Re: [PATCH] rwsem: reduce spinlock contention in wakeup code path

From: Andi Kleen
Date: Sat Sep 28 2013 - 15:14:09 EST

> Of course, since then, we may well have screwed things up and now we
> sleep under it, but I still really think it was a mistake to do it in
> the first place.
> So if the primary reason for this is really just that f*cking anon_vma
> lock, then I would seriously suggest:
> - turn it back into a spinlock (or rwlock_t, since we subsequently
> separated the read and write paths)

Yes please. spinlocks/rwlocks have so much nicer performance behavior than
rwsems/mutexes (which noone seems to fully understand)

We had also significant performance regressions from every such
spinning->sleeping change in the VM (this was just the latest)

And afaik anon_vma is usually hold short.


ak@xxxxxxxxxxxxxxx -- Speaking for myself only.
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