linux-kernel - Re: [PATCH tip/core/rcu 1/4] mce: Stop using array-index-based RCU primitives

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Message-ID: <20150513125106.GV6776@linux.vnet.ibm.com>
Date:	Wed, 13 May 2015 05:51:06 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Borislav Petkov <bp@...en8.de>
Cc:	linux-kernel@...r.kernel.org, mingo@...nel.org,
	laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
	josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
	rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
	dvhart@...ux.intel.com, fweisbec@...il.com, oleg@...hat.com,
	bobby.prani@...il.com, linux-edac@...r.kernel.org,
	Tony Luck <tony.luck@...el.com>
Subject: Re: [PATCH tip/core/rcu 1/4] mce: Stop using array-index-based RCU
 primitives

On Wed, May 13, 2015 at 12:31:57PM +0200, Borislav Petkov wrote:
> On Tue, May 12, 2015 at 02:18:41PM -0700, Paul E. McKenney wrote:
> > From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
> > 
> > Because mce is arch-specific x86 code, there is little or no
> > performance benefit of using rcu_dereference_index_check() over using
> > smp_load_acquire().  It also turns out that mce is the only place that
> > array-index-based RCU is used, and it would be convenient to drop
> > this portion of the RCU API.
> > 
> > This patch therefore changes rcu_dereference_index_check() uses to
> > smp_load_acquire(), but keeping the lockdep diagnostics, and also
> > changes rcu_access_index() uses to READ_ONCE().
> > 
> > Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> > Cc: linux-edac@...r.kernel.org
> > Cc: Tony Luck <tony.luck@...el.com>
> > Cc: Borislav Petkov <bp@...en8.de>
> 
> Looks good to me.
> 
> If it is easier for you carrying it in your tree:
> 
> Acked-by: Borislav Petkov <bp@...e.de>
> 
> Otherwise, let me know.

Thank you, I have applied your Acked-by.  Probably easier for me
to carry this change, given that it needs to be applied before the
later patches that remove array-index support from RCU.


							Thanx, Paul

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