From 63c5484e74952f60f5810256bd69814d167b8d22 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Mon, 7 Aug 2023 15:57:24 -1000 Subject: workqueue: Add multiple affinity scopes and interface to select them Add three more affinity scopes - WQ_AFFN_CPU, SMT and CACHE - and make CACHE the default. The code changes to actually add the additional scopes are trivial. Also add module parameter "workqueue.default_affinity_scope" to override the default scope and "affinity_scope" sysfs file to configure it per workqueue. wq_dump.py and documentations are updated accordingly. This enables significant flexibility in configuring how unbound workqueues behave. If affinity scope is set to "cpu", it'll behave close to a per-cpu workqueue. On the other hand, "system" removes all locality boundaries. Many modern machines have multiple L3 caches often while being mostly uniform in terms of memory access. Thus, workqueue's previous behavior of spreading work items in each NUMA node had negative performance implications from unncessarily crossing L3 boundaries between issue and execution. However, picking a finer grained affinity scope also has a downside in that an issuer in one group can't utilize CPUs in other groups. While dependent on the specifics of workload, there's usually a noticeable penalty in crossing L3 boundaries, so let's default to CACHE. This issue will be further addressed and documented with examples in future patches. Signed-off-by: Tejun Heo --- Documentation/admin-guide/kernel-parameters.txt | 12 ++++++++++++ 1 file changed, 12 insertions(+) (limited to 'Documentation/admin-guide/kernel-parameters.txt') diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 2b89cbc39713..732c5c7e3fa5 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -7007,6 +7007,18 @@ The default value of this parameter is determined by the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT. + 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 + information, see the Affinity Scopes section in + Documentation/core-api/workqueue.rst. + + This can be updated after boot through the matching + file under /sys/module/workqueue/parameters. + However, the changed default will only apply to + unbound workqueues created afterwards. + workqueue.debug_force_rr_cpu Workqueue used to implicitly guarantee that work items queued without explicit CPU specified are put -- cgit v1.2.3