Messages in this thread | | | Date | Mon, 30 Sep 2013 11:58:29 -0400 | From | Waiman Long <> | Subject | Re: [PATCH] rwsem: reduce spinlock contention in wakeup code path |
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On 09/28/2013 03:33 PM, Linus Torvalds wrote: > On Sat, Sep 28, 2013 at 12:21 PM, Ingo Molnar<mingo@kernel.org> wrote: >> If we do that then I suspect the next step will be queued rwlocks :-/ The >> current rwlock_t implementation is rather primitive by modern standards. >> (We'd probably have killed rwlock_t long ago if not for the >> tasklist_lock.) > Yeah, I'm not happy about or rwlocks. That's one lock that currently > is so broken that I think we could easily argue for making that one > queued. > > Waiman had a qrwlock series that looked reasonable, and I think his > later versions were drop-in replacements (ie they automatically just > did the RightThing(tm) wrt interrupts taking a recursive read lock - I > objected to the first versions that required that to be stated > explicitly).
The latest version (v3) will allow recursive read lock in interrupt handlers.
> I think Waiman's patches (even the later ones) made the queued rwlocks > be a side-by-side implementation with the old rwlocks, and I think > that was just being unnecessarily careful. It might be useful for > testing to have a config option to switch between the two, but we > might as well go all the way.
It is not actually a side-by-side implementation. A user can choose either regular rwlock or the queue one, but never both by setting a configuration parameter. However, I now think that maybe we should do it the lockref way by pre-determining it on a per-architecture level without user visible configuration option.
-Longman
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