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
As far as I can see, no follo-ups happened.
Nicolas