On Fri, Nov 02, 2018 at 08:58:39PM +0200, Nick Kossifidis wrote: > Hello All, > > Στις 2018-11-02 01:04, Atish Patra έγραψε: > > This patch series adds the cpu topology for RISC-V. It contains > > both the DT binding and actual source code. It has been tested on > > QEMU & Unleashed board. > > > > The idea is based on cpu-map in ARM with changes related to how > > we define SMT systems. The reason for adopting a similar approach > > to ARM as I feel it provides a very clear way of defining the > > topology compared to parsing cache nodes to figure out which cpus > > share the same package or core. I am open to any other idea to > > implement cpu-topology as well. > > > > I was also about to start a discussion about CPU topology on RISC-V > after the last swtools group meeting. The goal is to provide the > scheduler with hints on how to distribute tasks more efficiently > between harts, by populating the scheduling domain topology levels > (https://elixir.bootlin.com/linux/v4.19/ident/sched_domain_topology_level). > What we want to do is define cpu groups and assign them to > scheduling domains with the appropriate SD_ flags > (https://github.com/torvalds/linux/blob/master/include/linux/sched/topology.h#L16). > OK are we defining a CPU topology binding for Linux scheduler ? NACK for all the approaches that assumes any knowledge of OS scheduler. > So the cores that belong to a scheduling domain may share: > CPU capacity (SD_SHARE_CPUCAPACITY / SD_ASYM_CPUCAPACITY) > Package resources -e.g. caches, units etc- (SD_SHARE_PKG_RESOURCES) > Power domain (SD_SHARE_POWERDOMAIN) > Too Linux kernel/scheduler specific to be part of $subject > In this context I believe using words like "core", "package", > "socket" etc can be misleading. For example the sample topology you > use on the documentation says that there are 4 cores that are part > of a package, however "package" has a different meaning to the > scheduler. Also we don't say anything in case they share a power > domain or if they have the same capacity or not. This mapping deals > only with cache hierarchy or other shared resources. > {Un,}fortunately those are terms used by hardware people. > How about defining a dt scheme to describe the scheduler domain > topology levels instead ? e.g: > NACK as already mentioned above. -- Regards, Sudeep
