Messages in this thread | | | Date | Sat, 28 Sep 2013 12:33:36 -0700 | Subject | Re: [PATCH] rwsem: reduce spinlock contention in wakeup code path | From | Linus Torvalds <> |
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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).
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.
The old rwlock's really have been a disappointment - they are slower than spinlocks, and seldom/never end up scaling any better. Their main advantage was literally the irq behavior - allowing readers to happen without the expense of worrying about irq's.
Linus
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