* [PATCH v7 0/3] Rework CPU capacity asymmetry detection @ 2021-06-03 14:06 Beata Michalska 2021-06-03 14:06 ` [PATCH v7 1/3] sched/core: Introduce SD_ASYM_CPUCAPACITY_FULL sched_domain flag Beata Michalska ` (2 more replies) 0 siblings, 3 replies; 7+ messages in thread From: Beata Michalska @ 2021-06-03 14:06 UTC (permalink / raw) To: linux-kernel Cc: peterz, mingo, juri.lelli, vincent.guittot, valentin.schneider, dietmar.eggemann, corbet, rdunlap, linux-doc As of now, the asym_cpu_capacity_level will try to locate the lowest topology level where the highest available CPU capacity is being visible to all CPUs. This works perfectly fine for most of existing asymmetric designs out there, though for some possible and completely valid setups, combining different cpu microarchitectures within clusters, this might not be the best approach, resulting in pointing at a level, at which some of the domains might not see any asymmetry at all. This could be problematic for misfit migration and/or energy aware placement. And as such, for affected platforms it might result in custom changes to wake-up and CPU selection paths. As mentioned in the previous version, based on the available sources out there, one of the potentially affected (by original approach) platforms might be Exynos 9820/990 with it's 'sliced' LLC(SLC) divided between the two custom (big) cores and the remaining A75/A55 cores, which seems to be reflected in the made available dt entries for those platforms. The following patches rework how the asymmetric detection is being carried out, allowing pinning the asymmetric topology level to the lowest one, where full range of CPU capacities is visible to all CPUs within given sched domain. The asym_cpu_capacity_level will also keep track of those levels where any scope of asymmetry is being observed, to denote corresponding sched domains with the SD_ASYM_CPUCAPACITY flag and to enable misfit migration for those. In order to distinguish the sched domains with partial vs full range of CPU capacity asymmetry, new sched domain flag has been introduced: SD_ASYM_CPUCAPACITY_FULL. The overall idea of changing the asymmetry detection has been suggested by Valentin Schneider <valentin.schneider@arm.com> Verified on (mostly): - QEMU (version 4.2.1) with variants of possible asymmetric topologies - machine: virt - modifying the device-tree 'cpus' node for virt machine: qemu-system-aarch64 -kernel $KERNEL_IMG -drive format=qcow2,file=$IMAGE -append 'root=/dev/vda earlycon console=ttyAMA0 sched_debug sched_verbose loglevel=15 kmemleak=on' -m 2G --nographic -cpu cortex-a57 -machine virt -smp cores=8 -machine dumpdtb=$CUSTOM_DTB.dtb $KERNEL_PATH/scripts/dtc/dtc -I dtb -O dts $CUSTOM_DTB.dts > $CUSTOM_DTB.dtb (modify the dts) $KERNEL_PATH/scripts/dtc/dtc -I dts -O dtb $CUSTOM_DTB.dts > $CUSTOM_DTB.dtb qemu-system-aarch64 -kernel $KERNEL_IMG -drive format=qcow2,file=$IMAGE -append 'root=/dev/vda earlycon console=ttyAMA0 sched_debug sched_verbose loglevel=15 kmemleak=on' -m 2G --nographic -cpu cortex-a57 -machine virt -smp cores=8 -machine dtb=$CUSTOM_DTB.dtb v7: - Dropping memory in case there is no asymmetry - Changing classify function to get cpumask (sd span) and re-arranging the function - Adding warning for detecting asymmetry on SMT level v6: - improving code readability v5: - building CPUs list based on their capacity now triggered upon init and explicit request from arch specific code to rebuild sched domains - detecting asymmetry scope now done directly in sd_init v4: - Based on Peter's idea, reworking asym detection to use per-cpu capacity list to serve as base for determining the asym scope v3: - Additional style/doc fixes v2: - Fixed style issues - Reworked accessing the cached topology data as suggested by Valentin Beata Michalska (3): sched/core: Introduce SD_ASYM_CPUCAPACITY_FULL sched_domain flag sched/topology: Rework CPU capacity asymmetry detection sched/doc: Update the CPU capacity asymmetry bits Documentation/scheduler/sched-capacity.rst | 6 +- Documentation/scheduler/sched-energy.rst | 2 +- include/linux/sched/sd_flags.h | 10 + kernel/sched/topology.c | 206 +++++++++++++-------- 4 files changed, 143 insertions(+), 81 deletions(-) -- 2.17.1 ^ permalink raw reply [flat|nested] 7+ messages in thread
* [PATCH v7 1/3] sched/core: Introduce SD_ASYM_CPUCAPACITY_FULL sched_domain flag 2021-06-03 14:06 [PATCH v7 0/3] Rework CPU capacity asymmetry detection Beata Michalska @ 2021-06-03 14:06 ` Beata Michalska 2021-06-24 7:39 ` [tip: sched/core] " tip-bot2 for Beata Michalska 2021-06-03 14:06 ` [PATCH v7 2/3] sched/topology: Rework CPU capacity asymmetry detection Beata Michalska 2021-06-03 14:06 ` [PATCH v7 3/3] sched/doc: Update the CPU capacity asymmetry bits Beata Michalska 2 siblings, 1 reply; 7+ messages in thread From: Beata Michalska @ 2021-06-03 14:06 UTC (permalink / raw) To: linux-kernel Cc: peterz, mingo, juri.lelli, vincent.guittot, valentin.schneider, dietmar.eggemann, corbet, rdunlap, linux-doc Introducing new, complementary to SD_ASYM_CPUCAPACITY, sched_domain topology flag, to distinguish between shed_domains where any CPU capacity asymmetry is detected (SD_ASYM_CPUCAPACITY) and ones where a full set of CPU capacities is visible to all domain members (SD_ASYM_CPUCAPACITY_FULL). With the distinction between full and partial CPU capacity asymmetry, brought in by the newly introduced flag, the scope of the original SD_ASYM_CPUCAPACITY flag gets shifted, still maintaining the existing behaviour when one is detected on a given sched domain, allowing misfit migrations within sched domains that do not observe full range of CPU capacities but still do have members with different capacity values. It loses though it's meaning when it comes to the lowest CPU asymmetry sched_domain level per-cpu pointer, which is to be now denoted by SD_ASYM_CPUCAPACITY_FULL flag. Signed-off-by: Beata Michalska <beata.michalska@arm.com> Reviewed-by: Valentin Schneider <valentin.schneider@arm.com> Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com> --- include/linux/sched/sd_flags.h | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/include/linux/sched/sd_flags.h b/include/linux/sched/sd_flags.h index 34b21e971d77..57bde66d95f7 100644 --- a/include/linux/sched/sd_flags.h +++ b/include/linux/sched/sd_flags.h @@ -90,6 +90,16 @@ SD_FLAG(SD_WAKE_AFFINE, SDF_SHARED_CHILD) */ SD_FLAG(SD_ASYM_CPUCAPACITY, SDF_SHARED_PARENT | SDF_NEEDS_GROUPS) +/* + * Domain members have different CPU capacities spanning all unique CPU + * capacity values. + * + * SHARED_PARENT: Set from the topmost domain down to the first domain where + * all available CPU capacities are visible + * NEEDS_GROUPS: Per-CPU capacity is asymmetric between groups. + */ +SD_FLAG(SD_ASYM_CPUCAPACITY_FULL, SDF_SHARED_PARENT | SDF_NEEDS_GROUPS) + /* * Domain members share CPU capacity (i.e. SMT) * -- 2.17.1 ^ permalink raw reply related [flat|nested] 7+ messages in thread
* [tip: sched/core] sched/core: Introduce SD_ASYM_CPUCAPACITY_FULL sched_domain flag 2021-06-03 14:06 ` [PATCH v7 1/3] sched/core: Introduce SD_ASYM_CPUCAPACITY_FULL sched_domain flag Beata Michalska @ 2021-06-24 7:39 ` tip-bot2 for Beata Michalska 0 siblings, 0 replies; 7+ messages in thread From: tip-bot2 for Beata Michalska @ 2021-06-24 7:39 UTC (permalink / raw) To: linux-tip-commits Cc: Beata Michalska, Peter Zijlstra (Intel), Valentin Schneider, Dietmar Eggemann, x86, linux-kernel The following commit has been merged into the sched/core branch of tip: Commit-ID: 2309a05d2abe713f7debc951640b010370c8befb Gitweb: https://git.kernel.org/tip/2309a05d2abe713f7debc951640b010370c8befb Author: Beata Michalska <beata.michalska@arm.com> AuthorDate: Thu, 03 Jun 2021 15:06:25 +01:00 Committer: Peter Zijlstra <peterz@infradead.org> CommitterDate: Thu, 24 Jun 2021 09:07:50 +02:00 sched/core: Introduce SD_ASYM_CPUCAPACITY_FULL sched_domain flag Introducing new, complementary to SD_ASYM_CPUCAPACITY, sched_domain topology flag, to distinguish between shed_domains where any CPU capacity asymmetry is detected (SD_ASYM_CPUCAPACITY) and ones where a full set of CPU capacities is visible to all domain members (SD_ASYM_CPUCAPACITY_FULL). With the distinction between full and partial CPU capacity asymmetry, brought in by the newly introduced flag, the scope of the original SD_ASYM_CPUCAPACITY flag gets shifted, still maintaining the existing behaviour when one is detected on a given sched domain, allowing misfit migrations within sched domains that do not observe full range of CPU capacities but still do have members with different capacity values. It loses though it's meaning when it comes to the lowest CPU asymmetry sched_domain level per-cpu pointer, which is to be now denoted by SD_ASYM_CPUCAPACITY_FULL flag. Signed-off-by: Beata Michalska <beata.michalska@arm.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Valentin Schneider <valentin.schneider@arm.com> Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com> Link: https://lore.kernel.org/r/20210603140627.8409-2-beata.michalska@arm.com --- include/linux/sched/sd_flags.h | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/include/linux/sched/sd_flags.h b/include/linux/sched/sd_flags.h index 34b21e9..57bde66 100644 --- a/include/linux/sched/sd_flags.h +++ b/include/linux/sched/sd_flags.h @@ -91,6 +91,16 @@ SD_FLAG(SD_WAKE_AFFINE, SDF_SHARED_CHILD) SD_FLAG(SD_ASYM_CPUCAPACITY, SDF_SHARED_PARENT | SDF_NEEDS_GROUPS) /* + * Domain members have different CPU capacities spanning all unique CPU + * capacity values. + * + * SHARED_PARENT: Set from the topmost domain down to the first domain where + * all available CPU capacities are visible + * NEEDS_GROUPS: Per-CPU capacity is asymmetric between groups. + */ +SD_FLAG(SD_ASYM_CPUCAPACITY_FULL, SDF_SHARED_PARENT | SDF_NEEDS_GROUPS) + +/* * Domain members share CPU capacity (i.e. SMT) * * SHARED_CHILD: Set from the base domain up until spanned CPUs no longer share ^ permalink raw reply related [flat|nested] 7+ messages in thread
* [PATCH v7 2/3] sched/topology: Rework CPU capacity asymmetry detection 2021-06-03 14:06 [PATCH v7 0/3] Rework CPU capacity asymmetry detection Beata Michalska 2021-06-03 14:06 ` [PATCH v7 1/3] sched/core: Introduce SD_ASYM_CPUCAPACITY_FULL sched_domain flag Beata Michalska @ 2021-06-03 14:06 ` Beata Michalska 2021-06-24 7:39 ` [tip: sched/core] " tip-bot2 for Beata Michalska 2021-06-03 14:06 ` [PATCH v7 3/3] sched/doc: Update the CPU capacity asymmetry bits Beata Michalska 2 siblings, 1 reply; 7+ messages in thread From: Beata Michalska @ 2021-06-03 14:06 UTC (permalink / raw) To: linux-kernel Cc: peterz, mingo, juri.lelli, vincent.guittot, valentin.schneider, dietmar.eggemann, corbet, rdunlap, linux-doc Currently the CPU capacity asymmetry detection, performed through asym_cpu_capacity_level, tries to identify the lowest topology level at which the highest CPU capacity is being observed, not necessarily finding the level at which all possible capacity values are visible to all CPUs, which might be bit problematic for some possible/valid asymmetric topologies i.e.: DIE [ ] MC [ ][ ] CPU [0] [1] [2] [3] [4] [5] [6] [7] Capacity |.....| |.....| |.....| |.....| L M B B Where: arch_scale_cpu_capacity(L) = 512 arch_scale_cpu_capacity(M) = 871 arch_scale_cpu_capacity(B) = 1024 In this particular case, the asymmetric topology level will point at MC, as all possible CPU masks for that level do cover the CPU with the highest capacity. It will work just fine for the first cluster, not so much for the second one though (consider the find_energy_efficient_cpu which might end up attempting the energy aware wake-up for a domain that does not see any asymmetry at all) Rework the way the capacity asymmetry levels are being detected, allowing to point to the lowest topology level (for a given CPU), where full set of available CPU capacities is visible to all CPUs within given domain. As a result, the per-cpu sd_asym_cpucapacity might differ across the domains. This will have an impact on EAS wake-up placement in a way that it might see different range of CPUs to be considered, depending on the given current and target CPUs. Additionally, those levels, where any range of asymmetry (not necessarily full) is being detected will get identified as well. The selected asymmetric topology level will be denoted by SD_ASYM_CPUCAPACITY_FULL sched domain flag whereas the 'sub-levels' would receive the already used SD_ASYM_CPUCAPACITY flag. This allows maintaining the current behaviour for asymmetric topologies, with misfit migration operating correctly on lower levels, if applicable, as any asymmetry is enough to trigger the misfit migration. The logic there relies on the SD_ASYM_CPUCAPACITY flag and does not relate to the full asymmetry level denoted by the sd_asym_cpucapacity pointer. Detecting the CPU capacity asymmetry is being based on a set of available CPU capacities for all possible CPUs. This data is being generated upon init and updated once CPU topology changes are being detected (through arch_update_cpu_topology). As such, any changes to identified CPU capacities (like initializing cpufreq) need to be explicitly advertised by corresponding archs to trigger rebuilding the data. Additional -dflags- parameter, used when building sched domains, has been removed as well, as the asymmetry flags are now being set directly in sd_init. Suggested-by: Peter Zijlstra <peterz@infradead.org> Suggested-by: Valentin Schneider <valentin.schneider@arm.com> Signed-off-by: Beata Michalska <beata.michalska@arm.com> Tested-by: Valentin Schneider <valentin.schneider@arm.com> Reviewed-by: Valentin Schneider <valentin.schneider@arm.com> Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com> --- kernel/sched/topology.c | 209 +++++++++++++++++++++++++--------------- 1 file changed, 131 insertions(+), 78 deletions(-) diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c index 55a0a243e871..148059678308 100644 --- a/kernel/sched/topology.c +++ b/kernel/sched/topology.c @@ -675,7 +675,7 @@ static void update_top_cache_domain(int cpu) sd = highest_flag_domain(cpu, SD_ASYM_PACKING); rcu_assign_pointer(per_cpu(sd_asym_packing, cpu), sd); - sd = lowest_flag_domain(cpu, SD_ASYM_CPUCAPACITY); + sd = lowest_flag_domain(cpu, SD_ASYM_CPUCAPACITY_FULL); rcu_assign_pointer(per_cpu(sd_asym_cpucapacity, cpu), sd); } @@ -1266,6 +1266,116 @@ static void init_sched_groups_capacity(int cpu, struct sched_domain *sd) update_group_capacity(sd, cpu); } +/** + * Asymmetric CPU capacity bits + */ +struct asym_cap_data { + struct list_head link; + unsigned long capacity; + unsigned long cpus[]; +}; + +/* + * Set of available CPUs grouped by their corresponding capacities + * Each list entry contains a CPU mask reflecting CPUs that share the same + * capacity. + * The lifespan of data is unlimited. + */ +static LIST_HEAD(asym_cap_list); + +#define cpu_capacity_span(asym_data) to_cpumask((asym_data)->cpus) + +/* + * Verify whether there is any CPU capacity asymmetry in a given sched domain. + * Provides sd_flags reflecting the asymmetry scope. + */ +static inline int +asym_cpu_capacity_classify(const struct cpumask *sd_span, + const struct cpumask *cpu_map) +{ + struct asym_cap_data *entry; + int count = 0, miss = 0; + + /* + * Count how many unique CPU capacities this domain spans across + * (compare sched_domain CPUs mask with ones representing available + * CPUs capacities). Take into account CPUs that might be offline: + * skip those. + */ + list_for_each_entry(entry, &asym_cap_list, link) { + if (cpumask_intersects(sd_span, cpu_capacity_span(entry))) + ++count; + else if (cpumask_intersects(cpu_map, cpu_capacity_span(entry))) + ++miss; + } + + WARN_ON_ONCE(!count && !list_empty(&asym_cap_list)); + + /* No asymmetry detected */ + if (count < 2) + return 0; + /* Some of the available CPU capacity values have not been detected */ + if (miss) + return SD_ASYM_CPUCAPACITY; + + /* Full asymmetry */ + return SD_ASYM_CPUCAPACITY | SD_ASYM_CPUCAPACITY_FULL; + +} + +static inline void asym_cpu_capacity_update_data(int cpu) +{ + unsigned long capacity = arch_scale_cpu_capacity(cpu); + struct asym_cap_data *entry = NULL; + + list_for_each_entry(entry, &asym_cap_list, link) { + if (capacity == entry->capacity) + goto done; + } + + entry = kzalloc(sizeof(*entry) + cpumask_size(), GFP_KERNEL); + if (WARN_ONCE(!entry, "Failed to allocate memory for asymmetry data\n")) + return; + entry->capacity = capacity; + list_add(&entry->link, &asym_cap_list); +done: + __cpumask_set_cpu(cpu, cpu_capacity_span(entry)); +} + +/* + * Build-up/update list of CPUs grouped by their capacities + * An update requires explicit request to rebuild sched domains + * with state indicating CPU topology changes. + */ +static void asym_cpu_capacity_scan(void) +{ + struct asym_cap_data *entry, *next; + int cpu; + + list_for_each_entry(entry, &asym_cap_list, link) + cpumask_clear(cpu_capacity_span(entry)); + + for_each_cpu_and(cpu, cpu_possible_mask, housekeeping_cpumask(HK_FLAG_DOMAIN)) + asym_cpu_capacity_update_data(cpu); + + list_for_each_entry_safe(entry, next, &asym_cap_list, link) { + if (cpumask_empty(cpu_capacity_span(entry))) { + list_del(&entry->link); + kfree(entry); + } + } + + /* + * Only one capacity value has been detected i.e. this system is symmetric. + * No need to keep this data around. + */ + if (list_is_singular(&asym_cap_list)) { + entry = list_first_entry(&asym_cap_list, typeof(*entry), link); + list_del(&entry->link); + kfree(entry); + } +} + /* * Initializers for schedule domains * Non-inlined to reduce accumulated stack pressure in build_sched_domains() @@ -1399,11 +1509,12 @@ int __read_mostly node_reclaim_distance = RECLAIM_DISTANCE; static struct sched_domain * sd_init(struct sched_domain_topology_level *tl, const struct cpumask *cpu_map, - struct sched_domain *child, int dflags, int cpu) + struct sched_domain *child, int cpu) { struct sd_data *sdd = &tl->data; struct sched_domain *sd = *per_cpu_ptr(sdd->sd, cpu); int sd_id, sd_weight, sd_flags = 0; + struct cpumask *sd_span; #ifdef CONFIG_NUMA /* @@ -1420,9 +1531,6 @@ 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, @@ -1454,13 +1562,19 @@ sd_init(struct sched_domain_topology_level *tl, #endif }; - cpumask_and(sched_domain_span(sd), cpu_map, tl->mask(cpu)); - sd_id = cpumask_first(sched_domain_span(sd)); + sd_span = sched_domain_span(sd); + cpumask_and(sd_span, cpu_map, tl->mask(cpu)); + sd_id = cpumask_first(sd_span); + + sd->flags |= asym_cpu_capacity_classify(sd_span, cpu_map); + + WARN_ONCE((sd->flags & (SD_SHARE_CPUCAPACITY | SD_ASYM_CPUCAPACITY)) == + (SD_SHARE_CPUCAPACITY | SD_ASYM_CPUCAPACITY), + "CPU capacity asymmetry not supported on SMT\n"); /* * Convert topological properties into behaviour. */ - /* Don't attempt to spread across CPUs of different capacities. */ if ((sd->flags & SD_ASYM_CPUCAPACITY) && sd->child) sd->child->flags &= ~SD_PREFER_SIBLING; @@ -1926,9 +2040,9 @@ 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 dflags, int cpu) + struct sched_domain *child, int cpu) { - struct sched_domain *sd = sd_init(tl, cpu_map, child, dflags, cpu); + struct sched_domain *sd = sd_init(tl, cpu_map, child, cpu); if (child) { sd->level = child->level + 1; @@ -1990,65 +2104,6 @@ static bool topology_span_sane(struct sched_domain_topology_level *tl, return true; } -/* - * 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(cpumask_first(cpu_map)); - - for_each_cpu(i, cpu_map) { - if (arch_scale_cpu_capacity(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(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(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 @@ -2061,7 +2116,6 @@ 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; bool has_asym = false; if (WARN_ON(cpumask_empty(cpu_map))) @@ -2071,24 +2125,19 @@ build_sched_domains(const struct cpumask *cpu_map, struct sched_domain_attr *att 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; - int dflags = 0; sd = NULL; for_each_sd_topology(tl) { - if (tl == tl_asym) { - dflags |= SD_ASYM_CPUCAPACITY; - has_asym = true; - } if (WARN_ON(!topology_span_sane(tl, cpu_map, i))) goto error; - sd = build_sched_domain(tl, cpu_map, attr, sd, dflags, i); + sd = build_sched_domain(tl, cpu_map, attr, sd, i); + + has_asym |= sd->flags & SD_ASYM_CPUCAPACITY; if (tl == sched_domain_topology) *per_cpu_ptr(d.sd, i) = sd; @@ -2217,6 +2266,7 @@ int sched_init_domains(const struct cpumask *cpu_map) zalloc_cpumask_var(&fallback_doms, GFP_KERNEL); arch_update_cpu_topology(); + asym_cpu_capacity_scan(); ndoms_cur = 1; doms_cur = alloc_sched_domains(ndoms_cur); if (!doms_cur) @@ -2299,6 +2349,9 @@ void partition_sched_domains_locked(int ndoms_new, cpumask_var_t doms_new[], /* Let the architecture update CPU core mappings: */ new_topology = arch_update_cpu_topology(); + /* Trigger rebuilding CPU capacity asymmetry data */ + if (new_topology) + asym_cpu_capacity_scan(); if (!doms_new) { WARN_ON_ONCE(dattr_new); -- 2.17.1 ^ permalink raw reply related [flat|nested] 7+ messages in thread
* [tip: sched/core] sched/topology: Rework CPU capacity asymmetry detection 2021-06-03 14:06 ` [PATCH v7 2/3] sched/topology: Rework CPU capacity asymmetry detection Beata Michalska @ 2021-06-24 7:39 ` tip-bot2 for Beata Michalska 0 siblings, 0 replies; 7+ messages in thread From: tip-bot2 for Beata Michalska @ 2021-06-24 7:39 UTC (permalink / raw) To: linux-tip-commits Cc: Peter Zijlstra, Valentin Schneider, Beata Michalska, Dietmar Eggemann, x86, linux-kernel The following commit has been merged into the sched/core branch of tip: Commit-ID: c744dc4ab58d1c09624ca3397cf15b142a0e0cb7 Gitweb: https://git.kernel.org/tip/c744dc4ab58d1c09624ca3397cf15b142a0e0cb7 Author: Beata Michalska <beata.michalska@arm.com> AuthorDate: Thu, 03 Jun 2021 15:06:26 +01:00 Committer: Peter Zijlstra <peterz@infradead.org> CommitterDate: Thu, 24 Jun 2021 09:07:51 +02:00 sched/topology: Rework CPU capacity asymmetry detection Currently the CPU capacity asymmetry detection, performed through asym_cpu_capacity_level, tries to identify the lowest topology level at which the highest CPU capacity is being observed, not necessarily finding the level at which all possible capacity values are visible to all CPUs, which might be bit problematic for some possible/valid asymmetric topologies i.e.: DIE [ ] MC [ ][ ] CPU [0] [1] [2] [3] [4] [5] [6] [7] Capacity |.....| |.....| |.....| |.....| L M B B Where: arch_scale_cpu_capacity(L) = 512 arch_scale_cpu_capacity(M) = 871 arch_scale_cpu_capacity(B) = 1024 In this particular case, the asymmetric topology level will point at MC, as all possible CPU masks for that level do cover the CPU with the highest capacity. It will work just fine for the first cluster, not so much for the second one though (consider the find_energy_efficient_cpu which might end up attempting the energy aware wake-up for a domain that does not see any asymmetry at all) Rework the way the capacity asymmetry levels are being detected, allowing to point to the lowest topology level (for a given CPU), where full set of available CPU capacities is visible to all CPUs within given domain. As a result, the per-cpu sd_asym_cpucapacity might differ across the domains. This will have an impact on EAS wake-up placement in a way that it might see different range of CPUs to be considered, depending on the given current and target CPUs. Additionally, those levels, where any range of asymmetry (not necessarily full) is being detected will get identified as well. The selected asymmetric topology level will be denoted by SD_ASYM_CPUCAPACITY_FULL sched domain flag whereas the 'sub-levels' would receive the already used SD_ASYM_CPUCAPACITY flag. This allows maintaining the current behaviour for asymmetric topologies, with misfit migration operating correctly on lower levels, if applicable, as any asymmetry is enough to trigger the misfit migration. The logic there relies on the SD_ASYM_CPUCAPACITY flag and does not relate to the full asymmetry level denoted by the sd_asym_cpucapacity pointer. Detecting the CPU capacity asymmetry is being based on a set of available CPU capacities for all possible CPUs. This data is being generated upon init and updated once CPU topology changes are being detected (through arch_update_cpu_topology). As such, any changes to identified CPU capacities (like initializing cpufreq) need to be explicitly advertised by corresponding archs to trigger rebuilding the data. Additional -dflags- parameter, used when building sched domains, has been removed as well, as the asymmetry flags are now being set directly in sd_init. Suggested-by: Peter Zijlstra <peterz@infradead.org> Suggested-by: Valentin Schneider <valentin.schneider@arm.com> Signed-off-by: Beata Michalska <beata.michalska@arm.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Valentin Schneider <valentin.schneider@arm.com> Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com> Tested-by: Valentin Schneider <valentin.schneider@arm.com> Link: https://lore.kernel.org/r/20210603140627.8409-3-beata.michalska@arm.com --- kernel/sched/topology.c | 209 ++++++++++++++++++++++++--------------- 1 file changed, 131 insertions(+), 78 deletions(-) diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c index 053115b..b77ad49 100644 --- a/kernel/sched/topology.c +++ b/kernel/sched/topology.c @@ -675,7 +675,7 @@ static void update_top_cache_domain(int cpu) sd = highest_flag_domain(cpu, SD_ASYM_PACKING); rcu_assign_pointer(per_cpu(sd_asym_packing, cpu), sd); - sd = lowest_flag_domain(cpu, SD_ASYM_CPUCAPACITY); + sd = lowest_flag_domain(cpu, SD_ASYM_CPUCAPACITY_FULL); rcu_assign_pointer(per_cpu(sd_asym_cpucapacity, cpu), sd); } @@ -1267,6 +1267,116 @@ next: } /* + * Asymmetric CPU capacity bits + */ +struct asym_cap_data { + struct list_head link; + unsigned long capacity; + unsigned long cpus[]; +}; + +/* + * Set of available CPUs grouped by their corresponding capacities + * Each list entry contains a CPU mask reflecting CPUs that share the same + * capacity. + * The lifespan of data is unlimited. + */ +static LIST_HEAD(asym_cap_list); + +#define cpu_capacity_span(asym_data) to_cpumask((asym_data)->cpus) + +/* + * Verify whether there is any CPU capacity asymmetry in a given sched domain. + * Provides sd_flags reflecting the asymmetry scope. + */ +static inline int +asym_cpu_capacity_classify(const struct cpumask *sd_span, + const struct cpumask *cpu_map) +{ + struct asym_cap_data *entry; + int count = 0, miss = 0; + + /* + * Count how many unique CPU capacities this domain spans across + * (compare sched_domain CPUs mask with ones representing available + * CPUs capacities). Take into account CPUs that might be offline: + * skip those. + */ + list_for_each_entry(entry, &asym_cap_list, link) { + if (cpumask_intersects(sd_span, cpu_capacity_span(entry))) + ++count; + else if (cpumask_intersects(cpu_map, cpu_capacity_span(entry))) + ++miss; + } + + WARN_ON_ONCE(!count && !list_empty(&asym_cap_list)); + + /* No asymmetry detected */ + if (count < 2) + return 0; + /* Some of the available CPU capacity values have not been detected */ + if (miss) + return SD_ASYM_CPUCAPACITY; + + /* Full asymmetry */ + return SD_ASYM_CPUCAPACITY | SD_ASYM_CPUCAPACITY_FULL; + +} + +static inline void asym_cpu_capacity_update_data(int cpu) +{ + unsigned long capacity = arch_scale_cpu_capacity(cpu); + struct asym_cap_data *entry = NULL; + + list_for_each_entry(entry, &asym_cap_list, link) { + if (capacity == entry->capacity) + goto done; + } + + entry = kzalloc(sizeof(*entry) + cpumask_size(), GFP_KERNEL); + if (WARN_ONCE(!entry, "Failed to allocate memory for asymmetry data\n")) + return; + entry->capacity = capacity; + list_add(&entry->link, &asym_cap_list); +done: + __cpumask_set_cpu(cpu, cpu_capacity_span(entry)); +} + +/* + * Build-up/update list of CPUs grouped by their capacities + * An update requires explicit request to rebuild sched domains + * with state indicating CPU topology changes. + */ +static void asym_cpu_capacity_scan(void) +{ + struct asym_cap_data *entry, *next; + int cpu; + + list_for_each_entry(entry, &asym_cap_list, link) + cpumask_clear(cpu_capacity_span(entry)); + + for_each_cpu_and(cpu, cpu_possible_mask, housekeeping_cpumask(HK_FLAG_DOMAIN)) + asym_cpu_capacity_update_data(cpu); + + list_for_each_entry_safe(entry, next, &asym_cap_list, link) { + if (cpumask_empty(cpu_capacity_span(entry))) { + list_del(&entry->link); + kfree(entry); + } + } + + /* + * Only one capacity value has been detected i.e. this system is symmetric. + * No need to keep this data around. + */ + if (list_is_singular(&asym_cap_list)) { + entry = list_first_entry(&asym_cap_list, typeof(*entry), link); + list_del(&entry->link); + kfree(entry); + } +} + +/* * Initializers for schedule domains * Non-inlined to reduce accumulated stack pressure in build_sched_domains() */ @@ -1399,11 +1509,12 @@ int __read_mostly node_reclaim_distance = RECLAIM_DISTANCE; static struct sched_domain * sd_init(struct sched_domain_topology_level *tl, const struct cpumask *cpu_map, - struct sched_domain *child, int dflags, int cpu) + struct sched_domain *child, int cpu) { struct sd_data *sdd = &tl->data; struct sched_domain *sd = *per_cpu_ptr(sdd->sd, cpu); int sd_id, sd_weight, sd_flags = 0; + struct cpumask *sd_span; #ifdef CONFIG_NUMA /* @@ -1420,9 +1531,6 @@ 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, @@ -1454,13 +1562,19 @@ sd_init(struct sched_domain_topology_level *tl, #endif }; - cpumask_and(sched_domain_span(sd), cpu_map, tl->mask(cpu)); - sd_id = cpumask_first(sched_domain_span(sd)); + sd_span = sched_domain_span(sd); + cpumask_and(sd_span, cpu_map, tl->mask(cpu)); + sd_id = cpumask_first(sd_span); + + sd->flags |= asym_cpu_capacity_classify(sd_span, cpu_map); + + WARN_ONCE((sd->flags & (SD_SHARE_CPUCAPACITY | SD_ASYM_CPUCAPACITY)) == + (SD_SHARE_CPUCAPACITY | SD_ASYM_CPUCAPACITY), + "CPU capacity asymmetry not supported on SMT\n"); /* * Convert topological properties into behaviour. */ - /* Don't attempt to spread across CPUs of different capacities. */ if ((sd->flags & SD_ASYM_CPUCAPACITY) && sd->child) sd->child->flags &= ~SD_PREFER_SIBLING; @@ -1926,9 +2040,9 @@ 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 dflags, int cpu) + struct sched_domain *child, int cpu) { - struct sched_domain *sd = sd_init(tl, cpu_map, child, dflags, cpu); + struct sched_domain *sd = sd_init(tl, cpu_map, child, cpu); if (child) { sd->level = child->level + 1; @@ -1991,65 +2105,6 @@ static bool topology_span_sane(struct sched_domain_topology_level *tl, } /* - * 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(cpumask_first(cpu_map)); - - for_each_cpu(i, cpu_map) { - if (arch_scale_cpu_capacity(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(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(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 */ @@ -2061,7 +2116,6 @@ 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; bool has_asym = false; if (WARN_ON(cpumask_empty(cpu_map))) @@ -2071,24 +2125,19 @@ build_sched_domains(const struct cpumask *cpu_map, struct sched_domain_attr *att 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; - int dflags = 0; sd = NULL; for_each_sd_topology(tl) { - if (tl == tl_asym) { - dflags |= SD_ASYM_CPUCAPACITY; - has_asym = true; - } if (WARN_ON(!topology_span_sane(tl, cpu_map, i))) goto error; - sd = build_sched_domain(tl, cpu_map, attr, sd, dflags, i); + sd = build_sched_domain(tl, cpu_map, attr, sd, i); + + has_asym |= sd->flags & SD_ASYM_CPUCAPACITY; if (tl == sched_domain_topology) *per_cpu_ptr(d.sd, i) = sd; @@ -2217,6 +2266,7 @@ int sched_init_domains(const struct cpumask *cpu_map) zalloc_cpumask_var(&fallback_doms, GFP_KERNEL); arch_update_cpu_topology(); + asym_cpu_capacity_scan(); ndoms_cur = 1; doms_cur = alloc_sched_domains(ndoms_cur); if (!doms_cur) @@ -2299,6 +2349,9 @@ void partition_sched_domains_locked(int ndoms_new, cpumask_var_t doms_new[], /* Let the architecture update CPU core mappings: */ new_topology = arch_update_cpu_topology(); + /* Trigger rebuilding CPU capacity asymmetry data */ + if (new_topology) + asym_cpu_capacity_scan(); if (!doms_new) { WARN_ON_ONCE(dattr_new); ^ permalink raw reply related [flat|nested] 7+ messages in thread
* [PATCH v7 3/3] sched/doc: Update the CPU capacity asymmetry bits 2021-06-03 14:06 [PATCH v7 0/3] Rework CPU capacity asymmetry detection Beata Michalska 2021-06-03 14:06 ` [PATCH v7 1/3] sched/core: Introduce SD_ASYM_CPUCAPACITY_FULL sched_domain flag Beata Michalska 2021-06-03 14:06 ` [PATCH v7 2/3] sched/topology: Rework CPU capacity asymmetry detection Beata Michalska @ 2021-06-03 14:06 ` Beata Michalska 2021-06-24 7:39 ` [tip: sched/core] " tip-bot2 for Beata Michalska 2 siblings, 1 reply; 7+ messages in thread From: Beata Michalska @ 2021-06-03 14:06 UTC (permalink / raw) To: linux-kernel Cc: peterz, mingo, juri.lelli, vincent.guittot, valentin.schneider, dietmar.eggemann, corbet, rdunlap, linux-doc Update the documentation bits referring to capacity aware scheduling with regards to newly introduced SD_ASYM_CPUCAPACITY_FULL sched_domain flag. Signed-off-by: Beata Michalska <beata.michalska@arm.com> Reviewed-by: Valentin Schneider <valentin.schneider@arm.com> Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com> --- Documentation/scheduler/sched-capacity.rst | 6 ++++-- Documentation/scheduler/sched-energy.rst | 2 +- 2 files changed, 5 insertions(+), 3 deletions(-) diff --git a/Documentation/scheduler/sched-capacity.rst b/Documentation/scheduler/sched-capacity.rst index 9b7cbe43b2d1..805f85f330b5 100644 --- a/Documentation/scheduler/sched-capacity.rst +++ b/Documentation/scheduler/sched-capacity.rst @@ -284,8 +284,10 @@ whether the system exhibits asymmetric CPU capacities. Should that be the case: - The sched_asym_cpucapacity static key will be enabled. -- The SD_ASYM_CPUCAPACITY flag will be set at the lowest sched_domain level that - spans all unique CPU capacity values. +- The SD_ASYM_CPUCAPACITY_FULL flag will be set at the lowest sched_domain + level that spans all unique CPU capacity values. +- The SD_ASYM_CPUCAPACITY flag will be set for any sched_domain that spans + CPUs with any range of asymmetry. The sched_asym_cpucapacity static key is intended to guard sections of code that cater to asymmetric CPU capacity systems. Do note however that said key is diff --git a/Documentation/scheduler/sched-energy.rst b/Documentation/scheduler/sched-energy.rst index afe02d394402..8fbce5e767d9 100644 --- a/Documentation/scheduler/sched-energy.rst +++ b/Documentation/scheduler/sched-energy.rst @@ -328,7 +328,7 @@ section lists these dependencies and provides hints as to how they can be met. As mentioned in the introduction, EAS is only supported on platforms with asymmetric CPU topologies for now. This requirement is checked at run-time by -looking for the presence of the SD_ASYM_CPUCAPACITY flag when the scheduling +looking for the presence of the SD_ASYM_CPUCAPACITY_FULL flag when the scheduling domains are built. See Documentation/scheduler/sched-capacity.rst for requirements to be met for this -- 2.17.1 ^ permalink raw reply related [flat|nested] 7+ messages in thread
* [tip: sched/core] sched/doc: Update the CPU capacity asymmetry bits 2021-06-03 14:06 ` [PATCH v7 3/3] sched/doc: Update the CPU capacity asymmetry bits Beata Michalska @ 2021-06-24 7:39 ` tip-bot2 for Beata Michalska 0 siblings, 0 replies; 7+ messages in thread From: tip-bot2 for Beata Michalska @ 2021-06-24 7:39 UTC (permalink / raw) To: linux-tip-commits Cc: Beata Michalska, Peter Zijlstra (Intel), Valentin Schneider, Dietmar Eggemann, x86, linux-kernel The following commit has been merged into the sched/core branch of tip: Commit-ID: adf3c31e18b765ea24eba7b0c1efc076b8ee3d55 Gitweb: https://git.kernel.org/tip/adf3c31e18b765ea24eba7b0c1efc076b8ee3d55 Author: Beata Michalska <beata.michalska@arm.com> AuthorDate: Thu, 03 Jun 2021 15:06:27 +01:00 Committer: Peter Zijlstra <peterz@infradead.org> CommitterDate: Thu, 24 Jun 2021 09:07:51 +02:00 sched/doc: Update the CPU capacity asymmetry bits Update the documentation bits referring to capacity aware scheduling with regards to newly introduced SD_ASYM_CPUCAPACITY_FULL sched_domain flag. Signed-off-by: Beata Michalska <beata.michalska@arm.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Valentin Schneider <valentin.schneider@arm.com> Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com> Link: https://lore.kernel.org/r/20210603140627.8409-4-beata.michalska@arm.com --- Documentation/scheduler/sched-capacity.rst | 6 ++++-- Documentation/scheduler/sched-energy.rst | 2 +- 2 files changed, 5 insertions(+), 3 deletions(-) diff --git a/Documentation/scheduler/sched-capacity.rst b/Documentation/scheduler/sched-capacity.rst index 9b7cbe4..805f85f 100644 --- a/Documentation/scheduler/sched-capacity.rst +++ b/Documentation/scheduler/sched-capacity.rst @@ -284,8 +284,10 @@ whether the system exhibits asymmetric CPU capacities. Should that be the case: - The sched_asym_cpucapacity static key will be enabled. -- The SD_ASYM_CPUCAPACITY flag will be set at the lowest sched_domain level that - spans all unique CPU capacity values. +- The SD_ASYM_CPUCAPACITY_FULL flag will be set at the lowest sched_domain + level that spans all unique CPU capacity values. +- The SD_ASYM_CPUCAPACITY flag will be set for any sched_domain that spans + CPUs with any range of asymmetry. The sched_asym_cpucapacity static key is intended to guard sections of code that cater to asymmetric CPU capacity systems. Do note however that said key is diff --git a/Documentation/scheduler/sched-energy.rst b/Documentation/scheduler/sched-energy.rst index afe02d3..8fbce5e 100644 --- a/Documentation/scheduler/sched-energy.rst +++ b/Documentation/scheduler/sched-energy.rst @@ -328,7 +328,7 @@ section lists these dependencies and provides hints as to how they can be met. As mentioned in the introduction, EAS is only supported on platforms with asymmetric CPU topologies for now. This requirement is checked at run-time by -looking for the presence of the SD_ASYM_CPUCAPACITY flag when the scheduling +looking for the presence of the SD_ASYM_CPUCAPACITY_FULL flag when the scheduling domains are built. See Documentation/scheduler/sched-capacity.rst for requirements to be met for this ^ permalink raw reply related [flat|nested] 7+ messages in thread
end of thread, other threads:[~2021-06-24 7:39 UTC | newest] Thread overview: 7+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2021-06-03 14:06 [PATCH v7 0/3] Rework CPU capacity asymmetry detection Beata Michalska 2021-06-03 14:06 ` [PATCH v7 1/3] sched/core: Introduce SD_ASYM_CPUCAPACITY_FULL sched_domain flag Beata Michalska 2021-06-24 7:39 ` [tip: sched/core] " tip-bot2 for Beata Michalska 2021-06-03 14:06 ` [PATCH v7 2/3] sched/topology: Rework CPU capacity asymmetry detection Beata Michalska 2021-06-24 7:39 ` [tip: sched/core] " tip-bot2 for Beata Michalska 2021-06-03 14:06 ` [PATCH v7 3/3] sched/doc: Update the CPU capacity asymmetry bits Beata Michalska 2021-06-24 7:39 ` [tip: sched/core] " tip-bot2 for Beata Michalska
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