From: Chen Yu Date: Wed, 13 May 2026 20:39:15 +0000 (-0700) Subject: sched/cache: Calculate the LLC size and store it in sched_domain X-Git-Url: http://git.ipfire.org/gitweb/index.cgi?a=commitdiff_plain;h=7030513a08776b2ca70fccd5dfddf7bb5c5c88ba;p=thirdparty%2Flinux.git sched/cache: Calculate the LLC size and store it in sched_domain Cache aware scheduling needs to know the LLC size that a process can use, so as to avoid memory-intensive tasks from being over-aggregated on a single LLC. Introduce a preparation patch to add get_effective_llc_bytes() to get the LLC size that a CPU can use. The function can be further enhanced by subtracting the LLC cache ways reserved by resctrl (CAT in Intel RDT, etc). Suggested-by: Peter Zijlstra (Intel) Signed-off-by: Chen Yu Co-developed-by: Tim Chen Signed-off-by: Tim Chen Signed-off-by: Peter Zijlstra (Intel) Tested-by: Tingyin Duan Link: https://patch.msgid.link/37afee09ff608034da0ce149e72d33b6f4698edf.1778703694.git.tim.c.chen@linux.intel.com --- diff --git a/drivers/base/cacheinfo.c b/drivers/base/cacheinfo.c index 391ac5e3d2f56..70701d3bc81c6 100644 --- a/drivers/base/cacheinfo.c +++ b/drivers/base/cacheinfo.c @@ -17,6 +17,7 @@ #include #include #include +#include #include #include #include @@ -68,6 +69,24 @@ bool last_level_cache_is_valid(unsigned int cpu) } +/* + * Get the cacheinfo of the LLC associated with @cpu. + * Derived from update_per_cpu_data_slice_size_cpu(). + */ +struct cacheinfo *get_cpu_cacheinfo_llc(unsigned int cpu) +{ + struct cacheinfo *llc; + + if (!last_level_cache_is_valid(cpu)) + return NULL; + + llc = per_cpu_cacheinfo_idx(cpu, cache_leaves(cpu) - 1); + if (llc->type != CACHE_TYPE_DATA && llc->type != CACHE_TYPE_UNIFIED) + return NULL; + + return llc; +} + bool last_level_cache_is_shared(unsigned int cpu_x, unsigned int cpu_y) { struct cacheinfo *llc_x, *llc_y; @@ -1018,6 +1037,7 @@ static int cacheinfo_cpu_online(unsigned int cpu) goto err; if (cpu_map_shared_cache(true, cpu, &cpu_map)) update_per_cpu_data_slice_size(true, cpu, cpu_map); + sched_update_llc_bytes(cpu); return 0; err: free_cache_attributes(cpu); @@ -1036,6 +1056,9 @@ static int cacheinfo_cpu_pre_down(unsigned int cpu) free_cache_attributes(cpu); if (nr_shared > 1) update_per_cpu_data_slice_size(false, cpu, cpu_map); + + sched_update_llc_bytes(cpu); + return 0; } diff --git a/include/linux/cacheinfo.h b/include/linux/cacheinfo.h index c8f4f0a0b874e..fc879ac4cc4f2 100644 --- a/include/linux/cacheinfo.h +++ b/include/linux/cacheinfo.h @@ -89,6 +89,7 @@ int populate_cache_leaves(unsigned int cpu); int cache_setup_acpi(unsigned int cpu); bool last_level_cache_is_valid(unsigned int cpu); bool last_level_cache_is_shared(unsigned int cpu_x, unsigned int cpu_y); +struct cacheinfo *get_cpu_cacheinfo_llc(unsigned int cpu); int fetch_cache_info(unsigned int cpu); int detect_cache_attributes(unsigned int cpu); #ifndef CONFIG_ACPI_PPTT diff --git a/include/linux/sched/topology.h b/include/linux/sched/topology.h index 0036d6b4bd674..fe09d3268bc9c 100644 --- a/include/linux/sched/topology.h +++ b/include/linux/sched/topology.h @@ -106,6 +106,7 @@ struct sched_domain { #ifdef CONFIG_SCHED_CACHE unsigned int llc_max; unsigned int *llc_counts __counted_by_ptr(llc_max); + unsigned long llc_bytes; #endif #ifdef CONFIG_SCHEDSTATS @@ -265,4 +266,10 @@ static inline int task_node(const struct task_struct *p) return cpu_to_node(task_cpu(p)); } +#ifdef CONFIG_SCHED_CACHE +extern void sched_update_llc_bytes(unsigned int cpu); +#else +static inline void sched_update_llc_bytes(unsigned int cpu) { } +#endif + #endif /* _LINUX_SCHED_TOPOLOGY_H */ diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c index 9fc99346ef4f9..7248a7279abeb 100644 --- a/kernel/sched/topology.c +++ b/kernel/sched/topology.c @@ -776,9 +776,11 @@ cpu_attach_domain(struct sched_domain *sd, struct root_domain *rd, int cpu) /* move buffer to parent as child is being destroyed */ sd->llc_counts = tmp->llc_counts; sd->llc_max = tmp->llc_max; + sd->llc_bytes = tmp->llc_bytes; /* make sure destroy_sched_domain() does not free it */ tmp->llc_counts = NULL; tmp->llc_max = 0; + tmp->llc_bytes = 0; #endif /* * sched groups hold the flags of the child sched @@ -831,10 +833,42 @@ DEFINE_STATIC_KEY_FALSE(sched_cache_active); /* user wants cache aware scheduling [0 or 1] */ int sysctl_sched_cache_user = 1; +/* + * Get the effective LLC size in bytes that @cpu's bottom sched_domain + * can use. A CPU within a cpuset partition can only use a proportion + * of the physical LLC, scaled by the ratio of the partition's span + * weight to the hardware LLC sharing weight. @sd should be the + * topmost domain with SD_SHARE_LLC. + * + * Returns 0 if cacheinfo is not yet populated. This happens during + * early boot when build_sched_domains() runs before the generic + * cacheinfo framework has been initialized (cacheinfo_cpu_online() + * is a device_initcall cpuhp callback). In that case, + * cacheinfo_cpu_online() will later call sched_update_llc_bytes() + * to fill in the bottom domain's llc_bytes once the cache attributes + * are available. + */ +static unsigned long get_effective_llc_bytes(int cpu, + struct sched_domain *sd) +{ + struct cacheinfo *ci; + unsigned int hw_weight; + + ci = get_cpu_cacheinfo_llc(cpu); + if (!ci) + return 0; + + hw_weight = cpumask_weight(&ci->shared_cpu_map); + if (!hw_weight) + return 0; + + return div_u64((u64)ci->size * sd->span_weight, hw_weight); +} + static bool alloc_sd_llc(const struct cpumask *cpu_map, struct s_data *d) { - struct sched_domain *sd; + struct sched_domain *sd, *top_llc, *parent; unsigned int *p; int i; @@ -848,8 +882,24 @@ static bool alloc_sd_llc(const struct cpumask *cpu_map, if (!p) goto err; - sd->llc_max = max_lid + 1; - sd->llc_counts = p; + top_llc = sd; + /* + * Find the topmost SD_SHARE_LLC domain. + * Not yet attached to the CPU, so per_cpu(sd_llc, i) + * can not be used. + */ + while ((parent = rcu_dereference_protected(top_llc->parent, true)) && + (parent->flags & SD_SHARE_LLC)) + top_llc = parent; + + if (top_llc->flags & SD_SHARE_LLC) { + sd->llc_max = max_lid + 1; + sd->llc_counts = p; + sd->llc_bytes = get_effective_llc_bytes(i, top_llc); + } else { + /* avoid memory leak */ + kfree(p); + } } return true; @@ -860,6 +910,7 @@ err: kfree(sd->llc_counts); sd->llc_counts = NULL; sd->llc_max = 0; + sd->llc_bytes = 0; } } @@ -919,6 +970,47 @@ void sched_cache_active_set_unlocked(void) { return sched_cache_active_set(false); } + +/* + * Update the bottom sched_domain's llc_bytes for @cpu and all its + * LLC siblings. Called from cacheinfo_cpu_online() or + * cacheinfo_cpu_pre_down() with cpu hotplug lock held. + * + * Note: get_effective_llc_bytes() returns 0 on PowerPC. + * thus cache aware scheduling is disabled on PowerPC for + * now. PowerPC does not use the generic cacheinfo framework -- + * it has its own cacheinfo with a separate struct cache hierarchy + * and does not populates the per-CPU struct cpu_cacheinfo array + * that get_cpu_cacheinfo_llc() reads. + */ +void sched_update_llc_bytes(unsigned int cpu) +{ + struct sched_domain *sd, *sdp; + unsigned int i; + + sched_domains_mutex_lock(); + + sdp = rcu_dereference_sched_domain(per_cpu(sd_llc, cpu)); + if (!sdp) + goto unlock; + + /* + * ci->shared_cpu_map is built incrementally as CPUs come + * online, so the first CPU in an LLC initially sees + * hw_weight == 1 and computes an inflated llc_bytes in + * get_effective_llc_bytes(). Re-evaluating every LLC + * sibling on each online event corrects this once the full + * shared_cpu_map is known. + */ + for_each_cpu(i, sched_domain_span(sdp)) { + sd = rcu_dereference_sched_domain(cpu_rq(i)->sd); + if (sd) + sd->llc_bytes = get_effective_llc_bytes(i, sdp); + } + +unlock: + sched_domains_mutex_unlock(); +} #else static bool alloc_sd_llc(const struct cpumask *cpu_map, struct s_data *d)