Messages in this thread | | | Date | Fri, 26 May 2023 14:52:03 +0200 | From | David Sterba <> | Subject | Re: [PATCH 08/13] btrfs: Use alloc_ordered_workqueue() to create ordered workqueues |
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On Thu, May 25, 2023 at 01:33:08PM -1000, Tejun Heo wrote: > BACKGROUND > ========== > > When multiple work items are queued to a workqueue, their execution order > doesn't match the queueing order. They may get executed in any order and > simultaneously. When fully serialized execution - one by one in the queueing > order - is needed, an ordered workqueue should be used which can be created > with alloc_ordered_workqueue(). > > However, alloc_ordered_workqueue() was a later addition. Before it, an > ordered workqueue could be obtained by creating an UNBOUND workqueue with > @max_active==1. This originally was an implementation side-effect which was > broken by 4c16bd327c74 ("workqueue: restore WQ_UNBOUND/max_active==1 to be > ordered"). Because there were users that depended on the ordered execution, > 5c0338c68706 ("workqueue: restore WQ_UNBOUND/max_active==1 to be ordered") > made workqueue allocation path to implicitly promote UNBOUND workqueues w/ > @max_active==1 to ordered workqueues. > > While this has worked okay, overloading the UNBOUND allocation interface > this way creates other issues. It's difficult to tell whether a given > workqueue actually needs to be ordered and users that legitimately want a > min concurrency level wq unexpectedly gets an ordered one instead. With > planned UNBOUND workqueue updates to improve execution locality and more > prevalence of chiplet designs which can benefit from such improvements, this > isn't a state we wanna be in forever. > > This patch series audits all callsites that create an UNBOUND workqueue w/ > @max_active==1 and converts them to alloc_ordered_workqueue() as necessary. > > BTRFS > ===== > > * fs_info->scrub_workers initialized in scrub_workers_get() was setting > @max_active to 1 when @is_dev_replace is set and it seems that the > workqueue actually needs to be ordered if @is_dev_replace. Update the code > so that alloc_ordered_workqueue() is used if @is_dev_replace. > > * fs_info->discard_ctl.discard_workers initialized in > btrfs_init_workqueues() was directly using alloc_workqueue() w/ > @max_active==1. Converted to alloc_ordered_workqueue(). > > * fs_info->fixup_workers and fs_info->qgroup_rescan_workers initialized in > btrfs_queue_work() use the btrfs's workqueue wrapper, btrfs_workqueue, > which are allocated with btrfs_alloc_workqueue(). > > btrfs_workqueue implements automatic @max_active adjustment which is > disabled when the specified max limix is below a certain threshold, so > calling btrfs_alloc_workqueue() with @limit_active==1 yields an ordered > workqueue whose @max_active won't be changed as the auto-tuning is > disabled. > > This is rather brittle in that nothing clearly indicates that the two > workqueues should be ordered or btrfs_alloc_workqueue() must disable > auto-tuning when @limit_active==1. > > This patch factors out the common btrfs_workqueue init code into > btrfs_init_workqueue() and add explicit btrfs_alloc_ordered_workqueue(). > The two workqueues are converted to use the new ordered allocation > interface. > > Signed-off-by: Tejun Heo <tj@kernel.org> > Cc: Wang Yugui <wangyugui@e16-tech.com> > Cc: Chris Mason <clm@fb.com> > Cc: Josef Bacik <josef@toxicpanda.com> > Cc: David Sterba <dsterba@suse.com> > Cc: linux-btrfs@vger.kernel.org > --- > Hello, > > David, I think this is a bit too invasive to carry through workqueue tree. > If this looks okay, can you plase apply route it through the btrfs tree?
Yesd and I actually prefer to take such patches via btrfs tree unless there's a strong dependency on other patches from another subsystem. Thanks.
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