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    Subject[PATCH v5 00/17] sched: Instrument sched domain flags
    Date
    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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