[PATCH -tip V2 00/10] workqueue: break affinity initiatively

[Lai Jiangshan]

From: Lai Jiangshan <laijs@xxxxxxxxxxxxxxxxx>

06249738a41a ("workqueue: Manually break affinity on hotplug")
said that scheduler will not force break affinity for us.

But workqueue highly depends on the old behavior. Many parts of the codes
relies on it, 06249738a41a ("workqueue: Manually break affinity on hotplug")
is not enough to change it, and the commit has flaws in itself too.

It doesn't handle for worker detachment.
It doesn't handle for worker attachement, mainly worker creation
  which is handled by Valentin Schneider's patch [1].
It doesn't handle for unbound workers which might be possible
per-cpu-kthread.

We need to thoroughly update the way workqueue handles affinity
in cpu hot[un]plug, what is this patchset intends to do and
replace the Valentin Schneider's patch [1].  The equivalent patch
is patch 10.

Patch 1 fixes a flaw reported by Hillf Danton <hdanton@xxxxxxxx>.
I have to include this fix because later patches depends on it.

The patchset is based on tip/master rather than workqueue tree,
because the patchset is a complement for 06249738a41a ("workqueue:
Manually break affinity on hotplug") which is only in tip/master by now.

And TJ acked to route the series through tip.

Changed from V1:
	Add TJ's acked-by for the whole patchset

	Add more words to the comments and the changelog, mainly derived
	from discussion with Peter.

	Update the comments as TJ suggested.
	
	Update a line of code as Valentin suggested.

	Add Valentin's ack for patch 10 because "Seems alright to me." and
	add Valentin's comments to the changelog which is integral.

[1]: https://lore.kernel.org/r/ff62e3ee994efb3620177bf7b19fab16f4866845.camel@xxxxxxxxxx
[V1 patcheset]: https://lore.kernel.org/lkml/20201214155457.3430-1-jiangshanlai@xxxxxxxxx/

Cc: Hillf Danton <hdanton@xxxxxxxx>
Cc: Valentin Schneider <valentin.schneider@xxxxxxx>
Cc: Qian Cai <cai@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Vincent Donnefort <vincent.donnefort@xxxxxxx>
Cc: Tejun Heo <tj@xxxxxxxxxx>

Lai Jiangshan (10):
  workqueue: restore unbound_workers' cpumask correctly
  workqueue: use cpu_possible_mask instead of cpu_active_mask to break
    affinity
  workqueue: Manually break affinity on pool detachment
  workqueue: don't set the worker's cpumask when kthread_bind_mask()
  workqueue: introduce wq_online_cpumask
  workqueue: use wq_online_cpumask in restore_unbound_workers_cpumask()
  workqueue: Manually break affinity on hotplug for unbound pool
  workqueue: reorganize workqueue_online_cpu()
  workqueue: reorganize workqueue_offline_cpu() unbind_workers()
  workqueue: Fix affinity of kworkers when attaching into pool

 kernel/workqueue.c | 214 ++++++++++++++++++++++++++++-----------------
 1 file changed, 132 insertions(+), 82 deletions(-)

-- 
2.19.1.6.gb485710b