linux-kernel - [PATCH v2 0/5] cpumask: cleanup nr_cpu_ids vs nr_cpumask

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Date:   Mon,  5 Sep 2022 16:08:15 -0700
From:   Yury Norov <yury.norov@...il.com>
To:     linux-kernel@...r.kernel.org
Cc:     Yury Norov <yury.norov@...il.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Valentin Schneider <vschneid@...hat.com>,
        Sander Vanheule <sander@...nheule.net>,
        Alexey Klimov <klimov.linux@...il.com>,
        Eric Biggers <ebiggers@...gle.com>
Subject: [PATCH v2 0/5] cpumask: cleanup nr_cpu_ids vs nr_cpumask_bits mess

cpumask subsystem uses nr_cpu_ids and nr_cpumask_bits interchangeably
despite that the variables have different meaning and purpose. It makes
some cpumask functions broken.

This series cleans that mess and adds new config FORCE_NR_CPUS that
allows to optimize cpumask subsystem if the number of CPUs is known
at compile-time.

After some testing I found build broken when SMP is on and NR_CPUS == 1.
This is addressed in a new patch #1, and in the following patch #2 that
now declares set_nr_cpu_ids in cpumask.h (was in smp.h).

v1: https://lore.kernel.org/lkml/20220829165748.1008477-1-yury.norov@gmail.com/T/#mecbd787f8d1bff1454a4ec2fe46ad6dc168df695
v2:
 - don't declare nr_cpu_ids if NR_CPUS == 1;
 - move set_nr_cpu_ids() from smp.h to cpumask.h to avoid errors in some
   inclusion paths;
 - drop 'default n' in FORCE_NR_CPUS option description;
 - rebase on top of v6.0-rc4.

Yury Norov (5):
  smp: don't declare nr_cpu_ids if NR_CPUS == 1
  smp: add set_nr_cpu_ids()
  lib/cpumask: delete misleading comment
  lib/cpumask: deprecate nr_cpumask_bits
  lib/cpumask: add FORCE_NR_CPUS config option

 arch/loongarch/kernel/setup.c |  2 +-
 arch/mips/kernel/setup.c      |  2 +-
 arch/x86/kernel/smpboot.c     |  4 ++--
 arch/x86/xen/smp_pv.c         |  2 +-
 include/linux/cpumask.h       | 22 +++++++++++-----------
 kernel/smp.c                  |  6 ++++--
 lib/Kconfig                   |  9 +++++++++
 7 files changed, 29 insertions(+), 18 deletions(-)

-- 
2.34.1