On 6 January 2014 17:21, Peter Zijlstra peterz@infradead.org wrote:
On Wed, Dec 18, 2013 at 02:13:51PM +0100, Vincent Guittot wrote:
This patch applies on top of the two patches [1][2] that have been proposed by Peter for creating a new way to initialize sched_domain. It includes some minor compilation fixes and a trial of using this new method on ARM platform. [1] https://lkml.org/lkml/2013/11/5/239 [2] https://lkml.org/lkml/2013/11/5/449
Based on the results of this tests, my feeling about this new way to init the sched_domain is a bit mitigated.
Yay :-)
We can add more levels that will describe other dependency/independency like the frequency scaling dependency and as a result the final sched_domain topology will have additional levels (if they have not been removed during the degenerate sequence)
Yeah, this 'creative' use of degenerate domains is pretty neat ;-)
thanks :-)
My concern is about the configuration of the table that is used to create the sched_domain. Some levels are "duplicated" with different flags configuration which make the table not easily readable and we must also take care of the order because parents have to gather all cpus of its childs. So we must choose which capabilities will be a subset of the other one. The order is almost straight forward when we describe 1 or 2 kind of capabilities (package ressource sharing and power sharing) but it can become complex if we want to add more.
I think I see what you're saying, although I hope that won't actually happen in real hardware -- that said, people do tend to do crazy with these ARM chips :/
it should be ok for ARM chip because the cores in a cluster share the same clock but it doesn't mean that it will not be possible in a near future or on other arch.
We should also try and be conservative in the topology flags we want to add, which should further reduce the amount of pain here.
yes, i see a interest for powerdomain sharing and clock sharing flags so it should minimize the complexity
For now I do think this is a viable approach.. Yes its a bit cumbersome for these asymmetric systems but it does give us enough to start playing.
ok
Vincent
I yet have to read Morton's emails on the P and C states, will try to have a look at those tomorrow with a hopefully fresher brain -- somehow its the end of the day already..