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workqueue: doc change for ST behavior on NUMA systems 

NUMA rework of workqueue made the combination of max_active of 1 and
WQ_UNBOUND insufficient to guarantee ST behavior system wide.

alloc_ordered_queue should now be used instead.

Signed-off-by: Alexei Potashnik <alexei@purestorage.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Alexei Potashnik 2017-07-18 11:12:53 -07:00 committed by Tejun Heo
parent bef85bd7db
commit 0e0cafcda8
1 changed files with 7 additions and 3 deletions
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10
Documentation/core-api/workqueue.rst
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@ -243,11 +243,15 @@ throttling the number of active work items, specifying '0' is
recommended.
Some users depend on the strict execution ordering of ST wq. The
combination of ``@max_active`` of 1 and ``WQ_UNBOUND`` is used to
achieve this behavior. Work items on such wq are always queued to the
unbound worker-pools and only one work item can be active at any given
combination of ``@max_active`` of 1 and ``WQ_UNBOUND`` used to
achieve this behavior. Work items on such wq were always queued to the
unbound worker-pools and only one work item could be active at any given
time thus achieving the same ordering property as ST wq.
In the current implementation the above configuration only guarantees
ST behavior within a given NUMA node. Instead alloc_ordered_queue should
be used to achieve system wide ST behavior.
Example Execution Scenarios
===========================