Commit 4cdc8a73 authored by Breno Leitao's avatar Breno Leitao Committed by Tejun Heo
Browse files

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: default avatarBreno Leitao <leitao@debian.org>
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
parent 5920d046

kernel/workqueue.c

+1 −1
Original line number Diff line number Diff line
@@ -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;