On 06/17/2010 06:02 PM, Arjan van de Ven wrote: > On Thu, 17 Jun 2010 17:54:48 +0200 > Tejun Heo <tj@xxxxxxxxxx> wrote: > >> Crazy devices too but I think they would >> fall in a single tick any way. > > not sure what ticks have to do with anything but ok ;) Eh... right, I was thinking about something else. IRQ expect code originally had a tick based duration estimator to determine poll interval which I ripped out later for simpler stepped adjustments. c-state would need higher frequency timing measurements than jiffies. >> At any rate, let's say I have those >> numbers, how would I feed it into c-state selection? > > if we have this, we need to put a bit of glue in the backend that > tracks (per cpu I suppose) the shortest expected interrupt, which > the C state code then queries. > (and in that regard, it does not matter if shortest expected is > computed via heuristic on a per irq basis, or passed in). > > mapping an irq to a cpu is not a 100% science (since interrupts can > move in theory), but just assuming that the irq will happen on the same > CPU it happened last time is more than good enough. Hmmm... the thing is that there will be many cases which won't fit irq_expect() model (why irq_watch() exists in the first place) and for the time being libata is the only one providing that data. Would the data still be useful to determine which c-state to use? Thanks. -- tejun -- To unsubscribe from this list: send the line "unsubscribe linux-ide" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
