Messages in this thread | | | Date | Wed, 27 Apr 2022 19:56:50 -0400 | Subject | Re: [PATCH] locking/rwsem: Allow slowpath writer to ignore handoff bit if not set by first waiter | From | Waiman Long <> |
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On 4/27/22 19:16, John Donnelly wrote: > On 4/27/22 12:31 PM, Waiman Long wrote: >> With commit d257cc8cb8d5 ("locking/rwsem: Make handoff bit handling more >> consistent"), the writer that sets the handoff bit can be interrupted >> out without clearing the bit if the wait queue isn't empty. This >> disables >> reader and writer optimistic lock spinning and stealing. >> >> Now if a non-first writer in the queue is somehow woken up or first >> entering the waiting loop, it can't acquire the lock. This is not >> the case before that commit as the writer that set the handoff bit >> will clear it when exiting out via the out_nolock path. This is less >> efficient as the busy rwsem stays in an unlock state for a longer time. >> >> This patch allows a non-first writer to ignore the handoff bit if it >> is not originally set or initiated by the first waiter. >> >> Fixes: d257cc8cb8d5 ("locking/rwsem: Make handoff bit handling more >> consistent") > > Hi Waiman, > > 1. You likely need : > > Cc: <stable@vger.kernel.org> > > Since d257cc8cb8d5 has been migrated to other LTS threads (5.15.y for > sure) .
Since the commit has a fixes tag, the stable will automatically pick it up.
> > 2. I had posted this earlier: > > [PATCH 5.15 1/1] Revert "locking/rwsem: Make handoff bit handling more > consistent" > > That is likely not needed now. Right. The patch was created to fix a problem reported by another user. So reverting it may not the right move. > > > 3. Please add : > > Reported-by: Jorge Lopez <jorge.jo.lopez@oracle.com> > > We can likely test this, but I can't give a ETA when that will happen. > > >> Signed-off-by: Waiman Long <longman@redhat.com> > > Acked-by: John Donnelly <john.p.donnelly@oracle.com>
Will add the that when I send out the next version.
Cheers, Longman
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