mirror of
https://mirrors.bfsu.edu.cn/git/linux.git
synced 2024-12-16 23:45:31 +08:00
a0019cd7d4
Adding support to have priv pointer in swap callback function.
Following the initial change on cmp callback functions [1]
and adding SWAP_WRAPPER macro to identify sort call of sort_r.
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org>
Link: https://lore.kernel.org/bpf/20220316122419.933957-2-jolsa@kernel.org
[1] 4333fb96ca
("media: lib/sort.c: implement sort() variant taking context argument")
293 lines
8.9 KiB
C
293 lines
8.9 KiB
C
// SPDX-License-Identifier: GPL-2.0
|
|
/*
|
|
* A fast, small, non-recursive O(n log n) sort for the Linux kernel
|
|
*
|
|
* This performs n*log2(n) + 0.37*n + o(n) comparisons on average,
|
|
* and 1.5*n*log2(n) + O(n) in the (very contrived) worst case.
|
|
*
|
|
* Glibc qsort() manages n*log2(n) - 1.26*n for random inputs (1.63*n
|
|
* better) at the expense of stack usage and much larger code to avoid
|
|
* quicksort's O(n^2) worst case.
|
|
*/
|
|
|
|
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
|
|
|
|
#include <linux/types.h>
|
|
#include <linux/export.h>
|
|
#include <linux/sort.h>
|
|
|
|
/**
|
|
* is_aligned - is this pointer & size okay for word-wide copying?
|
|
* @base: pointer to data
|
|
* @size: size of each element
|
|
* @align: required alignment (typically 4 or 8)
|
|
*
|
|
* Returns true if elements can be copied using word loads and stores.
|
|
* The size must be a multiple of the alignment, and the base address must
|
|
* be if we do not have CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS.
|
|
*
|
|
* For some reason, gcc doesn't know to optimize "if (a & mask || b & mask)"
|
|
* to "if ((a | b) & mask)", so we do that by hand.
|
|
*/
|
|
__attribute_const__ __always_inline
|
|
static bool is_aligned(const void *base, size_t size, unsigned char align)
|
|
{
|
|
unsigned char lsbits = (unsigned char)size;
|
|
|
|
(void)base;
|
|
#ifndef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
|
|
lsbits |= (unsigned char)(uintptr_t)base;
|
|
#endif
|
|
return (lsbits & (align - 1)) == 0;
|
|
}
|
|
|
|
/**
|
|
* swap_words_32 - swap two elements in 32-bit chunks
|
|
* @a: pointer to the first element to swap
|
|
* @b: pointer to the second element to swap
|
|
* @n: element size (must be a multiple of 4)
|
|
*
|
|
* Exchange the two objects in memory. This exploits base+index addressing,
|
|
* which basically all CPUs have, to minimize loop overhead computations.
|
|
*
|
|
* For some reason, on x86 gcc 7.3.0 adds a redundant test of n at the
|
|
* bottom of the loop, even though the zero flag is still valid from the
|
|
* subtract (since the intervening mov instructions don't alter the flags).
|
|
* Gcc 8.1.0 doesn't have that problem.
|
|
*/
|
|
static void swap_words_32(void *a, void *b, size_t n)
|
|
{
|
|
do {
|
|
u32 t = *(u32 *)(a + (n -= 4));
|
|
*(u32 *)(a + n) = *(u32 *)(b + n);
|
|
*(u32 *)(b + n) = t;
|
|
} while (n);
|
|
}
|
|
|
|
/**
|
|
* swap_words_64 - swap two elements in 64-bit chunks
|
|
* @a: pointer to the first element to swap
|
|
* @b: pointer to the second element to swap
|
|
* @n: element size (must be a multiple of 8)
|
|
*
|
|
* Exchange the two objects in memory. This exploits base+index
|
|
* addressing, which basically all CPUs have, to minimize loop overhead
|
|
* computations.
|
|
*
|
|
* We'd like to use 64-bit loads if possible. If they're not, emulating
|
|
* one requires base+index+4 addressing which x86 has but most other
|
|
* processors do not. If CONFIG_64BIT, we definitely have 64-bit loads,
|
|
* but it's possible to have 64-bit loads without 64-bit pointers (e.g.
|
|
* x32 ABI). Are there any cases the kernel needs to worry about?
|
|
*/
|
|
static void swap_words_64(void *a, void *b, size_t n)
|
|
{
|
|
do {
|
|
#ifdef CONFIG_64BIT
|
|
u64 t = *(u64 *)(a + (n -= 8));
|
|
*(u64 *)(a + n) = *(u64 *)(b + n);
|
|
*(u64 *)(b + n) = t;
|
|
#else
|
|
/* Use two 32-bit transfers to avoid base+index+4 addressing */
|
|
u32 t = *(u32 *)(a + (n -= 4));
|
|
*(u32 *)(a + n) = *(u32 *)(b + n);
|
|
*(u32 *)(b + n) = t;
|
|
|
|
t = *(u32 *)(a + (n -= 4));
|
|
*(u32 *)(a + n) = *(u32 *)(b + n);
|
|
*(u32 *)(b + n) = t;
|
|
#endif
|
|
} while (n);
|
|
}
|
|
|
|
/**
|
|
* swap_bytes - swap two elements a byte at a time
|
|
* @a: pointer to the first element to swap
|
|
* @b: pointer to the second element to swap
|
|
* @n: element size
|
|
*
|
|
* This is the fallback if alignment doesn't allow using larger chunks.
|
|
*/
|
|
static void swap_bytes(void *a, void *b, size_t n)
|
|
{
|
|
do {
|
|
char t = ((char *)a)[--n];
|
|
((char *)a)[n] = ((char *)b)[n];
|
|
((char *)b)[n] = t;
|
|
} while (n);
|
|
}
|
|
|
|
/*
|
|
* The values are arbitrary as long as they can't be confused with
|
|
* a pointer, but small integers make for the smallest compare
|
|
* instructions.
|
|
*/
|
|
#define SWAP_WORDS_64 (swap_r_func_t)0
|
|
#define SWAP_WORDS_32 (swap_r_func_t)1
|
|
#define SWAP_BYTES (swap_r_func_t)2
|
|
#define SWAP_WRAPPER (swap_r_func_t)3
|
|
|
|
struct wrapper {
|
|
cmp_func_t cmp;
|
|
swap_func_t swap;
|
|
};
|
|
|
|
/*
|
|
* The function pointer is last to make tail calls most efficient if the
|
|
* compiler decides not to inline this function.
|
|
*/
|
|
static void do_swap(void *a, void *b, size_t size, swap_r_func_t swap_func, const void *priv)
|
|
{
|
|
if (swap_func == SWAP_WRAPPER) {
|
|
((const struct wrapper *)priv)->swap(a, b, (int)size);
|
|
return;
|
|
}
|
|
|
|
if (swap_func == SWAP_WORDS_64)
|
|
swap_words_64(a, b, size);
|
|
else if (swap_func == SWAP_WORDS_32)
|
|
swap_words_32(a, b, size);
|
|
else if (swap_func == SWAP_BYTES)
|
|
swap_bytes(a, b, size);
|
|
else
|
|
swap_func(a, b, (int)size, priv);
|
|
}
|
|
|
|
#define _CMP_WRAPPER ((cmp_r_func_t)0L)
|
|
|
|
static int do_cmp(const void *a, const void *b, cmp_r_func_t cmp, const void *priv)
|
|
{
|
|
if (cmp == _CMP_WRAPPER)
|
|
return ((const struct wrapper *)priv)->cmp(a, b);
|
|
return cmp(a, b, priv);
|
|
}
|
|
|
|
/**
|
|
* parent - given the offset of the child, find the offset of the parent.
|
|
* @i: the offset of the heap element whose parent is sought. Non-zero.
|
|
* @lsbit: a precomputed 1-bit mask, equal to "size & -size"
|
|
* @size: size of each element
|
|
*
|
|
* In terms of array indexes, the parent of element j = @i/@size is simply
|
|
* (j-1)/2. But when working in byte offsets, we can't use implicit
|
|
* truncation of integer divides.
|
|
*
|
|
* Fortunately, we only need one bit of the quotient, not the full divide.
|
|
* @size has a least significant bit. That bit will be clear if @i is
|
|
* an even multiple of @size, and set if it's an odd multiple.
|
|
*
|
|
* Logically, we're doing "if (i & lsbit) i -= size;", but since the
|
|
* branch is unpredictable, it's done with a bit of clever branch-free
|
|
* code instead.
|
|
*/
|
|
__attribute_const__ __always_inline
|
|
static size_t parent(size_t i, unsigned int lsbit, size_t size)
|
|
{
|
|
i -= size;
|
|
i -= size & -(i & lsbit);
|
|
return i / 2;
|
|
}
|
|
|
|
/**
|
|
* sort_r - sort an array of elements
|
|
* @base: pointer to data to sort
|
|
* @num: number of elements
|
|
* @size: size of each element
|
|
* @cmp_func: pointer to comparison function
|
|
* @swap_func: pointer to swap function or NULL
|
|
* @priv: third argument passed to comparison function
|
|
*
|
|
* This function does a heapsort on the given array. You may provide
|
|
* a swap_func function if you need to do something more than a memory
|
|
* copy (e.g. fix up pointers or auxiliary data), but the built-in swap
|
|
* avoids a slow retpoline and so is significantly faster.
|
|
*
|
|
* Sorting time is O(n log n) both on average and worst-case. While
|
|
* quicksort is slightly faster on average, it suffers from exploitable
|
|
* O(n*n) worst-case behavior and extra memory requirements that make
|
|
* it less suitable for kernel use.
|
|
*/
|
|
void sort_r(void *base, size_t num, size_t size,
|
|
cmp_r_func_t cmp_func,
|
|
swap_r_func_t swap_func,
|
|
const void *priv)
|
|
{
|
|
/* pre-scale counters for performance */
|
|
size_t n = num * size, a = (num/2) * size;
|
|
const unsigned int lsbit = size & -size; /* Used to find parent */
|
|
|
|
if (!a) /* num < 2 || size == 0 */
|
|
return;
|
|
|
|
/* called from 'sort' without swap function, let's pick the default */
|
|
if (swap_func == SWAP_WRAPPER && !((struct wrapper *)priv)->swap)
|
|
swap_func = NULL;
|
|
|
|
if (!swap_func) {
|
|
if (is_aligned(base, size, 8))
|
|
swap_func = SWAP_WORDS_64;
|
|
else if (is_aligned(base, size, 4))
|
|
swap_func = SWAP_WORDS_32;
|
|
else
|
|
swap_func = SWAP_BYTES;
|
|
}
|
|
|
|
/*
|
|
* Loop invariants:
|
|
* 1. elements [a,n) satisfy the heap property (compare greater than
|
|
* all of their children),
|
|
* 2. elements [n,num*size) are sorted, and
|
|
* 3. a <= b <= c <= d <= n (whenever they are valid).
|
|
*/
|
|
for (;;) {
|
|
size_t b, c, d;
|
|
|
|
if (a) /* Building heap: sift down --a */
|
|
a -= size;
|
|
else if (n -= size) /* Sorting: Extract root to --n */
|
|
do_swap(base, base + n, size, swap_func, priv);
|
|
else /* Sort complete */
|
|
break;
|
|
|
|
/*
|
|
* Sift element at "a" down into heap. This is the
|
|
* "bottom-up" variant, which significantly reduces
|
|
* calls to cmp_func(): we find the sift-down path all
|
|
* the way to the leaves (one compare per level), then
|
|
* backtrack to find where to insert the target element.
|
|
*
|
|
* Because elements tend to sift down close to the leaves,
|
|
* this uses fewer compares than doing two per level
|
|
* on the way down. (A bit more than half as many on
|
|
* average, 3/4 worst-case.)
|
|
*/
|
|
for (b = a; c = 2*b + size, (d = c + size) < n;)
|
|
b = do_cmp(base + c, base + d, cmp_func, priv) >= 0 ? c : d;
|
|
if (d == n) /* Special case last leaf with no sibling */
|
|
b = c;
|
|
|
|
/* Now backtrack from "b" to the correct location for "a" */
|
|
while (b != a && do_cmp(base + a, base + b, cmp_func, priv) >= 0)
|
|
b = parent(b, lsbit, size);
|
|
c = b; /* Where "a" belongs */
|
|
while (b != a) { /* Shift it into place */
|
|
b = parent(b, lsbit, size);
|
|
do_swap(base + b, base + c, size, swap_func, priv);
|
|
}
|
|
}
|
|
}
|
|
EXPORT_SYMBOL(sort_r);
|
|
|
|
void sort(void *base, size_t num, size_t size,
|
|
cmp_func_t cmp_func,
|
|
swap_func_t swap_func)
|
|
{
|
|
struct wrapper w = {
|
|
.cmp = cmp_func,
|
|
.swap = swap_func,
|
|
};
|
|
|
|
return sort_r(base, num, size, _CMP_WRAPPER, SWAP_WRAPPER, &w);
|
|
}
|
|
EXPORT_SYMBOL(sort);
|