Commit 41e3ccca authored by Breno Leitao's avatar Breno Leitao Committed by Tejun Heo
Browse files

docs: workqueue: document WQ_AFFN_CACHE_SHARD affinity scope 



Update kernel-parameters.txt and workqueue.rst to reflect the new
cache_shard affinity scope and the default change from cache to
cache_shard.

Signed-off-by: default avatarBreno Leitao <leitao@debian.org>
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
parent 24b2e73f

Documentation/admin-guide/kernel-parameters.txt

+2 −1
Original line number Diff line number Diff line
@@ -8519,7 +8519,8 @@ Kernel parameters 
        workqueue.default_affinity_scope=

			Select the default affinity scope to use for unbound

			workqueues. Can be one of "cpu", "smt", "cache",

			"numa" and "system". Default is "cache". For more

			"cache_shard", "numa" and "system". Default is

			"cache_shard". For more

			information, see the Affinity Scopes section in

			Documentation/core-api/workqueue.rst.

Documentation/core-api/workqueue.rst

+10 −4
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@@ -378,9 +378,9 @@ Affinity Scopes 


An unbound workqueue groups CPUs according to its affinity scope to improve

cache locality. For example, if a workqueue is using the default affinity

scope of "cache", it will group CPUs according to last level cache

boundaries. A work item queued on the workqueue will be assigned to a worker

on one of the CPUs which share the last level cache with the issuing CPU.

scope of "cache_shard", it will group CPUs into sub-LLC shards. A work item

queued on the workqueue will be assigned to a worker on one of the CPUs

within the same shard as the issuing CPU.

Once started, the worker may or may not be allowed to move outside the scope

depending on the ``affinity_strict`` setting of the scope.
@@ -402,7 +402,13 @@ Workqueue currently supports the following affinity scopes. 
``cache``

  CPUs are grouped according to cache boundaries. Which specific cache

  boundary is used is determined by the arch code. L3 is used in a lot of

  cases. This is the default affinity scope.

  cases.



``cache_shard``

  CPUs are grouped into sub-LLC shards of at most ``wq_cache_shard_size``

  cores (default 8, tunable via the ``workqueue.cache_shard_size`` boot

  parameter). Shards are always split on core (SMT group) boundaries.

  This is the default affinity scope.



``numa``

  CPUs are grouped according to NUMA boundaries.