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In the following patches the function is used to implement in-place bitmaps
traversing without storing intermediate result in temporary bitmaps.
Signed-off-by: Yury Norov <yury.norov@gmail.com>
Acked-by: Tariq Toukan <tariqt@nvidia.com>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Reviewed-by: Peter Lafreniere <peter@n8pjl.ca>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
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for_each_cpu_and() is very convenient as it saves having to allocate a
temporary cpumask to store the result of cpumask_and(). The same issue
applies to cpumask_andnot() which doesn't actually need temporary storage
for iteration purposes.
Following what has been done for for_each_cpu_and(), introduce
for_each_cpu_andnot().
Signed-off-by: Valentin Schneider <vschneid@redhat.com>
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In preparation of introducing for_each_cpu_andnot(), add a variant of
find_next_bit() that negate the bits in @addr2 when ANDing them with the
bits in @addr1.
Signed-off-by: Valentin Schneider <vschneid@redhat.com>
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Moving an iterator of the macros inside conditional part of for-loop
helps to generate a better code. It had been first implemented in commit
7baac8b91f9871ba ("cpumask: make for_each_cpu_mask a bit smaller").
Now that cpumask for-loops are the aliases to bitmap loops, it's worth
to optimize them the same way.
Bloat-o-meter says:
add/remove: 8/12 grow/shrink: 147/592 up/down: 4876/-24416 (-19540)
Signed-off-by: Yury Norov <yury.norov@gmail.com>
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Add for_each_set_bit_wrap() macro and use it in for_each_cpu_wrap(). The
new macro is based on __for_each_wrap() iterator, which is simpler and
smaller than cpumask_next_wrap().
Signed-off-by: Yury Norov <yury.norov@gmail.com>
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The helper is better optimized for the worst case: in case of empty
cpumask, current code traverses 2 * size:
next = cpumask_next_and(prev, src1p, src2p);
if (next >= nr_cpu_ids)
next = cpumask_first_and(src1p, src2p);
At bitmap level we can stop earlier after checking 'size + offset' bits.
Signed-off-by: Yury Norov <yury.norov@gmail.com>
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The difference between for_each_cpu() and for_each_set_bit()
is that the latter uses cpumask_next() instead of find_next_bit(),
and so calls cpumask_check().
This check is useless because the iterator value is not provided by
user. It generates false-positives for the very last iteration
of for_each_cpu().
Signed-off-by: Yury Norov <yury.norov@gmail.com>
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Kernel lacks for a function that searches for Nth bit in a bitmap.
Usually people do it like this:
for_each_set_bit(bit, mask, size)
if (n-- == 0)
return bit;
We can do it more efficiently, if we:
1. find a word containing Nth bit, using hweight(); and
2. find the bit, using a helper fns(), that works similarly to
__ffs() and ffz().
fns() is implemented as a simple loop. For x86_64, there's PDEP instruction
to do that: ret = clz(pdep(1 << idx, num)). However, for large bitmaps the
most of improvement comes from using hweight(), so I kept fns() simple.
New find_nth_bit() is ~70 times faster on x86_64/kvm in find_bit benchmark:
find_nth_bit: 7154190 ns, 16411 iterations
for_each_bit: 505493126 ns, 16315 iterations
With all that, a family of 3 new functions is added, and used where
appropriate in the following patches.
Signed-off-by: Yury Norov <yury.norov@gmail.com>
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Over the past couple years, the function _find_next_bit() was extended
with parameters that modify its behavior to implement and- zero- and le-
flavors. The parameters are passed at compile time, but current design
prevents a compiler from optimizing out the conditionals.
As find_next_bit() API grows, I expect that more parameters will be added.
Current design would require more conditional code in _find_next_bit(),
which would bloat the helper even more and make it barely readable.
This patch replaces _find_next_bit() with a macro FIND_NEXT_BIT, and adds
a set of wrappers, so that the compile-time optimizations become possible.
The common logic is moved to the new macro, and all flavors may be
generated by providing a FETCH macro parameter, like in this example:
#define FIND_NEXT_BIT(FETCH, MUNGE, size, start) ...
find_next_xornot_and_bit(addr1, addr2, addr3, size, start)
{
return FIND_NEXT_BIT(addr1[idx] ^ ~addr2[idx] & addr3[idx],
/* nop */, size, start);
}
The FETCH may be of any complexity, as soon as it only refers the bitmap(s)
and an iterator idx.
MUNGE is here to support _le code generation for BE builds. May be
empty.
I ran find_bit_benchmark 16 times on top of 6.0-rc2 and 16 times on top
of 6.0-rc2 + this series. The results for kvm/x86_64 are:
v6.0-rc2 Optimized Difference Z-score
Random dense bitmap ns ns ns %
find_next_bit: 787735 670546 117189 14.9 3.97
find_next_zero_bit: 777492 664208 113284 14.6 10.51
find_last_bit: 830925 687573 143352 17.3 2.35
find_first_bit: 3874366 3306635 567731 14.7 1.84
find_first_and_bit: 40677125 37739887 2937238 7.2 1.36
find_next_and_bit: 347865 304456 43409 12.5 1.35
Random sparse bitmap
find_next_bit: 19816 14021 5795 29.2 6.10
find_next_zero_bit: 1318901 1223794 95107 7.2 1.41
find_last_bit: 14573 13514 1059 7.3 6.92
find_first_bit: 1313321 1249024 64297 4.9 1.53
find_first_and_bit: 8921 8098 823 9.2 4.56
find_next_and_bit: 9796 7176 2620 26.7 5.39
Where the statistics is significant (z-score > 3), the improvement
is ~15%.
According to the bloat-o-meter, the Image size is 10-11K less:
x86_64/defconfig:
add/remove: 32/14 grow/shrink: 61/782 up/down: 6344/-16521 (-10177)
arm64/defconfig:
add/remove: 3/2 grow/shrink: 50/714 up/down: 608/-11556 (-10948)
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Yury Norov <yury.norov@gmail.com>
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find_first_zero_bit_le() is an alias to find_next_zero_bit_le(),
despite that 'next' is known to be slower than 'first' version.
Now that we have common FIND_FIRST_BIT() macro helper, it's trivial
to implement find_first_zero_bit_le() as a real function.
Reviewed-by: Valentin Schneider <vschneid@redhat.com>
Signed-off-by: Yury Norov <yury.norov@gmail.com>
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The order of the arguments in function documentation doesn't fit the
implementation. Change the documentation so that it corresponds to the
code. This prevent people to get confused when reading the documentation.
Signed-off-by: Anna-Maria Behnsen <anna-maria@linutronix.de>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Yury Norov <yury.norov@gmail.com>
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bitmap_for_each_{set,clear}_region() are similar to for_each_bit()
macros in include/linux/find.h, but interface and implementation
of them are different.
This patch adds for_each_bitrange() macros and drops unused
bitmap_*_region() API in sake of unification.
Signed-off-by: Yury Norov <yury.norov@gmail.com>
Tested-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Acked-by: Dennis Zhou <dennis@kernel.org>
Acked-by: Ulf Hansson <ulf.hansson@linaro.org> # For MMC
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The macros iterate thru all set/clear bits in a bitmap. They search a
first bit using find_first_bit(), and the rest bits using find_next_bit().
Since find_next_bit() is called shortly after find_first_bit(), we can
save few lines of I-cache by not using find_first_bit().
Signed-off-by: Yury Norov <yury.norov@gmail.com>
Tested-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
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for_each_bit() macros depend on find_bit() machinery, and so the
proper place for them is the find.h header.
Signed-off-by: Yury Norov <yury.norov@gmail.com>
Tested-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
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Currently find_first_and_bit() is an alias to find_next_and_bit(). However,
it is widely used in cpumask, so it worth to optimize it. This patch adds
its own implementation for find_first_and_bit().
On x86_64 find_bit_benchmark says:
Before (#define find_first_and_bit(...) find_next_and_bit(..., 0):
Start testing find_bit() with random-filled bitmap
[ 140.291468] find_first_and_bit: 46890919 ns, 32671 iterations
Start testing find_bit() with sparse bitmap
[ 140.295028] find_first_and_bit: 7103 ns, 1 iterations
After:
Start testing find_bit() with random-filled bitmap
[ 162.574907] find_first_and_bit: 25045813 ns, 32846 iterations
Start testing find_bit() with sparse bitmap
[ 162.578458] find_first_and_bit: 4900 ns, 1 iterations
(Thanks to Alexey Klimov for thorough testing.)
Signed-off-by: Yury Norov <yury.norov@gmail.com>
Tested-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Tested-by: Alexey Klimov <aklimov@redhat.com>
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In 5.12 cycle we enabled GENERIC_FIND_FIRST_BIT config option for ARM64
and MIPS. It increased performance and shrunk .text size; and so far
I didn't receive any negative feedback on the change.
https://lore.kernel.org/linux-arch/20210225135700.1381396-1-yury.norov@gmail.com/
Now I think it's a good time to switch all architectures to use
find_{first,last}_bit() unconditionally, and so remove corresponding
config option.
The patch does't introduce functioal changes for arc, arm, arm64, mips,
m68k, s390 and x86, for other architectures I expect improvement both in
performance and .text size.
Signed-off-by: Yury Norov <yury.norov@gmail.com>
Tested-by: Alexander Lobakin <alobakin@pm.me> (mips)
Reviewed-by: Alexander Lobakin <alobakin@pm.me> (mips)
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Will Deacon <will@kernel.org>
Tested-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
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find_bit API and bitmap API are closely related, but inclusion paths
are different - include/asm-generic and include/linux, correspondingly.
In the past it made a lot of troubles due to circular dependencies
and/or undefined symbols. Fix this by moving find.h under include/linux.
Signed-off-by: Yury Norov <yury.norov@gmail.com>
Tested-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>
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