Messages in this thread | | | From | Valentin Schneider <> | Subject | [PATCH v5 00/17] sched: Instrument sched domain flags | Date | Wed, 12 Aug 2020 13:52:43 +0100 |
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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. Conceptually they are pretty close to the macros used for SCHED_FEAT.
o Patches 1-2 remove a derelict flag and align the arm scheduler topology with arm64's o Patches 3-8 instrument SD flags with metadata and add assertions o Patches 9-10 are additional topology cleanups o Patches 11-16 each add a new flag to SD_DEGENERATE_GROUPS_MASK o Patch 17 leverage the previous 6 patches to further factorize domain degeneration
Revisions =========
v4 -> v5 --------
The final git diff between v4 and v5 isn't too big; there is no diff on the domain degeneration side of things, it has just been split up in more patches.
o Shuffled the series around to facilitate bisection (Ingo) I kept the arm bits at the start because that was a bit simpler, and in the unlikely case that needs to be reverted it won't be too hard. o Split the degeneration mask tweak into individual commits per new flag (Ingo) o Collected Reviewed-by from Dietmar; since I shuffled the whole lot I didn't keep your Tested-by, sorry!
o Turned the SD flags into an enum with automagic power of 2 assignment. I poked the dwarves and they assured me the SD flag values haven't changed. o [new patch] Made SD flag debug file output flag names
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 (17): ARM, sched/topology: Remove SD_SHARE_POWERDOMAIN ARM: Revert back to default scheduler topology. 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/debug: Output SD flag names rather than their values sched/topology: Introduce SD metaflag for flags needing > 1 groups sched/topology: Use prebuilt SD flag degeneration mask sched/topology: Remove SD_SERIALIZE degeneration special case sched/topology: Propagate SD_ASYM_CPUCAPACITY upwards sched/topology: Mark SD_PREFER_SIBLING as SDF_NEEDS_GROUPS sched/topology: Mark SD_BALANCE_WAKE as SDF_NEEDS_GROUPS sched/topology: Mark SD_SERIALIZE as SDF_NEEDS_GROUPS sched/topology: Mark SD_ASYM_PACKING as SDF_NEEDS_GROUPS sched/topology: Mark SD_OVERLAP as SDF_NEEDS_GROUPS sched/topology: Mark SD_NUMA as SDF_NEEDS_GROUPS sched/topology: Expand use of SD_DEGENERATE_GROUPS_MASK to flags not needing groups
arch/arm/kernel/topology.c | 26 ------ include/linux/sched/sd_flags.h | 156 +++++++++++++++++++++++++++++++++ include/linux/sched/topology.h | 45 +++++++--- kernel/sched/debug.c | 53 ++++++++++- kernel/sched/topology.c | 54 ++++++------ 5 files changed, 265 insertions(+), 69 deletions(-) create mode 100644 include/linux/sched/sd_flags.h
-- 2.27.0
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