From: Breno Leitao Date: Wed, 1 Apr 2026 13:03:54 +0000 (-0700) Subject: workqueue: set WQ_AFFN_CACHE_SHARD as the default affinity scope X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=4cdc8a7389d5025051f6c4a60fb5b7cb9b7960bb;p=thirdparty%2Fkernel%2Flinux.git workqueue: set WQ_AFFN_CACHE_SHARD as the default affinity scope Set WQ_AFFN_CACHE_SHARD as the default affinity scope for unbound workqueues. On systems where many CPUs share one LLC, the previous default (WQ_AFFN_CACHE) collapses all CPUs to a single worker pool, causing heavy spinlock contention on pool->lock. WQ_AFFN_CACHE_SHARD subdivides each LLC into smaller groups, providing a better balance between locality and contention. Users can revert to the previous behavior with workqueue.default_affinity_scope=cache. On systems with 8 or fewer cores per LLC, CACHE_SHARD produces a single shard covering the entire LLC, making it functionally identical to the previous CACHE default. The sharding only activates when an LLC has more than 8 cores. Signed-off-by: Breno Leitao Signed-off-by: Tejun Heo --- diff --git a/kernel/workqueue.c b/kernel/workqueue.c index f4a23e1418a77..b1a28c51d4f23 100644 --- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -450,7 +450,7 @@ static bool wq_topo_initialized __read_mostly = false; static struct kmem_cache *pwq_cache; static struct wq_pod_type wq_pod_types[WQ_AFFN_NR_TYPES]; -static enum wq_affn_scope wq_affn_dfl = WQ_AFFN_CACHE; +static enum wq_affn_scope wq_affn_dfl = WQ_AFFN_CACHE_SHARD; /* buf for wq_update_unbound_pod_attrs(), protected by CPU hotplug exclusion */ static struct workqueue_attrs *unbound_wq_update_pwq_attrs_buf;