linux-kernel - [PATCH v3 0/7] sched: Instrument sched domain flags

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Message-Id: <20200701190656.10126-1-valentin.schneider@arm.com>
Date:   Wed,  1 Jul 2020 20:06:48 +0100
From:   Valentin Schneider <valentin.schneider@....com>
To:     linux-kernel@...r.kernel.org
Cc:     mingo@...nel.org, peterz@...radead.org, vincent.guittot@...aro.org,
        dietmar.eggemann@....com, morten.rasmussen@....com
Subject: [PATCH v3 0/7] sched: Instrument sched domain flags

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 1-2 set up the SD flag definition groundwork
o Patch 3 enables the hierarchy debugging
o Patch 4 is a derelict SD flag removal
o Patches 5-7 tweak the SD degeneration to leverage metaflags as well (suggested
  by Peter).

  Note that this builds a compile-time mask using the single most horrendous
  macro I have ever presented to the public eye. It might end up being much
  better to explicitely build the mask in topology.h, but to be honest I felt
  like I had to show that monster around out of morbid fascination.

Revisions
=========

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 (7):
  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
  arm, sched/topology: Remove SD_SHARE_POWERDOMAIN
  sched/topology: Add more flags to the SD degeneration mask
  sched/topology: Introduce SD metaflag for flags needing > 1 groups
  sched/topology: Use prebuilt SD flag degeneration mask

 arch/arm/kernel/topology.c     |   2 +-
 include/linux/sched/sd_flags.h | 153 +++++++++++++++++++++++++++++++++
 include/linux/sched/topology.h |  36 +++++---
 kernel/sched/topology.c        |  40 +++++----
 4 files changed, 197 insertions(+), 34 deletions(-)
 create mode 100644 include/linux/sched/sd_flags.h

--
2.27.0