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. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
