linux-kernel - Re: [PATCH 3.18-rc3 v9 1/5] irqchip: gic: Finer grain locking for gic_raise

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Date:	Tue, 25 Nov 2014 17:27:38 -0800
From:	Stephen Boyd <sboyd@...eaurora.org>
To:	Daniel Thompson <daniel.thompson@...aro.org>
CC:	Nicolas Pitre <nicolas.pitre@...aro.org>,
	Marc Zyngier <marc.zyngier@....com>,
	"linaro-kernel@...ts.linaro.org" <linaro-kernel@...ts.linaro.org>,
	Russell King <linux@....linux.org.uk>,
	Jason Cooper <jason@...edaemon.net>,
	"patches@...aro.org" <patches@...aro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Daniel Drake <drake@...lessm.com>,
	Dmitry Pervushin <dpervushin@...il.com>,
	Dirk Behme <dirk.behme@...bosch.com>,
	John Stultz <john.stultz@...aro.org>,
	Tim Sander <tim@...eglstein.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Sumit Semwal <sumit.semwal@...aro.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 3.18-rc3 v9 1/5] irqchip: gic: Finer grain locking for
 gic_raise_softirq

On 11/25/2014 01:10 PM, Daniel Thompson wrote:
> On 25/11/14 20:17, Nicolas Pitre wrote:
>> On Tue, 25 Nov 2014, Marc Zyngier wrote:
>>
>>> Hi Daniel,
>>>
>>> On 25/11/14 17:26, Daniel Thompson wrote:
>>>> irq_controller_lock is used for multiple purposes within the gic driver.
>>>> Primarily it is used to make register read-modify-write sequences atomic.
>>>> It is also used by gic_raise_softirq() in order that the big.LITTLE
>>>> migration logic can figure out when it is safe to migrate interrupts
>>>> between physical cores.
>>>>
>>>> The second usage of irq_controller_lock is difficult to discern when
>>>> reviewing the code because the migration itself takes place outside
>>>> the lock.
>>>>
>>>> This patch makes the second usage more explicit by splitting it out into
>>>> a separate lock and providing better comments.
>>> While we're at it, how about an additional patch that would make this
>>> lock disappear entirely when the big-little stuff is not compiled in,
>>> which is likely to be the case on a lot of (dare I say most?) systems?
>>> That will save expensive barriers that we definitely could do without.
>> For the record, I reviewed and ACKed a patch doing exactly that a while
>> ago:
>>
>> http://lkml.org/lkml/2014/8/13/486
> Well remembered! That patch had a different motivation but is very
> similar to mine... so much so I might steal bit of it.
>
> I'll make sure I put Stephen on Cc: when I respin with the changes Marc
> requested.

I don't get a random Cc here? :-)

Anyway, yes please let's merge that patch.

-- 
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
a Linux Foundation Collaborative Project

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