[PATCH 3.18-rc3 v9 1/5] irqchip: gic: Finer grain locking for gic_raise_softirq

Stephen Boyd sboyd at codeaurora.org
Tue Nov 25 17:27:38 PST 2014

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.

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