Messages in this thread |  | | Date | Sat, 9 Apr 2022 08:56:12 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH v2] EXP rcu: Move expedited grace period (GP) work to RT kthread_worker |
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On Sat, Apr 09, 2022 at 03:17:40PM +0800, Hillf Danton wrote: > On Fri, 8 Apr 2022 10:53:53 -0700 Kalesh Singh wrote > > Thanks for the discussion everyone. > > > > We didn't fully switch to kthread workers to avoid changing the > > behavior for users that dont need this low latency exp GPs. Another > > (and perhaps more important) reason is because kthread_worker offers > > reduced concurrency than workqueues which Pual reported can pose > > issues on systems with a large number of CPUs. > > A second ... what issues were reported wrt concurrency, given the output > of grep -nr workqueue block mm drivers. > > Feel free to post a URL link to the issues.
The issues can be easily seen by inspecting kthread_queue_work() and the functions that it invokes. In contrast, normal workqueues uses per-CPU mechanisms to avoid contention, as can equally easily be seen by inspecting queue_work_on() and the functions that it invokes.
Please do feel free to take a look.
If taking a look does not convince you, please construct some in-kernel benchmarks to test the scalability of these two mechanisms. Please note that some care will be required to make sure that you are doing a valid apples-to-apples comparison.
Thanx, Paul
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