensive and this overhead would be small in >> comparison. But this could be called when frequency changes if I understood >> correctly - this is the one I wasn't sure how 'hot' it could be. I wouldn't >> expect frequency changes at a very high rate because it's relatively >> expensive too.. > A frequency change shouldn't lead to a flag change or a rebuild of the > sched_domain hierarhcy. The situations where the hierarchy should be > rebuild to update the flag is during boot as we only know the amount of > asymmetry once cpufreq has been initialized, when cpus are hotplugged > in/out, and when root_domains change due to cpuset reconfiguration. So > it should be a relatively rare event. Ah OK I misunderstood that part then. The series LGTM then.
* Morten Rasmussen <morten.rasmussen@arm.com> wrote: > The SD_ASYM_CPUCAPACITY sched_domain flag is supposed to mark the > sched_domain in the hierarchy where all cpu capacities are visible for > any cpu's point of view on asymmetric cpu capacity systems. The > /* > + * Find the sched_domain_topology_level where all cpu capacities are visible > + * for all cpus. > + */ > + /* > + * Examine topology from all cpu's point of views to detect the lowest > + * sched_domain_topology_level where a highest capacity cpu is visible > + * to everyone. > + */ > #define SD_WAKE_AFFINE 0x0020 /* Wake task to waking CPU */ > -#define SD_ASYM_CPUCAPACITY 0x0040 /* Groups have different max cpu capacities */ > +#define SD_ASYM_CPUCAPACITY 0x0040 /* Domain members have different cpu capacities */ For future reference: *please* capitalize 'CPU' and 'CPUs' in future patches like the rest of the scheduler does. You can see it spelled right above the new definition: 'waking CPU' ;-) (I fixed this up in this patch.) Thanks! Ingo
On Mon, Sep 10, 2018 at 10:21:11AM +0200, Ingo Molnar wrote: > > * Morten Rasmussen <morten.rasmussen@arm.com> wrote: > > > The SD_ASYM_CPUCAPACITY sched_domain flag is supposed to mark the > > sched_domain in the hierarchy where all cpu capacities are visible for > > any cpu's point of view on asymmetric cpu capacity systems. The > > > /* > > + * Find the sched_domain_topology_level where all cpu capacities are visible > > + * for all cpus. > > + */ > > > + /* > > + * Examine topology from all cpu's point of views to detect the lowest > > + * sched_domain_topology_level where a highest capacity cpu is visible > > + * to everyone. > > + */ > > > #define SD_WAKE_AFFINE 0x0020 /* Wake task to waking CPU */ > > -#define SD_ASYM_CPUCAPACITY 0x0040 /* Groups have different max cpu capacities */ > > +#define SD_ASYM_CPUCAPACITY 0x0040 /* Domain members have different cpu capacities */ > > For future reference: *please* capitalize 'CPU' and 'CPUs' in future patches like the rest of > the scheduler does. > > You can see it spelled right above the new definition: 'waking CPU' ;-) > > (I fixed this up in this patch.) Noted. Thanks for fixing up the patch. Morten
diff --git a/include/linux/sched/topology.h b/include/linux/sched/topology.h index 26347741ba50..4fe2e49ab13b 100644 --- a/include/linux/sched/topology.h +++ b/include/linux/sched/topology.h @@ -23,7 +23,7 @@ #define SD_BALANCE_FORK 0x0008 /* Balance on fork, clone */ #define SD_BALANCE_WAKE 0x0010 /* Balance on wakeup */ #define SD_WAKE_AFFINE 0x0020 /* Wake task to waking CPU */ -#define SD_ASYM_CPUCAPACITY 0x0040 /* Groups have different max cpu capacities */ +#define SD_ASYM_CPUCAPACITY 0x0040 /* Domain members have different cpu capacities */ #define SD_SHARE_CPUCAPACITY 0x0080 /* Domain members share cpu capacity */ #define SD_SHARE_POWERDOMAIN 0x0100 /* Domain members share power domain */ #define SD_SHARE_PKG_RESOURCES 0x0200 /* Domain members share cpu pkg resources */ diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c index 05a831427bc7..b8f41d557612 100644 --- a/kernel/sched/topology.c +++ b/kernel/sched/topology.c @@ -1061,7 +1061,6 @@ static struct cpumask ***sched_domains_numa_masks; * SD_SHARE_PKG_RESOURCES - describes shared caches * SD_NUMA - describes NUMA topologies * SD_SHARE_POWERDOMAIN - describes shared power domain - * SD_ASYM_CPUCAPACITY - describes mixed capacity topologies * * Odd one out, which beside describing the topology has a quirk also * prescribes the desired behaviour that goes along with it: @@ -1073,13 +1072,12 @@ static struct cpumask ***sched_domains_numa_masks; SD_SHARE_PKG_RESOURCES | \ SD_NUMA | \ SD_ASYM_PACKING | \ - SD_ASYM_CPUCAPACITY | \ SD_SHARE_POWERDOMAIN) static struct sched_domain * sd_init(struct sched_domain_topology_level *tl, const struct cpumask *cpu_map, - struct sched_domain *child, int cpu) + struct sched_domain *child, int dflags, int cpu) { struct sd_data *sdd = &tl->data; struct sched_domain *sd = *per_cpu_ptr(sdd->sd, cpu); @@ -1100,6 +1098,9 @@ sd_init(struct sched_domain_topology_level *tl, "wrong sd_flags in topology description\n")) sd_flags &= ~TOPOLOGY_SD_FLAGS; + /* Apply detected topology flags */ + sd_flags |= dflags; + *sd = (struct sched_domain){ .min_interval = sd_weight, .max_interval = 2*sd_weight, @@ -1607,9 +1608,9 @@ static void __sdt_free(const struct cpumask *cpu_map) static struct sched_domain *build_sched_domain(struct sched_domain_topology_level *tl, const struct cpumask *cpu_map, struct sched_domain_attr *attr, - struct sched_domain *child, int cpu) + struct sched_domain *child, int dflags, int cpu) { - struct sched_domain *sd = sd_init(tl, cpu_map, child, cpu); + struct sched_domain *sd = sd_init(tl, cpu_map, child, dflags, cpu); if (child) { sd->level = child->level + 1; @@ -1636,6 +1637,65 @@ static struct sched_domain *build_sched_domain(struct sched_domain_topology_leve } /* + * Find the sched_domain_topology_level where all cpu capacities are visible + * for all cpus. + */ +static struct sched_domain_topology_level +*asym_cpu_capacity_level(const struct cpumask *cpu_map) +{ + int i, j, asym_level = 0; + bool asym = false; + struct sched_domain_topology_level *tl, *asym_tl = NULL; + unsigned long cap; + + /* Is there any asymmetry? */ + cap = arch_scale_cpu_capacity(NULL, cpumask_first(cpu_map)); + + for_each_cpu(i, cpu_map) { + if (arch_scale_cpu_capacity(NULL, i) != cap) { + asym = true; + break; + } + } + + if (!asym) + return NULL; + + /* + * Examine topology from all cpu's point of views to detect the lowest + * sched_domain_topology_level where a highest capacity cpu is visible + * to everyone. + */ + for_each_cpu(i, cpu_map) { + unsigned long max_capacity = arch_scale_cpu_capacity(NULL, i); + int tl_id = 0; + + for_each_sd_topology(tl) { + if (tl_id < asym_level) + goto next_level; + + for_each_cpu_and(j, tl->mask(i), cpu_map) { + unsigned long capacity; + + capacity = arch_scale_cpu_capacity(NULL, j); + + if (capacity <= max_capacity) + continue; + + max_capacity = capacity; + asym_level = tl_id; + asym_tl = tl; + } +next_level: + tl_id++; + } + } + + return asym_tl; +} + + +/* * Build sched domains for a given set of CPUs and attach the sched domains * to the individual CPUs */ @@ -1647,18 +1707,27 @@ build_sched_domains(const struct cpumask *cpu_map, struct sched_domain_attr *att struct s_data d; struct rq *rq = NULL; int i, ret = -ENOMEM; + struct sched_domain_topology_level *tl_asym; alloc_state = __visit_domain_allocation_hell(&d, cpu_map); if (alloc_state != sa_rootdomain) goto error; + tl_asym = asym_cpu_capacity_level(cpu_map); + /* Set up domains for CPUs specified by the cpu_map: */ for_each_cpu(i, cpu_map) { struct sched_domain_topology_level *tl; sd = NULL; for_each_sd_topology(tl) { - sd = build_sched_domain(tl, cpu_map, attr, sd, i); + int dflags = 0; + + if (tl == tl_asym) + dflags |= SD_ASYM_CPUCAPACITY; + + sd = build_sched_domain(tl, cpu_map, attr, sd, dflags, i); + if (tl == sched_domain_topology) *per_cpu_ptr(d.sd, i) = sd; if (tl->flags & SDTL_OVERLAP)
The SD_ASYM_CPUCAPACITY sched_domain flag is supposed to mark the sched_domain in the hierarchy where all cpu capacities are visible for any cpu's point of view on asymmetric cpu capacity systems. The scheduler can then take to take capacity asymmetry into account when balancing at this level. It also serves as an indicator for how wide task placement heuristics have to search to consider all available cpu capacities as asymmetric systems might often appear symmetric at smallest level(s) of the sched_domain hierarchy. The flag has been around for while but so far only been set by out-of-tree code in Android kernels. One solution is to let each architecture provide the flag through a custom sched_domain topology array and associated mask and flag functions. However, SD_ASYM_CPUCAPACITY is special in the sense that it depends on the capacity and presence of all cpus in the system, i.e. when hotplugging all cpus out except those with one particular cpu capacity the flag should disappear even if the sched_domains don't collapse. Similarly, the flag is affected by cpusets where load-balancing is turned off. Detecting when the flags should be set therefore depends not only on topology information but also the cpuset configuration and hotplug state. The arch code doesn't have easy access to the cpuset configuration. Instead, this patch implements the flag detection in generic code where cpusets and hotplug state is already taken care of. All the arch is responsible for is to implement arch_scale_cpu_capacity() and force a full rebuild of the sched_domain hierarchy if capacities are updated, e.g. later in the boot process when cpufreq has initialized. cc: Ingo Molnar <mingo@redhat.com> cc: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Morten Rasmussen <morten.rasmussen@arm.com> --- include/linux/sched/topology.h | 2 +- kernel/sched/topology.c | 81 ++++++++++++++++++++++++++++++++++++++---- 2 files changed, 76 insertions(+), 7 deletions(-)