[PATCH v6] lib: optimize cpumask_next_and()

From: Clement Courbet
Date: Wed Nov 29 2017 - 04:58:18 EST

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We've measured that we spend ~0.6% of sys cpu time in cpumask_next_and().
It's essentially a joined iteration in search for a non-zero bit, which
is currently implemented as a lookup join (find a nonzero bit on the
lhs, lookup the rhs to see if it's set there).

Implement a direct join (find a nonzero bit on the incrementally built
join).
Also add generic bitmap benchmarks in the new `test_find_bit` module
for new function (see `find_next_and_bit` in [2] and [3] below).

For cpumask_next_and, direct benchmarking shows that it's 1.17x to 14x
faster with a geometric mean of 2.1 on 32 CPUs [1]. No impact on memory
usage.
Note that on Arm, the new pure-C implementation still outperforms
the old one that uses a mix of C and asm (`find_next_bit`) [3].

[1] Approximate benchmark code:

```
unsigned long src1p[nr_cpumask_longs] = {pattern1};
unsigned long src2p[nr_cpumask_longs] = {pattern2};
for (/*a bunch of repetitions*/) {
for (int n = -1; n <= nr_cpu_ids; ++n) {
asm volatile("" : "+rm"(src1p)); // prevent any optimization
asm volatile("" : "+rm"(src2p));
unsigned long result = cpumask_next_and(n, src1p, src2p);
asm volatile("" : "+rm"(result));
}
}
```

Results:
pattern1 pattern2 time_before/time_after
0x0000ffff 0x0000ffff 1.65
0x0000ffff 0x00005555 2.24
0x0000ffff 0x00001111 2.94
0x0000ffff 0x00000000 14.0
0x00005555 0x0000ffff 1.67
0x00005555 0x00005555 1.71
0x00005555 0x00001111 1.90
0x00005555 0x00000000 6.58
0x00001111 0x0000ffff 1.46
0x00001111 0x00005555 1.49
0x00001111 0x00001111 1.45
0x00001111 0x00000000 3.10
0x00000000 0x0000ffff 1.18
0x00000000 0x00005555 1.18
0x00000000 0x00001111 1.17
0x00000000 0x00000000 1.25
-----------------------------
geo.mean 2.06

[2] test_find_next_bit, X86 (skylake)

[ 3913.477422] Start testing find_bit() with random-filled bitmap
[ 3913.477847] find_next_bit: 160868 cycles, 16484 iterations
[ 3913.477933] find_next_zero_bit: 169542 cycles, 16285 iterations
[ 3913.478036] find_last_bit: 201638 cycles, 16483 iterations
[ 3913.480214] find_first_bit: 4353244 cycles, 16484 iterations
[ 3913.480216] Start testing find_next_and_bit() with random-filled
bitmap
[ 3913.481074] find_next_and_bit: 89604 cycles, 8216 iterations
[ 3913.481075] Start testing find_bit() with sparse bitmap
[ 3913.481078] find_next_bit: 2536 cycles, 66 iterations
[ 3913.481252] find_next_zero_bit: 344404 cycles, 32703 iterations
[ 3913.481255] find_last_bit: 2006 cycles, 66 iterations
[ 3913.481265] find_first_bit: 17488 cycles, 66 iterations
[ 3913.481266] Start testing find_next_and_bit() with sparse bitmap
[ 3913.481272] find_next_and_bit: 764 cycles, 1 iterations

[3] test_find_next_bit, arm (v7 odroid XU3).

[ 267.206928] Start testing find_bit() with random-filled bitmap
[ 267.214752] find_next_bit: 4474 cycles, 16419 iterations
[ 267.221850] find_next_zero_bit: 5976 cycles, 16350 iterations
[ 267.229294] find_last_bit: 4209 cycles, 16419 iterations
[ 267.279131] find_first_bit: 1032991 cycles, 16420 iterations
[ 267.286265] Start testing find_next_and_bit() with random-filled
bitmap
[ 267.302386] find_next_and_bit: 2290 cycles, 8140 iterations
[ 267.309422] Start testing find_bit() with sparse bitmap
[ 267.316054] find_next_bit: 191 cycles, 66 iterations
[ 267.322726] find_next_zero_bit: 8758 cycles, 32703 iterations
[ 267.329803] find_last_bit: 84 cycles, 66 iterations
[ 267.336169] find_first_bit: 4118 cycles, 66 iterations
[ 267.342627] Start testing find_next_and_bit() with sparse bitmap
[ 267.356919] find_next_and_bit: 91 cycles, 1 iterations

Signed-off-by: Clement Courbet <courbet@xxxxxxxxxx>
---
Changes in v2:
- Refactored _find_next_common_bit into _find_next_bit., as suggested
by Yury Norov. This has no adverse effects on the performance side,
as the compiler successfully inlines the code.

Changes in v3:
- Fixes find_next_and_bit() declaration.
- Synchronize _find_next_bit_le() with _find_next_bit()
- Synchronize the code in tools/lib/find_bit.c
- Add find_next_and_bit to guard code
- Fix invert value (bad sync with our internal tree on which I'm doing
the testing).

Changes in v4:
- Mark _find_next_bit() inline.

Changes in v5:
- Added benchmarks to test_find_bit.cc
- Fixed arm compilation: added missing header to arm bitops.h

Changes in v6:
- Removed test for reference implementation, which was a temporary
artifact.
- Prettify test output.

arch/arm/include/asm/bitops.h | 1 +
arch/unicore32/include/asm/bitops.h | 2 ++
include/asm-generic/bitops/find.h | 20 +++++++++++
include/linux/bitmap.h | 6 +++-
lib/cpumask.c | 9 ++---
lib/find_bit.c | 59 ++++++++++++++++++++++++---------
lib/test_find_bit.c | 25 +++++++++++++-
tools/include/asm-generic/bitops/find.h | 16 +++++++++
tools/lib/find_bit.c | 40 ++++++++++++++++------
9 files changed, 146 insertions(+), 32 deletions(-)

diff --git a/arch/arm/include/asm/bitops.h b/arch/arm/include/asm/bitops.h
index ce5ee762ed66..4cab9bb823fb 100644
--- a/arch/arm/include/asm/bitops.h
+++ b/arch/arm/include/asm/bitops.h
@@ -338,6 +338,7 @@ static inline int find_next_bit_le(const void *p, int size, int offset)

#endif

+#include <asm-generic/bitops/find.h>
#include <asm-generic/bitops/le.h>

/*
diff --git a/arch/unicore32/include/asm/bitops.h b/arch/unicore32/include/asm/bitops.h
index 401f597bc38c..c0cbdbe17168 100644
--- a/arch/unicore32/include/asm/bitops.h
+++ b/arch/unicore32/include/asm/bitops.h
@@ -44,4 +44,6 @@ static inline int fls(int x)
#define find_first_bit find_first_bit
#define find_first_zero_bit find_first_zero_bit

+#include <asm-generic/bitops/find.h>
+
#endif /* __UNICORE_BITOPS_H__ */
diff --git a/include/asm-generic/bitops/find.h b/include/asm-generic/bitops/find.h
index 1ba611e16fa0..8a1ee10014de 100644
--- a/include/asm-generic/bitops/find.h
+++ b/include/asm-generic/bitops/find.h
@@ -16,6 +16,22 @@ extern unsigned long find_next_bit(const unsigned long *addr, unsigned long
size, unsigned long offset);
#endif

+#ifndef find_next_and_bit
+/**
+ * find_next_and_bit - find the next set bit in both memory regions
+ * @addr1: The first address to base the search on
+ * @addr2: The second address to base the search on
+ * @offset: The bitnumber to start searching at
+ * @size: The bitmap size in bits
+ *
+ * Returns the bit number for the next set bit
+ * If no bits are set, returns @size.
+ */
+extern unsigned long find_next_and_bit(const unsigned long *addr1,
+ const unsigned long *addr2, unsigned long size,
+ unsigned long offset);
+#endif
+
#ifndef find_next_zero_bit
/**
* find_next_zero_bit - find the next cleared bit in a memory region
@@ -55,8 +71,12 @@ extern unsigned long find_first_zero_bit(const unsigned long *addr,
unsigned long size);
#else /* CONFIG_GENERIC_FIND_FIRST_BIT */

+#ifndef find_first_bit
#define find_first_bit(addr, size) find_next_bit((addr), (size), 0)
+#endif
+#ifndef find_first_zero_bit
#define find_first_zero_bit(addr, size) find_next_zero_bit((addr), (size), 0)
+#endif

#endif /* CONFIG_GENERIC_FIND_FIRST_BIT */

diff --git a/include/linux/bitmap.h b/include/linux/bitmap.h
index 3489253e38fc..371408bdb3a6 100644
--- a/include/linux/bitmap.h
+++ b/include/linux/bitmap.h
@@ -83,8 +83,12 @@
* test_and_change_bit(bit, addr) Change bit and return old value
* find_first_zero_bit(addr, nbits) Position first zero bit in *addr
* find_first_bit(addr, nbits) Position first set bit in *addr
- * find_next_zero_bit(addr, nbits, bit) Position next zero bit in *addr >= bit
+ * find_next_zero_bit(addr, nbits, bit)
+ * Position next zero bit in *addr >= bit
* find_next_bit(addr, nbits, bit) Position next set bit in *addr >= bit
+ * find_next_and_bit(addr1, addr2, nbits, bit)
+ * Same as find_next_bit, but in
+ * (*addr1 & *addr2)
*
*/

diff --git a/lib/cpumask.c b/lib/cpumask.c
index 35fe142ebb5e..beca6244671a 100644
--- a/lib/cpumask.c
+++ b/lib/cpumask.c
@@ -33,10 +33,11 @@ EXPORT_SYMBOL(cpumask_next);
int cpumask_next_and(int n, const struct cpumask *src1p,
const struct cpumask *src2p)
{
- while ((n = cpumask_next(n, src1p)) < nr_cpu_ids)
- if (cpumask_test_cpu(n, src2p))
- break;
- return n;
+ /* -1 is a legal arg here. */
+ if (n != -1)
+ cpumask_check(n);
+ return find_next_and_bit(cpumask_bits(src1p), cpumask_bits(src2p),
+ nr_cpumask_bits, n + 1);
}
EXPORT_SYMBOL(cpumask_next_and);

diff --git a/lib/find_bit.c b/lib/find_bit.c
index 6ed74f78380c..ee3df93ba69a 100644
--- a/lib/find_bit.c
+++ b/lib/find_bit.c
@@ -21,22 +21,29 @@
#include <linux/export.h>
#include <linux/kernel.h>

-#if !defined(find_next_bit) || !defined(find_next_zero_bit)
+#if !defined(find_next_bit) || !defined(find_next_zero_bit) || \
+ !defined(find_next_and_bit)

/*
- * This is a common helper function for find_next_bit and
- * find_next_zero_bit. The difference is the "invert" argument, which
- * is XORed with each fetched word before searching it for one bits.
+ * This is a common helper function for find_next_bit, find_next_zero_bit, and
+ * find_next_and_bit. The differences are:
+ * - The "invert" argument, which is XORed with each fetched word before
+ * searching it for one bits.
+ * - The optional "addr2", which is anded with "addr1" if present.
*/
-static unsigned long _find_next_bit(const unsigned long *addr,
- unsigned long nbits, unsigned long start, unsigned long invert)
+static inline unsigned long _find_next_bit(const unsigned long *addr1,
+ const unsigned long *addr2, unsigned long nbits,
+ unsigned long start, unsigned long invert)
{
unsigned long tmp;

if (unlikely(start >= nbits))
return nbits;

- tmp = addr[start / BITS_PER_LONG] ^ invert;
+ tmp = addr1[start / BITS_PER_LONG];
+ if (addr2)
+ tmp &= addr2[start / BITS_PER_LONG];
+ tmp ^= invert;

/* Handle 1st word. */
tmp &= BITMAP_FIRST_WORD_MASK(start);
@@ -47,7 +54,10 @@ static unsigned long _find_next_bit(const unsigned long *addr,
if (start >= nbits)
return nbits;

- tmp = addr[start / BITS_PER_LONG] ^ invert;
+ tmp = addr1[start / BITS_PER_LONG];
+ if (addr2)
+ tmp &= addr2[start / BITS_PER_LONG];
+ tmp ^= invert;
}

return min(start + __ffs(tmp), nbits);
@@ -61,7 +71,7 @@ static unsigned long _find_next_bit(const unsigned long *addr,
unsigned long find_next_bit(const unsigned long *addr, unsigned long size,
unsigned long offset)
{
- return _find_next_bit(addr, size, offset, 0UL);
+ return _find_next_bit(addr, NULL, size, offset, 0UL);
}
EXPORT_SYMBOL(find_next_bit);
#endif
@@ -70,11 +80,21 @@ EXPORT_SYMBOL(find_next_bit);
unsigned long find_next_zero_bit(const unsigned long *addr, unsigned long size,
unsigned long offset)
{
- return _find_next_bit(addr, size, offset, ~0UL);
+ return _find_next_bit(addr, NULL, size, offset, ~0UL);
}
EXPORT_SYMBOL(find_next_zero_bit);
#endif

+#if !defined(find_next_and_bit)
+unsigned long find_next_and_bit(const unsigned long *addr1,
+ const unsigned long *addr2, unsigned long size,
+ unsigned long offset)
+{
+ return _find_next_bit(addr1, addr2, size, offset, 0UL);
+}
+EXPORT_SYMBOL(find_next_and_bit);
+#endif
+
#ifndef find_first_bit
/*
* Find the first set bit in a memory region.
@@ -146,15 +166,19 @@ static inline unsigned long ext2_swab(const unsigned long y)
}

#if !defined(find_next_bit_le) || !defined(find_next_zero_bit_le)
-static unsigned long _find_next_bit_le(const unsigned long *addr,
- unsigned long nbits, unsigned long start, unsigned long invert)
+static inline unsigned long _find_next_bit_le(const unsigned long *addr1,
+ const unsigned long *addr2, unsigned long nbits,
+ unsigned long start, unsigned long invert)
{
unsigned long tmp;

if (unlikely(start >= nbits))
return nbits;

- tmp = addr[start / BITS_PER_LONG] ^ invert;
+ tmp = addr1[start / BITS_PER_LONG];
+ if (addr2)
+ tmp &= addr2[start / BITS_PER_LONG];
+ tmp ^= invert;

/* Handle 1st word. */
tmp &= ext2_swab(BITMAP_FIRST_WORD_MASK(start));
@@ -165,7 +189,10 @@ static unsigned long _find_next_bit_le(const unsigned long *addr,
if (start >= nbits)
return nbits;

- tmp = addr[start / BITS_PER_LONG] ^ invert;
+ tmp = addr1[start / BITS_PER_LONG];
+ if (addr2)
+ tmp &= addr2[start / BITS_PER_LONG];
+ tmp ^= invert;
}

return min(start + __ffs(ext2_swab(tmp)), nbits);
@@ -176,7 +203,7 @@ static unsigned long _find_next_bit_le(const unsigned long *addr,
unsigned long find_next_zero_bit_le(const void *addr, unsigned
long size, unsigned long offset)
{
- return _find_next_bit_le(addr, size, offset, ~0UL);
+ return _find_next_bit_le(addr, NULL, size, offset, ~0UL);
}
EXPORT_SYMBOL(find_next_zero_bit_le);
#endif
@@ -185,7 +212,7 @@ EXPORT_SYMBOL(find_next_zero_bit_le);
unsigned long find_next_bit_le(const void *addr, unsigned
long size, unsigned long offset)
{
- return _find_next_bit_le(addr, size, offset, 0UL);
+ return _find_next_bit_le(addr, NULL, size, offset, 0UL);
}
EXPORT_SYMBOL(find_next_bit_le);
#endif
diff --git a/lib/test_find_bit.c b/lib/test_find_bit.c
index f4394a36f9aa..da024e40c201 100644
--- a/lib/test_find_bit.c
+++ b/lib/test_find_bit.c
@@ -35,6 +35,7 @@
#define SPARSE 500

static DECLARE_BITMAP(bitmap, BITMAP_LEN) __initdata;
+static DECLARE_BITMAP(bitmap2, BITMAP_LEN) __initdata;

/*
* This is Schlemiel the Painter's algorithm. It should be called after
@@ -107,6 +108,22 @@ static int __init test_find_last_bit(const void *bitmap, unsigned long len)
return 0;
}

+static int __init test_find_next_and_bit(const void *bitmap,
+ const void *bitmap2, unsigned long len)
+{
+ unsigned long i, cnt;
+ cycles_t cycles;
+
+ cycles = get_cycles();
+ for (cnt = i = 0; i < BITMAP_LEN; cnt++)
+ i = find_next_and_bit(bitmap, bitmap2, BITMAP_LEN, i+1);
+ cycles = get_cycles() - cycles;
+ pr_err("find_next_and_bit:\t\t%llu cycles, %ld iterations\n",
+ (u64)cycles, cnt);
+
+ return 0;
+}
+
static int __init find_bit_test(void)
{
unsigned long nbits = BITMAP_LEN / SPARSE;
@@ -114,23 +131,29 @@ static int __init find_bit_test(void)
pr_err("\nStart testing find_bit() with random-filled bitmap\n");

get_random_bytes(bitmap, sizeof(bitmap));
+ get_random_bytes(bitmap2, sizeof(bitmap2));

test_find_next_bit(bitmap, BITMAP_LEN);
test_find_next_zero_bit(bitmap, BITMAP_LEN);
test_find_last_bit(bitmap, BITMAP_LEN);
test_find_first_bit(bitmap, BITMAP_LEN);
+ test_find_next_and_bit(bitmap, bitmap2, BITMAP_LEN);

pr_err("\nStart testing find_bit() with sparse bitmap\n");

bitmap_zero(bitmap, BITMAP_LEN);
+ bitmap_zero(bitmap2, BITMAP_LEN);

- while (nbits--)
+ while (nbits--) {
__set_bit(prandom_u32() % BITMAP_LEN, bitmap);
+ __set_bit(prandom_u32() % BITMAP_LEN, bitmap2);
+ }

test_find_next_bit(bitmap, BITMAP_LEN);
test_find_next_zero_bit(bitmap, BITMAP_LEN);
test_find_last_bit(bitmap, BITMAP_LEN);
test_find_first_bit(bitmap, BITMAP_LEN);
+ test_find_next_and_bit(bitmap, bitmap2, BITMAP_LEN);

return 0;
}
diff --git a/tools/include/asm-generic/bitops/find.h b/tools/include/asm-generic/bitops/find.h
index 9311fadaaab2..16ed1982cb34 100644
--- a/tools/include/asm-generic/bitops/find.h
+++ b/tools/include/asm-generic/bitops/find.h
@@ -16,6 +16,22 @@ extern unsigned long find_next_bit(const unsigned long *addr, unsigned long
size, unsigned long offset);
#endif

+#ifndef find_next_and_bit
+/**
+ * find_next_and_bit - find the next set bit in both memory regions
+ * @addr1: The first address to base the search on
+ * @addr2: The second address to base the search on
+ * @offset: The bitnumber to start searching at
+ * @size: The bitmap size in bits
+ *
+ * Returns the bit number for the next set bit
+ * If no bits are set, returns @size.
+ */
+extern unsigned long find_next_and_bit(const unsigned long *addr1,
+ const unsigned long *addr2, unsigned long size,
+ unsigned long offset);
+#endif
+
#ifndef find_next_zero_bit

/**
diff --git a/tools/lib/find_bit.c b/tools/lib/find_bit.c
index 42c15f906aac..9474f5856d4e 100644
--- a/tools/lib/find_bit.c
+++ b/tools/lib/find_bit.c
@@ -22,22 +22,29 @@
#include <linux/bitmap.h>
#include <linux/kernel.h>

-#if !defined(find_next_bit)
+#if !defined(find_next_bit) || !defined(find_next_zero_bit) || \
+ !defined(find_next_and_bit)

/*
- * This is a common helper function for find_next_bit and
- * find_next_zero_bit. The difference is the "invert" argument, which
- * is XORed with each fetched word before searching it for one bits.
+ * This is a common helper function for find_next_bit, find_next_zero_bit, and
+ * find_next_and_bit. The differences are:
+ * - The "invert" argument, which is XORed with each fetched word before
+ * searching it for one bits.
+ * - The optional "addr2", which is anded with "addr1" if present.
*/
-static unsigned long _find_next_bit(const unsigned long *addr,
- unsigned long nbits, unsigned long start, unsigned long invert)
+static inline unsigned long _find_next_bit(const unsigned long *addr1,
+ const unsigned long *addr2, unsigned long nbits,
+ unsigned long start, unsigned long invert)
{
unsigned long tmp;

if (unlikely(start >= nbits))
return nbits;

- tmp = addr[start / BITS_PER_LONG] ^ invert;
+ tmp = addr1[start / BITS_PER_LONG];
+ if (addr2)
+ tmp &= addr2[start / BITS_PER_LONG];
+ tmp ^= invert;

/* Handle 1st word. */
tmp &= BITMAP_FIRST_WORD_MASK(start);
@@ -48,7 +55,10 @@ static unsigned long _find_next_bit(const unsigned long *addr,
if (start >= nbits)
return nbits;

- tmp = addr[start / BITS_PER_LONG] ^ invert;
+ tmp = addr1[start / BITS_PER_LONG];
+ if (addr2)
+ tmp &= addr2[start / BITS_PER_LONG];
+ tmp ^= invert;
}

return min(start + __ffs(tmp), nbits);
@@ -62,7 +72,7 @@ static unsigned long _find_next_bit(const unsigned long *addr,
unsigned long find_next_bit(const unsigned long *addr, unsigned long size,
unsigned long offset)
{
- return _find_next_bit(addr, size, offset, 0UL);
+ return _find_next_bit(addr, NULL, size, offset, 0UL);
}
#endif

@@ -104,6 +114,16 @@ unsigned long find_first_zero_bit(const unsigned long *addr, unsigned long size)
unsigned long find_next_zero_bit(const unsigned long *addr, unsigned long size,
unsigned long offset)
{
- return _find_next_bit(addr, size, offset, ~0UL);
+ return _find_next_bit(addr, NULL, size, offset, ~0UL);
}
#endif
+
+#ifndef find_next_and_bit
+unsigned long find_next_and_bit(const unsigned long *addr1,
+ const unsigned long *addr2, unsigned long size,
+ unsigned long offset)
+{
+ return _find_next_bit(addr1, addr2, size, offset, 0UL);
+}
+#endif
+
--
2.15.0.417.g466bffb3ac-goog

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