WORKER_ID_LEN = 10 + WQ_NAME_LEN, /* "kworker/R-" + WQ_NAME_LEN */
};
+/* Layout of shards within one LLC pod */
+struct llc_shard_layout {
+ int nr_large_shards; /* number of large shards (cores_per_shard + 1) */
+ int cores_per_shard; /* base number of cores per default shard */
+ int nr_shards; /* total number of shards */
+ /* nr_default shards = (nr_shards - nr_large_shards) */
+};
+
/*
* We don't want to trap softirq for too long. See MAX_SOFTIRQ_TIME and
* MAX_SOFTIRQ_RESTART in kernel/softirq.c. These are macros because
[WQ_AFFN_CPU] = "cpu",
[WQ_AFFN_SMT] = "smt",
[WQ_AFFN_CACHE] = "cache",
+ [WQ_AFFN_CACHE_SHARD] = "cache_shard",
[WQ_AFFN_NUMA] = "numa",
[WQ_AFFN_SYSTEM] = "system",
};
static bool wq_power_efficient = IS_ENABLED(CONFIG_WQ_POWER_EFFICIENT_DEFAULT);
module_param_named(power_efficient, wq_power_efficient, bool, 0444);
+static unsigned int wq_cache_shard_size = 8;
+module_param_named(cache_shard_size, wq_cache_shard_size, uint, 0444);
+
static bool wq_online; /* can kworkers be created yet? */
static bool wq_topo_initialized __read_mostly = false;
return cpu_to_node(cpu0) == cpu_to_node(cpu1);
}
+/* Maps each CPU to its shard index within the LLC pod it belongs to */
+static int cpu_shard_id[NR_CPUS] __initdata;
+
+/**
+ * llc_count_cores - count distinct cores (SMT groups) within an LLC pod
+ * @pod_cpus: the cpumask of CPUs in the LLC pod
+ * @smt_pods: the SMT pod type, used to identify sibling groups
+ *
+ * A core is represented by the lowest-numbered CPU in its SMT group. Returns
+ * the number of distinct cores found in @pod_cpus.
+ */
+static int __init llc_count_cores(const struct cpumask *pod_cpus,
+ struct wq_pod_type *smt_pods)
+{
+ const struct cpumask *sibling_cpus;
+ int nr_cores = 0, c;
+
+ /*
+ * Count distinct cores by only counting the first CPU in each
+ * SMT sibling group.
+ */
+ for_each_cpu(c, pod_cpus) {
+ sibling_cpus = smt_pods->pod_cpus[smt_pods->cpu_pod[c]];
+ if (cpumask_first(sibling_cpus) == c)
+ nr_cores++;
+ }
+
+ return nr_cores;
+}
+
+/*
+ * llc_shard_size - number of cores in a given shard
+ *
+ * Cores are spread as evenly as possible. The first @nr_large_shards shards are
+ * "large shards" with (cores_per_shard + 1) cores; the rest are "default
+ * shards" with cores_per_shard cores.
+ */
+static int __init llc_shard_size(int shard_id, int cores_per_shard, int nr_large_shards)
+{
+ /* The first @nr_large_shards shards are large shards */
+ if (shard_id < nr_large_shards)
+ return cores_per_shard + 1;
+
+ /* The remaining shards are default shards */
+ return cores_per_shard;
+}
+
+/*
+ * llc_calc_shard_layout - compute the shard layout for an LLC pod
+ * @nr_cores: number of distinct cores in the LLC pod
+ *
+ * Chooses the number of shards that keeps average shard size closest to
+ * wq_cache_shard_size. Returns a struct describing the total number of shards,
+ * the base size of each, and how many are large shards.
+ */
+static struct llc_shard_layout __init llc_calc_shard_layout(int nr_cores)
+{
+ struct llc_shard_layout layout;
+
+ /* Ensure at least one shard; pick the count closest to the target size */
+ layout.nr_shards = max(1, DIV_ROUND_CLOSEST(nr_cores, wq_cache_shard_size));
+ layout.cores_per_shard = nr_cores / layout.nr_shards;
+ layout.nr_large_shards = nr_cores % layout.nr_shards;
+
+ return layout;
+}
+
+/*
+ * llc_shard_is_full - check whether a shard has reached its core capacity
+ * @cores_in_shard: number of cores already assigned to this shard
+ * @shard_id: index of the shard being checked
+ * @layout: the shard layout computed by llc_calc_shard_layout()
+ *
+ * Returns true if @cores_in_shard equals the expected size for @shard_id.
+ */
+static bool __init llc_shard_is_full(int cores_in_shard, int shard_id,
+ const struct llc_shard_layout *layout)
+{
+ return cores_in_shard == llc_shard_size(shard_id, layout->cores_per_shard,
+ layout->nr_large_shards);
+}
+
+/**
+ * llc_populate_cpu_shard_id - populate cpu_shard_id[] for each CPU in an LLC pod
+ * @pod_cpus: the cpumask of CPUs in the LLC pod
+ * @smt_pods: the SMT pod type, used to identify sibling groups
+ * @nr_cores: number of distinct cores in @pod_cpus (from llc_count_cores())
+ *
+ * Walks @pod_cpus in order. At each SMT group leader, advances to the next
+ * shard once the current shard is full. Results are written to cpu_shard_id[].
+ */
+static void __init llc_populate_cpu_shard_id(const struct cpumask *pod_cpus,
+ struct wq_pod_type *smt_pods,
+ int nr_cores)
+{
+ struct llc_shard_layout layout = llc_calc_shard_layout(nr_cores);
+ const struct cpumask *sibling_cpus;
+ /* Count the number of cores in the current shard_id */
+ int cores_in_shard = 0;
+ /* This is a cursor for the shards. Go from zero to nr_shards - 1*/
+ int shard_id = 0;
+ int c;
+
+ /* Iterate at every CPU for a given LLC pod, and assign it a shard */
+ for_each_cpu(c, pod_cpus) {
+ sibling_cpus = smt_pods->pod_cpus[smt_pods->cpu_pod[c]];
+ if (cpumask_first(sibling_cpus) == c) {
+ /* This is the CPU leader for the siblings */
+ if (llc_shard_is_full(cores_in_shard, shard_id, &layout)) {
+ shard_id++;
+ cores_in_shard = 0;
+ }
+ cores_in_shard++;
+ cpu_shard_id[c] = shard_id;
+ } else {
+ /*
+ * The siblings' shard MUST be the same as the leader.
+ * never split threads in the same core.
+ */
+ cpu_shard_id[c] = cpu_shard_id[cpumask_first(sibling_cpus)];
+ }
+ }
+
+ WARN_ON_ONCE(shard_id != (layout.nr_shards - 1));
+}
+
+/**
+ * precompute_cache_shard_ids - assign each CPU its shard index within its LLC
+ *
+ * Iterates over all LLC pods. For each pod, counts distinct cores then assigns
+ * shard indices to all CPUs in the pod. Must be called after WQ_AFFN_CACHE and
+ * WQ_AFFN_SMT have been initialized.
+ */
+static void __init precompute_cache_shard_ids(void)
+{
+ struct wq_pod_type *llc_pods = &wq_pod_types[WQ_AFFN_CACHE];
+ struct wq_pod_type *smt_pods = &wq_pod_types[WQ_AFFN_SMT];
+ const struct cpumask *cpus_sharing_llc;
+ int nr_cores;
+ int pod;
+
+ if (!wq_cache_shard_size) {
+ pr_warn("workqueue: cache_shard_size must be > 0, setting to 1\n");
+ wq_cache_shard_size = 1;
+ }
+
+ for (pod = 0; pod < llc_pods->nr_pods; pod++) {
+ cpus_sharing_llc = llc_pods->pod_cpus[pod];
+
+ /* Number of cores in this given LLC */
+ nr_cores = llc_count_cores(cpus_sharing_llc, smt_pods);
+ llc_populate_cpu_shard_id(cpus_sharing_llc, smt_pods, nr_cores);
+ }
+}
+
+/*
+ * cpus_share_cache_shard - test whether two CPUs belong to the same cache shard
+ *
+ * Two CPUs share a cache shard if they are in the same LLC and have the same
+ * shard index. Used as the pod affinity callback for WQ_AFFN_CACHE_SHARD.
+ */
+static bool __init cpus_share_cache_shard(int cpu0, int cpu1)
+{
+ if (!cpus_share_cache(cpu0, cpu1))
+ return false;
+
+ return cpu_shard_id[cpu0] == cpu_shard_id[cpu1];
+}
+
/**
* workqueue_init_topology - initialize CPU pods for unbound workqueues
*
init_pod_type(&wq_pod_types[WQ_AFFN_CPU], cpus_dont_share);
init_pod_type(&wq_pod_types[WQ_AFFN_SMT], cpus_share_smt);
init_pod_type(&wq_pod_types[WQ_AFFN_CACHE], cpus_share_cache);
+ precompute_cache_shard_ids();
+ init_pod_type(&wq_pod_types[WQ_AFFN_CACHE_SHARD], cpus_share_cache_shard);
init_pod_type(&wq_pod_types[WQ_AFFN_NUMA], cpus_share_numa);
wq_topo_initialized = true;
projects / thirdparty / kernel / linux.git / commitdiff
