On Mon, Jul 29, 2013 at 02:36:30PM +0100, Dave Martin wrote: > On Mon, Jul 29, 2013 at 10:54:01AM +0100, Will Deacon wrote: > > On Mon, Jul 29, 2013 at 10:46:06AM +0100, Vincent Guittot wrote: > > > On 27 July 2013 12:42, Hanjun Guo <hanjun....@linaro.org> wrote: > > > > Power aware scheduling needs the cpu topology information to improve the > > > > cpu scheduler decision making. > > > > > > It's not only power aware scheduling. The scheduler already uses > > > topology and cache sharing when CONFIG_SCHED_MC and/or > > > CONFIG_SCHED_SMT are enable. So you should also add these configs for > > > arm64 so the scheduler can use it > > > > ... except that the architecture doesn't define what the AFF fields in MPIDR > > really represent. Using them to make key scheduling decisions relating to > > In fact, the ARM Architecture doesn't place any requirements on MPIDRs to > force the aff fields to exist _at all_. It's just a recommendation. > Instead, you have a 24 or 32-bit number which is unique per CPU, and which > is _probably_ assigned in a way resembling the aff fields. > > > cache proximity seems pretty risky to me, especially given the track record > > we've seen already on AArch32 silicon. It's a convenient register if it > > contains the data we want it to contain, but we need to force ourselves to > > come to terms with reality here and simply use it as an identifier for a > > CPU. > > +1 > > Also, we should align arm and arm64. The problem is basically exactly > the same, and the solution needs to be the same. struct cputopo_arm is > already being abused -- for example, TC2 describes the A15 and A7 > clusters on a single die as having different "socket_id" values, even > though this is obviously nonsense. But there's no other way to describe > that system today. > > > Can't we just use the device-tree to represent this topological data for > > arm64? Lorenzo has been working on bindings in this area. > > This may become more important as we start to see things like asymmetric > topologies appearing (different numbers of nodes and different > interdependence characteristics in adjacent branches of the topology > etc.)
Will and Dave summed up the existing issues with MPIDR definition related to the topology description. FYI, a link to the current topology bindings posted on DT-discuss and LAKML: https://lists.ozlabs.org/pipermail/devicetree-discuss/2013-April/031725.html I am waiting for the dust to settle on the DT bindings review discussions to repost them and get them finalized. Lorenzo -- 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/