linux-kernel - Re: [PATCH 3/6] locking/rwsem: Set lock ownership ASAP

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Date:	Tue, 27 Jan 2015 18:10:21 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Davidlohr Bueso <dave@...olabs.net>
Cc:	Ingo Molnar <mingo@...nel.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Jason Low <jason.low2@...com>,
	Michel Lespinasse <walken@...gle.com>,
	Tim Chen <tim.c.chen@...ux.intel.com>,
	linux-kernel@...r.kernel.org, Davidlohr Bueso <dbueso@...e.de>
Subject: Re: [PATCH 3/6] locking/rwsem: Set lock ownership ASAP

On Sun, Jan 25, 2015 at 11:36:06PM -0800, Davidlohr Bueso wrote:
> In order to optimize the spinning step, we need to set the lock
> owner as soon as the lock is acquired; after a successful counter
> cmpxchg operation, that is. This is particularly useful as rwsems
> need to set the owner to nil for readers, so there is a greater
> chance of falling out of the spinning. Currently we only set the
> owner much later in the game, in the more generic level -- latency
> can be specially bad when waiting for a node->next pointer when
> releasing the osq in up_write calls.
> 
> As such, update the owner inside rwsem_try_write_lock (when the
> lock is obtained after blocking) and rwsem_try_write_lock_unqueued
> (when the lock is obtained while spinning). This requires creating
> a new internal rwsem.h header to share the owner related calls.
> 
> Also cleanup some headers for mutex and rwsem.

This is the thing I suggested
lkml.kernel.org/r/20150108103708.GE29390@...ns.programming.kicks-ass.net
there right?

Do you have numbers for how much this gained?
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