On Mon, Jan 7, 2013 at 8:34 PM, Tejun Heo firstname.lastname@example.org wrote:
On Mon, Jan 07, 2013 at 03:28:33PM +0530, Viresh Kumar wrote:
Firstly the root cause of this patchset.
Myself and some others in Linaro are working on ARM future cores: big.LITTLE systems. Here we have few very powerful, high power consuming cores (big, currently A15's) and few very efficient ones (LITTLE, currently A7's).
The ultimate goal is to save as much power as possible without compromising much with performance. For, that we wanted most of the stuff to run on LITTLE cores and some performance-demanding stuff on big Cores. There are multiple things going around in this direction. Now, we thought A15's or big cores shouldn't be used for running small tasks like timers/workqueues and hence this patch is an attempt towards reaching that goal.
I see. My understanding of big.little is very superficial so there are very good chances that I'm utterly wrong, but to me it seems like more of a stop-gap solution than something which will have staying power in the sense that the complexity doesn't seem to have any inherent reason other than the failure to make the big ones power efficient enough while idle or under minor load.
The two processors use different manufacturing processes - one optimised for performance, the other for really low power. So the reason is physics at this point. Other architectures are known to be playing with similar schemes. ARM's big.LITTLE is just the first one to the market.
Maybe this isn't specific to big.little and heterogeneous cores will be the way of future with big.little being just a forefront of the trend. And even if that's not the case, it definitely doesn't mean that we can't accomodate big.little, but, at this point, it does make me a bit more reluctant to make wholesale changes specifically for big.little.
The patches aren't targeted to benefit only b.L systems though it was definitely the trigger for our investigations. Our hope is that after presenting more analysis results from our side we'll be able to convince the community of the general usefulness of this feature.
Here are a few short introductions to big.LITTLE in case you're interested.