Messages in this thread |  | | Date | Tue, 07 Jan 2014 15:10:21 +0530 | From | Preeti U Murthy <> | Subject | Re: [RFC] sched: CPU topology try |
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Hi Vincent, Peter,
On 12/18/2013 06:43 PM, 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. > > The good point is that I have been able to create the same sched_domain > topologies than before and even more complex ones (where a subset of the cores > in a cluster share their powergating capabilities). I have described various > topology results below. > > I use a system that is made of a dual cluster of quad cores with hyperthreading > for my examples. > > If one cluster (0-7) can powergate its cores independantly but not the other > cluster (8-15) we have the following topology, which is equal to what I had > previously: > > CPU0: > domain 0: span 0-1 level: SMT > flags: SD_SHARE_CPUPOWER | SD_SHARE_PKG_RESOURCES | SD_SHARE_POWERDOMAIN > groups: 0 1 > domain 1: span 0-7 level: MC > flags: SD_SHARE_PKG_RESOURCES > groups: 0-1 2-3 4-5 6-7 > domain 2: span 0-15 level: CPU > flags: > groups: 0-7 8-15 > > CPU8 > domain 0: span 8-9 level: SMT > flags: SD_SHARE_CPUPOWER | SD_SHARE_PKG_RESOURCES | SD_SHARE_POWERDOMAIN > groups: 8 9 > domain 1: span 8-15 level: MC > flags: SD_SHARE_PKG_RESOURCES | SD_SHARE_POWERDOMAIN > groups: 8-9 10-11 12-13 14-15 > domain 2: span 0-15 level CPU > flags: > groups: 8-15 0-7 > > We can even describe some more complex topologies if a susbset (2-7) of the > cluster can't powergate independatly: > > CPU0: > domain 0: span 0-1 level: SMT > flags: SD_SHARE_CPUPOWER | SD_SHARE_PKG_RESOURCES | SD_SHARE_POWERDOMAIN > groups: 0 1 > domain 1: span 0-7 level: MC > flags: SD_SHARE_PKG_RESOURCES > groups: 0-1 2-7 > domain 2: span 0-15 level: CPU > flags: > groups: 0-7 8-15 > > CPU2: > domain 0: span 2-3 level: SMT > flags: SD_SHARE_CPUPOWER | SD_SHARE_PKG_RESOURCES | SD_SHARE_POWERDOMAIN > groups: 0 1 > domain 1: span 2-7 level: MC > flags: SD_SHARE_PKG_RESOURCES | SD_SHARE_POWERDOMAIN > groups: 2-7 4-5 6-7 > domain 2: span 0-7 level: MC > flags: SD_SHARE_PKG_RESOURCES > groups: 2-7 0-1 > domain 3: span 0-15 level: CPU > flags: > groups: 0-7 8-15 > > In this case, we have an aditionnal sched_domain MC level for this subset (2-7) > of cores so we can trigger some load balance in this subset before doing that > on the complete cluster (which is the last level of cache in my example) > > 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) > > 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.
What if we want to add arch specific flags to the NUMA domain? Currently with Peter's patch:https://lkml.org/lkml/2013/11/5/239 and this patch, the arch can modify the sd flags of the topology levels till just before the NUMA domain. In sd_init_numa(), the flags for the NUMA domain get initialized. We need to perhaps call into arch here to probe for additional flags?
Thanks
Regards Preeti U Murthy > > Regards > Vincent >
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