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Subject[PATCH mask 0/15] bitmap and cpumask cleanup
					Paul Jackson
pj@sgi.com
6 May 2004

Bitmap and Cpumask Cleanup

Andrew,

Please consider the following patch set for your *-mm patches.

It removes some 27 kernel source files, simplifies cpumasks,
and in the colorful language of Rusty, it gets rid of such
headers as:

asm-generic/cpumask_optimized_for_large_smp_with_sparse_array_and_small_stack.h

It also forms the basis for a nodemask_t patch, that is
awaiting in the wings, from Matthew Dobson.

Each patch is described below, in "Patch Details."

===

This is the fifth version of my cleanup of bitmaps and cpumasks.

This set of nine patches applies against 2.6.6-rc3-mm2 plus six
optional fixup patches, also included.

The actual patches will be posted in another hour or two, as
followups to this initial post.

Primay goals:

The primary goal of this patch set is to simplify the code for
cpumask_t and (later) nodemask_t, make them easier to use, and
reduce code duplication.

Several flavors of cpumask have been reduced to one, with some
local special handling to optimize for that vast majority of
systems which have less than 32 (or 64) CPUs.

The bitmap operations upon which cpumasks depend have been
optimized a bit more, with a more careful mix of inline and
outofline code.

By simplifying masks to a single file, it should also be
easier to add other such mask types, such as the nodemask
that Matthew Dobson has waiting in the wings, just by
copying cpumask.h and making a few global edits.

There is no significant difference between this fifth version
and the fourth version of April 21, 2004. The basis for the
patch has been moved forward to 2.6.6-rc3-mm2. And a few
of the more trivial patches in the set have been collapsed,
reducing the patchset to 9 patches.

What's new (comparing 2.6.6-rc3-mm2 to this patch set):
1) Some 27 files matching the pattern include/*/*mask*.h
are replaced with the single file include/linux/cpumask.h
The variety of arch-specific redirect headers for various
cpumask implementation flavors is gone.
2) The bitmap operations (bitmap.h, bitmap.c) are optimized
for systems of less than 32 (or 64) CPUs.
3) The cpumask operations are now just a thin layer on top
of the bitmask and a few other operations. A cpumask is a
bitmask of exactly NR_CPUS bits, wrapped in a structure.
4) bitmap_complement and cpumask_complement now take two args,
source and target, instead of working in place.
5) Some uses of these macros elsewhere in the kernel were fine
tuned.
6) On ia64, find_first_bit and find_first_zero_bit are
uninlined - saving quite a bit of kernel text space.
The architectures: alpha, parisc, ppc, sh, sparc, sparc64
have this same bit find code, and might also want to uninline.
7) Comments in bitmap.h and cpumask.h list available ops for ease
of browsing.
8) The MASK_ALL macro zeros out unused bits on multiword bitmaps.
9) This patch includes Bill Irwin's recent rewrite of the
bitmap_shift operators to avoid assuming some fixed upper
bound on bitmap sizes.
10) A few more mask macros have been added, to make it easier to
code mask manipulations correctly and easily. They provide
xor, andnot, intersects and subset operators.
Bug fixes:
1) *_complement macros don't leave unused high bits set
2) MASK_ALL for sizes > 1 word, but not exact word multiple,
doesn't have unused high bits set
3) Explicit, documented semantics for handling these unused high bits.
4) A few missing const attributes in bitmap & bitops added.
5) The (Hamming) cpumask weight macros were using the bitops hweight*()
macros, which don't mask high unused bits - fixed to use the bitmap
weight macro which does this masking.
Do to the rather limited use so far of cpumask macros, I am
not aware of anything that these bugs would actually break in
current mm or linus kernels.

Testing so far:
Kernels have been built for i386 (SMP and not), sparc64 and
ia64 (sn2_defconfig), and booted and minimally tested on SN2.
Kernel text size has been compared and found to typically
get a little smaller. Correct function of bit operations
has been tested for a variety of NR_CPUS values in a user
level framework, using gcc compiler versions 2.95.3, 3.2.3 and
3.3.2. Joe Korty has built and booted on Opteron.

Reviews and feedback:
This code has been sent to the arch maintainers, and has been
reviewed in some form or other by several, including:
- William Lee Irwin III <wli@holomorphy.com>
- Jesse Barnes <jbarnes@sgi.com>
- Joe Korty <joe.korty@ccur.com>
- Matthew Dobson <colpatch@us.ibm.com>
- Rusty Russell <rusty@rustcorp.com.au>
So far as I know, no outstanding issues remain open.

================ Patch Details ================
Here's what each patch does. First are 5 fixup patches
and one minor rework of the cpu_present_map fixup.

pj-fix-1-unifix
pj-fix-2-ashoks-updated-cpuhotplug-6-7
pj-fix-3-ashoks-updated-cpuhotplug-7-7
pj-fix-4-include-mempolicy
pj-fix-5-syscall-return-semicolon
Patches pj-fix-* should match fixes that you (Andrew)
have already picked up. You should ignore these
if what you already have is just as good. They are
here so that I can be precise as to what source I
am using for the basis of the following patches.

nonsmp-cpu-present-map
You (Andrew) worked around a non-SMP build problem
in Ashok's cpuhotplog patches in init/main.c routine
fixup_cpu_present_map().

==> Instead of whatever you did (an ifdef or whatever),
==> Andrew, please take this patch instead.

This patch makes cpu_present_map a real map for all
configurations, instead of a constant for non-SMP.
It also moves the definition of cpu_present_map out of
kernel/cpu.c into kernel/sched.c, because cpu.c isn't
compiled into non-SMP kernels.

==============================================================
The nine main bitmap and cpumask cleanup patches follow.
==============================================================
mask1-bitmap-cleanup-prep
Document the bitmap bit model and handling of unused bits.

Tighten up bitmap so it does not generate nonzero bits
in the unused tail if it is not given any on input.

Add intersects, subset, xor and andnot operators.
Change bitmap_complement to take two operands.

Add a couple of missing 'const' qualifiers on
bitops test_bit and bitmap_equal args.

mask2-bitmap-extensions
This bitmap improvements make it a suitable basis for
fully supporting cpumask_t and nodemask_t. Inline macros
with compile-time checks enable generating tight code on
both small and large systems (large meaning cpumask_t
requires more than one unsigned long's worth of bits).

The existing bitmap_<op> macros in lib/bitmap.c
are renamed to __bitmap_<op>, and wrappers for each
bitmap_<op> are exposed in include/linux/bitmap.h

This patch _includes_ Bill Irwins recent rewrite of the
bitmap_shift operators to not require a fixed length
intermediate bitmap.

Improved comments list each available operator for easy
browsing.

mask3-unline-find-next-bit-ia64
Move the page of code (~700 bytes of instructions)
for find_next_bit and find_next_zero_bit from inline
in include/asm-ia64/bitops.h to a real function in
arch/ia64/lib/bitops.c, leaving a declaration and
macro wrapper behind.

The other arch's with almost this same code might want to
also uninline it: alpha, parisc, ppc, sh, sparc, sparc64.

These are too big to inline.

mask4-new-cpumask-h
Major rewrite of cpumask to use a single implementation,
as a struct-wrapped bitmap.

This patch leaves some 26 include/asm-*/cpumask*.h
header files orphaned - to be removed next patch.

Some nine cpumask macros for const variants and to
coerce and promote between an unsigned long and a
cpumask are obsolete. Simple emulation wrappers are
provided in this patch, which can be removed once each
of the 3 archs (i386, ppc64, x86_64) using them are
recoded in follow-on patches to not need them.

The CPU_MASK_ALL macro now avoids leaving possible
garbage one bits in any unused portion of the high word.

An inproved comment lists all available operators, for
convenient browsing.

mask5-remove-old-cpumask-files
With the cpumask rewrite in the previous patch, these
various include/asm-*/cpumask*.h headers are no longer used.

mask6-cpumask-i386-fixup
Remove by recoding i386 uses of the obsolete cpumask const,
coerce and promote macros.

mask7-cpumask-etc-fixup
Remove by recoding other uses of the obsolete cpumask const,
coerce and promote macros.

mask8-rm-old-cpumask-emul
Now that the emulation of the obsolete cpumask macros is no
longer needed, remove it from cpumask.h

mask9-post-cleanup-tweaks
Make use of for_each_cpu_mask() macro to simplify and optimize
a couple of sparc64 per-CPU loops.

Optimize a bit of cpumask code for asm-i386/mach-es7000

Convert physids_complement() to use both args

Remove cpumask hack from asm-x86_64/topology.h routine
pcibus_to_cpumask().

Clarify and slightly optimize set_cpus_allowed() cpumask check
in kernel/sched.c




--
I won't rest till it's the best ...
Programmer, Linux Scalability
Paul Jackson <pj@sgi.com> 1.650.933.1373
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