Messages in this thread | | | Date | Mon, 21 Apr 2014 18:20:35 -0400 | From | Tejun Heo <> | Subject | Re: [PATCH 1/2 V3] workqueue: substitute POOL_FREEZING with __WQ_FREEZING |
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On Mon, Apr 21, 2014 at 07:59:20PM +0800, Lai Jiangshan wrote: > Only workqueues have freezable or freezing attribution/state, not worker pools. > But POOL_FREEZING adds a suspicious state and makes reviewers confused. > > And it causes freeze_workqueues_begin() and thaw_workqueues() much complicated, > they need to travel all the pools besides wqs. > > Since freezable is workqueue instance's attribution, and freezing > is workqueue instance's state, so we introduce __WQ_FREEZING > to wq->flags instead and remove POOL_FREEZING. > > It is different from POOL_FREEZING, POOL_FREEZING is simply set > all over the world(all pools), while __WQ_FREEZING is only set for freezable wq. > freeze_workqueues_begin()/thaw_workqueues() skip to handle non-freezable wqs > and don't touch the non-freezable wqs' flags.
I was about to apply the patch and have updated the patch description.
While freezing takes place globally, its execution is per-workqueue; however, the current implementation makes use of the per-worker_pool POOL_FREEZING flag. While it's not broken, the flag makes the code more confusing and complicates freeze_workqueues_begin() and thaw_workqueues() by requiring them to walk through all pools.
Since freezable is a workqueue's attribute, and freezing is a workqueue's state, let's introduce __WQ_FREEZING to wq->flags instead and remove POOL_FREEZING.
It is different from POOL_FREEZING in that __WQ_FREEZING is only set for freezable workqueues while POOL_FREEZING is set globally over all pools. freeze_workqueues_begin() and thaw_workqueues() now skip non-freezable workqueues.
But looking at the patch, why do we need __WQ_FREEZING at all? We should be able to test workqueue_freezing in pwq_adjust_max_active(), right? The only requirement there would be that pwq_adjust_max_active(0 is invoked at least once after workqueue_freezing is changed, which is already guaranteed.
Thanks.
-- tejun
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