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  1. 17 Mar, 2023 32 commits
  3. 10 Mar, 2023 4 commits
  5. 07 Mar, 2023 1 commit
  7. 06 Mar, 2023 1 commit
    • Greg Kroah-Hartman's avatar
      driver core: remove CONFIG_SYSFS_DEPRECATED and CONFIG_SYSFS_DEPRECATED_V2 · 721da5ce
      Greg Kroah-Hartman authored 
      CONFIG_SYSFS_DEPRECATED was added in commit 88a22c98
("CONFIG_SYSFS_DEPRECATED") in 2006 to allow systems with older versions
of some tools (i.e. Fedora 3's version of udev) to boot properly.  Four
years later, in 2010, the option was attempted to be removed as most of
userspace should have been fixed up properly by then, but some kernel
developers clung to those old systems and refused to update, so we added
CONFIG_SYSFS_DEPRECATED_V2 in commit e52eec13 ("SYSFS: Allow boot
time switching between deprecated and modern sysfs layout") to allow
them to continue to boot properly, and we allowed a boot time parameter
to be used to switch back to the old format if needed.

Over time, the logic that was covered under these config options was
slowly removed from individual driver subsystems successfully, removed,
and the only thing that is now left in the kernel are some changes in
the block layer's representation in sysfs where real directories are
used instead of symlinks like normal.

Because the original changes were done to userspace tools in 2006, and
all distros that use those tools are long end-of-life, and older
non-udev-based systems do not care about the block layer's sysfs
representation, it is time to finally remove this old logic and the
config entries from the kernel.

Cc: Jonathan Corbet <corbet@lwn.net>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: linux-block@vger.kernel.org
Cc: linux-doc@vger.kernel.org
Acked-by: default avatarJens Axboe <axboe@kernel.dk>
Link: https://lore.kernel.org/r/20230223073326.2073220-1-gregkh@linuxfoundation.orgSigned-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
      721da5ce
  9. 05 Mar, 2023 2 commits
    • Linus Torvalds's avatar
      Linux 6.3-rc1 · fe15c26e
      Linus Torvalds authored
      fe15c26e
    • Linus Torvalds's avatar
      cpumask: re-introduce constant-sized cpumask optimizations · 596ff4a0
      Linus Torvalds authored 
      Commit aa47a7c2 ("lib/cpumask: deprecate nr_cpumask_bits") resulted
in the cpumask operations potentially becoming hugely less efficient,
because suddenly the cpumask was always considered to be variable-sized.

The optimization was then later added back in a limited form by commit
6f9c07be ("lib/cpumask: add FORCE_NR_CPUS config option"), but that
FORCE_NR_CPUS option is not useful in a generic kernel and more of a
special case for embedded situations with fixed hardware.

Instead, just re-introduce the optimization, with some changes.

Instead of depending on CPUMASK_OFFSTACK being false, and then always
using the full constant cpumask width, this introduces three different
cpumask "sizes":

 - the exact size (nr_cpumask_bits) remains identical to nr_cpu_ids.

   This is used for situations where we should use the exact size.

 - the "small" size (small_cpumask_bits) is the NR_CPUS constant if it
   fits in a single word and the bitmap operations thus end up able
   to trigger the "small_const_nbits()" optimizations.

   This is used for the operations that have optimized single-word
   cases that get inlined, notably the bit find and scanning functions.

 - the "large" size (large_cpumask_bits) is the NR_CPUS constant if it
   is an sufficiently small constant that makes simple "copy" and
   "clear" operations more efficient.

   This is arbitrarily set at four words or less.

As a an example of this situation, without this fixed size optimization,
cpumask_clear() will generate code like

        movl    nr_cpu_ids(%rip), %edx
        addq    $63, %rdx
        shrq    $3, %rdx
        andl    $-8, %edx
        callq   memset@PLT

on x86-64, because it would calculate the "exact" number of longwords
that need to be cleared.

In contrast, with this patch, using a MAX_CPU of 64 (which is quite a
reasonable value to use), the above becomes a single

	movq $0,cpumask

instruction instead, because instead of caring to figure out exactly how
many CPU's the system has, it just knows that the cpumask will be a
single word and can just clear it all.

Note that this does end up tightening the rules a bit from the original
version in another way: operations that set bits in the cpumask are now
limited to the actual nr_cpu_ids limit, whereas we used to do the
nr_cpumask_bits thing almost everywhere in the cpumask code.

But if you just clear bits, or scan for bits, we can use the simpler
compile-time constants.

In the process, remove 'cpumask_complement()' and 'for_each_cpu_not()'
which were not useful, and which fundamentally have to be limited to
'nr_cpu_ids'.  Better remove them now than have somebody introduce use
of them later.

Of course, on x86-64 with MAXSMP there is no sane small compile-time
constant for the cpumask sizes, and we end up using the actual CPU bits,
and will generate the above kind of horrors regardless.  Please don't
use MAXSMP unless you really expect to have machines with thousands of
cores.
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      596ff4a0
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