linux-kernel - Re: [PATCH 2/2] locking/rwsem: Use a return variable in rwsem_spin_on

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Date:	Thu, 09 Apr 2015 12:59:37 -0700
From:	Davidlohr Bueso <dave@...olabs.net>
To:	Jason Low <jason.low2@...com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Tim Chen <tim.c.chen@...ux.intel.com>,
	Aswin Chandramouleeswaran <aswin@...com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] locking/rwsem: Use a return variable in
 rwsem_spin_on_owner()

On Thu, 2015-04-09 at 12:43 -0700, Jason Low wrote:
> So that looks more similar to how the original code was where the
> rcu_read_lock() and rcu_read_unlock() was done inside the owner_running
> helper function (though without the CONFIG_DEBUG_PAGEALLOC), before
> commit 307bf9803f25 ("sched: Simplify mutex_spin_on_owner()") modified
> it to be done outside the loop.

I think this is why Linus was mentioning the CONFIG_PREEMPT_RCU case as
well, so taking and releasing the read lock in those cases in the loop
would actually hurt more.

Thanks,
Davidlohr

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