linux-kernel - Re: [RFC][PATCH 0/5] Optimize percpu-rwsem

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Date:	Tue, 26 May 2015 11:42:11 -0700
From:	Davidlohr Bueso <dave@...olabs.net>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>,
	Tejun Heo <tj@...nel.org>, Ingo Molnar <mingo@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	der.herr@...r.at
Subject: Re: [RFC][PATCH 0/5] Optimize percpu-rwsem

On Tue, 2015-05-26 at 11:12 -0700, Linus Torvalds wrote:
> On Tue, May 26, 2015 at 4:43 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> >
> > This is a derived work of the cpu hotplug lock rework I did in 2013 which never
> > really went anywhere because Linus didn't like it.
> >
> > This applies those same optimizations to the percpu-rwsem. Seeing how we did
> > all the work it seemed a waste to not use it at all.
> 
> So I *still* don't like it.
> 
> We literally have one single percpu-rwsem IN THE WHOLE KERNEL TREE.
> 
> One.
> 
> Not "a couple". Not "hundreds". ONE.

Instead of dropping percpu-rwsem, I was thinking we could instead look
for opportunities to convert new users, for instance shinkers, where the
write lock is also taken just for register and unregister purposes,
similar to uprobes.

Thanks,
Davidlohr

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