Messages in this thread Patch in this message | | | Date | Sat, 06 May 2023 09:40:14 +0800 | From | Wang Yugui <> | Subject | Re: [PATCH v2 16/22] btrfs: Use alloc_ordered_workqueue() to create ordered workqueues |
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Hi,
> 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. > > WHAT TO LOOK FOR > ================ > > The conversions are from > > alloc_workqueue(WQ_UNBOUND | flags, 1, args..) > > to > > alloc_ordered_workqueue(flags, args...) > > which don't cause any functional changes. If you know that fully ordered > execution is not ncessary, please let me know. I'll drop the conversion and > instead add a comment noting the fact to reduce confusion while conversion > is in progress. > > If you aren't fully sure, it's completely fine to let the conversion > through. The behavior will stay exactly the same and we can always > reconsider later. > > As there are follow-up workqueue core changes, I'd really appreciate if the > patch can be routed through the workqueue tree w/ your acks. Thanks. > > v2: btrfs_alloc_workqueue() updated too as suggested by Wang. > > 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, > > Wang, yeah, that's a helper that can't tell whether the caller wants an > ordered wq or not, so it needs to be updated too. How does this look? > > Thanks. > > fs/btrfs/async-thread.c | 7 +++++-- > fs/btrfs/disk-io.c | 2 +- > fs/btrfs/scrub.c | 6 ++++-- > 3 files changed, 10 insertions(+), 5 deletions(-) > > --- a/fs/btrfs/async-thread.c > +++ b/fs/btrfs/async-thread.c > @@ -99,8 +99,11 @@ struct btrfs_workqueue *btrfs_alloc_work > ret->thresh = thresh; > } > > - ret->normal_wq = alloc_workqueue("btrfs-%s", flags, ret->current_active, > - name); > + if (ret->current_active == 1) > + ret->normal_wq = alloc_ordered_workqueue("btrfs-%s", flags, name); > + else > + ret->normal_wq = alloc_workqueue("btrfs-%s", flags, > + ret->current_active, name); > if (!ret->normal_wq) { > kfree(ret); > return NULL;
by test, I noticed some warning caused by void workqueue_set_max_active(struct workqueue_struct *wq, int max_active) if (WARN_ON(wq->flags & __WQ_ORDERED_EXPLICIT)) return;
so I tested again with the flowing fix
diff --git a/fs/btrfs/async-thread.c b/fs/btrfs/async-thread.c index 43c8995..e4b68e9 100644 --- a/fs/btrfs/async-thread.c +++ b/fs/btrfs/async-thread.c @@ -99,8 +99,11 @@ struct btrfs_workqueue *btrfs_alloc_workqueue(struct btrfs_fs_info *fs_info, ret->thresh = thresh; } - ret->normal_wq = alloc_workqueue("btrfs-%s", flags, ret->current_active, - name); + if(limit_active == 1) + ret->normal_wq = alloc_ordered_workqueue("btrfs-%s", flags, name); + else + ret->normal_wq = alloc_workqueue("btrfs-%s", flags, + ret->current_active, name); if (!ret->normal_wq) { kfree(ret); return NULL; @@ -139,7 +139,7 @@ static inline void thresh_exec_hook(struct btrfs_workqueue *wq) long pending; int need_change = 0; - if (wq->thresh == NO_THRESHOLD) + if (wq->thresh == NO_THRESHOLD || wq->limit_active == 1) return; atomic_dec(&wq->pending); we need 'limit_active' at 2nd postition, so I used 'limit_active' and 1st postition too.
Best Regards Wang Yugui (wangyugui@e16-tech.com) 2023/05/06
> --- a/fs/btrfs/disk-io.c > +++ b/fs/btrfs/disk-io.c > @@ -2218,7 +2218,7 @@ static int btrfs_init_workqueues(struct > fs_info->qgroup_rescan_workers = > btrfs_alloc_workqueue(fs_info, "qgroup-rescan", flags, 1, 0); > fs_info->discard_ctl.discard_workers = > - alloc_workqueue("btrfs_discard", WQ_UNBOUND | WQ_FREEZABLE, 1); > + alloc_ordered_workqueue("btrfs_discard", WQ_FREEZABLE); > > if (!(fs_info->workers && fs_info->hipri_workers && > fs_info->delalloc_workers && fs_info->flush_workers && > --- a/fs/btrfs/scrub.c > +++ b/fs/btrfs/scrub.c > @@ -4245,8 +4245,10 @@ static noinline_for_stack int scrub_work > if (refcount_inc_not_zero(&fs_info->scrub_workers_refcnt)) > return 0; > > - scrub_workers = alloc_workqueue("btrfs-scrub", flags, > - is_dev_replace ? 1 : max_active); > + if (is_dev_replace) > + scrub_workers = alloc_ordered_workqueue("btrfs-scrub", flags); > + else > + scrub_workers = alloc_workqueue("btrfs-scrub", flags, max_active); > if (!scrub_workers) > goto fail_scrub_workers; >
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