On 1 January 2014 06:00, Preeti U Murthy <pre...@linux.vnet.ibm.com> wrote: > Hi Vincent, > > 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) > > The design looks good to me. In my opinion information like P-states and > C-states dependency can be kept separate from the topology levels, it > might get too complicated unless the information is tightly coupled to > the topology. > >> >> 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 > > I do not feel this is a problem since the levels are not duplicated, > rather they have different properties within them which is best > represented by flags like you have introduced in this patch. > >> 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 > > The sched domain levels which have SD_SHARE_POWERDOMAIN set is expected > to have cpus which are a subset of the cpus that this domain would have > included had this flag not been set. In addition to this every higher > domain, irrespective of SD_SHARE_POWERDOMAIN being set, will include all > cpus of the lower domains. As far as I see, this patch does not change > these assumptions. Hence I am unable to imagine a scenario when the > parent might not include all cpus of its children domain. Do you have > such a scenario in mind which can arise due to this patch ?
My patch doesn't have issue because i have added only 1 layer which is always a subset of the current cache level topology but if we add another feature with another layer, we have to decide which feature will be a subset of the other one. Vincent > > Thanks > > Regards > Preeti U Murthy > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/