Hi, I've repeatedly stared at an SD flag and asked myself "how should that be set up in the domain hierarchy anyway?". I figured that if we formalize our flags zoology a bit, we could also do some runtime assertions on them - this is what this series is all about.
Patches ======= The idea is to associate the flags with metaflags that describes how they should be set in a sched domain hierarchy ("if this SD has it, all its {parents, children} have it") or how they behave wrt degeneration - details are in the comments and commit logs. The good thing is that the debugging bits go away when CONFIG_SCHED_DEBUG isn't set. The bad thing is that this replaces SD_* flags definitions with some unsavoury macros. This is mainly because I wanted to avoid having to duplicate work between declaring the flags and declaring their metaflags. o Patches 1-3 are topology cleanups / fixes o Patches 4-6 instrument SD flags and add assertions o Patches 7-10 leverage the instrumentation to factorize domain degeneration Revisions ========= v3 -> v4 -------- o Reordered the series to have fixes / cleanups first o Added SD_ASYM_CPUCAPACITY propagation (Quentin) o Made ARM revert back to the default sched topology (Dietmar) o Removed SD_SERIALIZE degeneration special case (Peter) o Made SD_NUMA and SD_SERIALIZE have SDF_NEEDS_GROUPS As discussed on v3, I thought this wasn't required, but thinking some more about it there can be cases where that changes the current behaviour. For instance, in the following wacky triangle: 0\ 30 | \ 20 | 2 | / 1/ 30 there are two unique distances thus two NUMA topology levels, however the first one for node 2 would have the same span as its child domain and thus should be degenerated. If we don't give SD_NUMA and SD_SERIALIZE SDF_NEEDS_GROUPS, this domain wouldn't be denegerated since its child *doesn't* have either SD_NUMA or SD_SERIALIZE (it's the first NUMA domain), and we'd have this weird NUMA domain lingering with a single group. v2 -> v3 -------- o Reworded comment for SD_OVERLAP (it's about the groups, not the domains) o Added more flags to the SD degeneration mask o Added generation of an SD flag mask for the degeneration functions (Peter) RFC -> v2 --------- o Rebased on top of tip/sched/core o Aligned wording of comments between flags o Rectified some flag descriptions (Morten) o Added removal of SD_SHARE_POWERDOMAIN (Morten) Valentin Schneider (10): ARM, sched/topology: Remove SD_SHARE_POWERDOMAIN ARM: Revert back to default scheduler topology. sched/topology: Propagate SD_ASYM_CPUCAPACITY upwards sched/topology: Split out SD_* flags declaration to its own file sched/topology: Define and assign sched_domain flag metadata sched/topology: Verify SD_* flags setup when sched_debug is on sched/topology: Add more flags to the SD degeneration mask sched/topology: Remove SD_SERIALIZE degeneration special case sched/topology: Introduce SD metaflag for flags needing > 1 groups sched/topology: Use prebuilt SD flag degeneration mask arch/arm/kernel/topology.c | 26 ------ include/linux/sched/sd_flags.h | 156 +++++++++++++++++++++++++++++++++ include/linux/sched/topology.h | 36 +++++--- kernel/sched/topology.c | 54 ++++++------ 4 files changed, 204 insertions(+), 68 deletions(-) create mode 100644 include/linux/sched/sd_flags.h -- 2.27.0