Messages in this thread | | | From | Paulo Alcantara <> | Subject | Re: [PATCH 17/22] cifs: Use alloc_ordered_workqueue() to create ordered workqueues | Date | Fri, 21 Apr 2023 15:38:57 -0300 |
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Tejun Heo <tj@kernel.org> writes:
> 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. > > Signed-off-by: Tejun Heo <tj@kernel.org> > Cc: Steve French <sfrench@samba.org> > Cc: Paulo Alcantara <pc@cjr.nz> > Cc: Ronnie Sahlberg <lsahlber@redhat.com> > Cc: Shyam Prasad N <sprasad@microsoft.com> > Cc: Tom Talpey <tom@talpey.com> > Cc: linux-cifs@vger.kernel.org > Cc: samba-technical@lists.samba.org > --- > fs/cifs/dfs_cache.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-)
Acked-by: Paulo Alcantara (SUSE) <pc@manguebit.com>
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