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cutils: Rearrange buffer_is_zero acceleration 

Allow selection of several acceleration functions
based on the size and alignment of the buffer.
Do not require ifunc support for AVX2 acceleration.

Signed-off-by: Richard Henderson <rth@twiddle.net>
Message-Id: <1472496380-19706-5-git-send-email-rth@twiddle.net>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
master
Richard Henderson 2016-08-29 11:46:15 -07:00 committed by Paolo Bonzini
parent a1febc4950
commit 5e33a87222
2 changed files with 180 additions and 223 deletions
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21
configure vendored
View File

@ -1794,28 +1794,19 @@ fi
##########################################
# avx2 optimization requirement check
if test "$static" = "no" ; then
cat > $TMPC << EOF
cat > $TMPC << EOF
#pragma GCC push_options
#pragma GCC target("avx2")
#include <cpuid.h>
#include <immintrin.h>
static int bar(void *a) {
return _mm256_movemask_epi8(_mm256_cmpeq_epi8(*(__m256i *)a, (__m256i){0}));
__m256i x = *(__m256i *)a;
return _mm256_testz_si256(x, x);
}
static void *bar_ifunc(void) {return (void*) bar;}
int foo(void *a) __attribute__((ifunc("bar_ifunc")));
int main(int argc, char *argv[]) { return foo(argv[0]);}
int main(int argc, char *argv[]) { return bar(argv[0]); }
EOF
if compile_object "" ; then
if has readelf; then
if readelf --syms $TMPO 2>/dev/null |grep -q "IFUNC.*foo"; then
avx2_opt="yes"
fi
fi
fi
if compile_object "" ; then
avx2_opt="yes"
fi
#########################################

382
util/bufferiszero.c
View File

@ -24,245 +24,211 @@
#include "qemu/osdep.h"
#include "qemu-common.h"
#include "qemu/cutils.h"
#include "qemu/bswap.h"
/* vector definitions */
#ifdef __ALTIVEC__
extern void link_error(void);
#define ACCEL_BUFFER_ZERO(NAME, SIZE, VECTYPE, NONZERO) \
static bool NAME(const void *buf, size_t len) \
{ \
const void *end = buf + len; \
do { \
const VECTYPE *p = buf; \
VECTYPE t; \
if (SIZE == sizeof(VECTYPE) * 4) { \
t = (p[0] | p[1]) | (p[2] | p[3]); \
} else if (SIZE == sizeof(VECTYPE) * 8) { \
t = p[0] | p[1]; \
t |= p[2] | p[3]; \
t |= p[4] | p[5]; \
t |= p[6] | p[7]; \
} else { \
link_error(); \
} \
if (unlikely(NONZERO(t))) { \
return false; \
} \
buf += SIZE; \
} while (buf < end); \
return true; \
}
static bool
buffer_zero_int(const void *buf, size_t len)
{
if (unlikely(len < 8)) {
/* For a very small buffer, simply accumulate all the bytes. */
const unsigned char *p = buf;
const unsigned char *e = buf + len;
unsigned char t = 0;
do {
t |= *p++;
} while (p < e);
return t == 0;
} else {
/* Otherwise, use the unaligned memory access functions to
handle the beginning and end of the buffer, with a couple
of loops handling the middle aligned section. */
uint64_t t = ldq_he_p(buf);
const uint64_t *p = (uint64_t *)(((uintptr_t)buf + 8) & -8);
const uint64_t *e = (uint64_t *)(((uintptr_t)buf + len) & -8);
for (; p + 8 <= e; p += 8) {
__builtin_prefetch(p + 8);
if (t) {
return false;
}
t = p[0] | p[1] | p[2] | p[3] | p[4] | p[5] | p[6] | p[7];
}
while (p < e) {
t |= *p++;
}
t |= ldq_he_p(buf + len - 8);
return t == 0;
}
}
#if defined(__ALTIVEC__)
#include <altivec.h>
/* The altivec.h header says we're allowed to undef these for
* C++ compatibility. Here we don't care about C++, but we
* undef them anyway to avoid namespace pollution.
* altivec.h may redefine the bool macro as vector type.
* Reset it to POSIX semantics.
*/
#undef vector
#undef pixel
#undef bool
#define VECTYPE __vector unsigned char
#define ALL_EQ(v1, v2) vec_all_eq(v1, v2)
#define VEC_OR(v1, v2) ((v1) | (v2))
/* altivec.h may redefine the bool macro as vector type.
* Reset it to POSIX semantics. */
#define bool _Bool
#elif defined __SSE2__
#define DO_NONZERO(X) vec_any_ne(X, (__vector unsigned char){ 0 })
ACCEL_BUFFER_ZERO(buffer_zero_ppc, 128, __vector unsigned char, DO_NONZERO)
static bool select_accel_fn(const void *buf, size_t len)
{
uintptr_t ibuf = (uintptr_t)buf;
if (len % 128 == 0 && ibuf % sizeof(__vector unsigned char) == 0) {
return buffer_zero_ppc(buf, len);
}
return buffer_zero_int(buf, len);
}
#elif defined(CONFIG_AVX2_OPT) || (defined(CONFIG_CPUID_H) && defined(__SSE2__))
#include <cpuid.h>
/* Do not use push_options pragmas unnecessarily, because clang
* does not support them.
*/
#ifndef __SSE2__
#pragma GCC push_options
#pragma GCC target("sse2")
#endif
#include <emmintrin.h>
#define VECTYPE __m128i
#define ALL_EQ(v1, v2) (_mm_movemask_epi8(_mm_cmpeq_epi8(v1, v2)) == 0xFFFF)
#define VEC_OR(v1, v2) (_mm_or_si128(v1, v2))
#elif defined(__aarch64__)
#include "arm_neon.h"
#define VECTYPE uint64x2_t
#define ALL_EQ(v1, v2) \
((vgetq_lane_u64(v1, 0) == vgetq_lane_u64(v2, 0)) && \
(vgetq_lane_u64(v1, 1) == vgetq_lane_u64(v2, 1)))
#define VEC_OR(v1, v2) ((v1) | (v2))
#else
#define VECTYPE unsigned long
#define ALL_EQ(v1, v2) ((v1) == (v2))
#define VEC_OR(v1, v2) ((v1) | (v2))
#define SSE2_NONZERO(X) \
(_mm_movemask_epi8(_mm_cmpeq_epi8((X), _mm_setzero_si128())) != 0xFFFF)
ACCEL_BUFFER_ZERO(buffer_zero_sse2, 64, __m128i, SSE2_NONZERO)
#ifndef __SSE2__
#pragma GCC pop_options
#endif
#define BUFFER_FIND_NONZERO_OFFSET_UNROLL_FACTOR 8
static bool
can_use_buffer_find_nonzero_offset_inner(const void *buf, size_t len)
{
return (len % (BUFFER_FIND_NONZERO_OFFSET_UNROLL_FACTOR
* sizeof(VECTYPE)) == 0
&& ((uintptr_t) buf) % sizeof(VECTYPE) == 0);
}
/*
* Searches for an area with non-zero content in a buffer
*
* Attention! The len must be a multiple of
* BUFFER_FIND_NONZERO_OFFSET_UNROLL_FACTOR * sizeof(VECTYPE)
* and addr must be a multiple of sizeof(VECTYPE) due to
* restriction of optimizations in this function.
*
* can_use_buffer_find_nonzero_offset_inner() can be used to
* check these requirements.
*
* The return value is the offset of the non-zero area rounded
* down to a multiple of sizeof(VECTYPE) for the first
* BUFFER_FIND_NONZERO_OFFSET_UNROLL_FACTOR chunks and down to
* BUFFER_FIND_NONZERO_OFFSET_UNROLL_FACTOR * sizeof(VECTYPE)
* afterwards.
*
* If the buffer is all zero the return value is equal to len.
*/
static size_t buffer_find_nonzero_offset_inner(const void *buf, size_t len)
{
const VECTYPE *p = buf;
const VECTYPE zero = (VECTYPE){0};
size_t i;
assert(can_use_buffer_find_nonzero_offset_inner(buf, len));
if (!len) {
return 0;
}
for (i = 0; i < BUFFER_FIND_NONZERO_OFFSET_UNROLL_FACTOR; i++) {
if (!ALL_EQ(p[i], zero)) {
return i * sizeof(VECTYPE);
}
}
for (i = BUFFER_FIND_NONZERO_OFFSET_UNROLL_FACTOR;
i < len / sizeof(VECTYPE);
i += BUFFER_FIND_NONZERO_OFFSET_UNROLL_FACTOR) {
VECTYPE tmp0 = VEC_OR(p[i + 0], p[i + 1]);
VECTYPE tmp1 = VEC_OR(p[i + 2], p[i + 3]);
VECTYPE tmp2 = VEC_OR(p[i + 4], p[i + 5]);
VECTYPE tmp3 = VEC_OR(p[i + 6], p[i + 7]);
VECTYPE tmp01 = VEC_OR(tmp0, tmp1);
VECTYPE tmp23 = VEC_OR(tmp2, tmp3);
if (!ALL_EQ(VEC_OR(tmp01, tmp23), zero)) {
break;
}
}
return i * sizeof(VECTYPE);
}
#if defined CONFIG_AVX2_OPT
#ifdef CONFIG_AVX2_OPT
#pragma GCC push_options
#pragma GCC target("avx2")
#include <cpuid.h>
#include <immintrin.h>
#define AVX2_VECTYPE __m256i
#define AVX2_ALL_EQ(v1, v2) \
(_mm256_movemask_epi8(_mm256_cmpeq_epi8(v1, v2)) == 0xFFFFFFFF)
#define AVX2_VEC_OR(v1, v2) (_mm256_or_si256(v1, v2))
static bool
can_use_buffer_find_nonzero_offset_avx2(const void *buf, size_t len)
{
return (len % (BUFFER_FIND_NONZERO_OFFSET_UNROLL_FACTOR
* sizeof(AVX2_VECTYPE)) == 0
&& ((uintptr_t) buf) % sizeof(AVX2_VECTYPE) == 0);
}
static size_t buffer_find_nonzero_offset_avx2(const void *buf, size_t len)
{
const AVX2_VECTYPE *p = buf;
const AVX2_VECTYPE zero = (AVX2_VECTYPE){0};
size_t i;
assert(can_use_buffer_find_nonzero_offset_avx2(buf, len));
if (!len) {
return 0;
}
for (i = 0; i < BUFFER_FIND_NONZERO_OFFSET_UNROLL_FACTOR; i++) {
if (!AVX2_ALL_EQ(p[i], zero)) {
return i * sizeof(AVX2_VECTYPE);
}
}
for (i = BUFFER_FIND_NONZERO_OFFSET_UNROLL_FACTOR;
i < len / sizeof(AVX2_VECTYPE);
i += BUFFER_FIND_NONZERO_OFFSET_UNROLL_FACTOR) {
AVX2_VECTYPE tmp0 = AVX2_VEC_OR(p[i + 0], p[i + 1]);
AVX2_VECTYPE tmp1 = AVX2_VEC_OR(p[i + 2], p[i + 3]);
AVX2_VECTYPE tmp2 = AVX2_VEC_OR(p[i + 4], p[i + 5]);
AVX2_VECTYPE tmp3 = AVX2_VEC_OR(p[i + 6], p[i + 7]);
AVX2_VECTYPE tmp01 = AVX2_VEC_OR(tmp0, tmp1);
AVX2_VECTYPE tmp23 = AVX2_VEC_OR(tmp2, tmp3);
if (!AVX2_ALL_EQ(AVX2_VEC_OR(tmp01, tmp23), zero)) {
break;
}
}
return i * sizeof(AVX2_VECTYPE);
}
static bool avx2_support(void)
{
int a, b, c, d;
if (__get_cpuid_max(0, NULL) < 7) {
return false;
}
__cpuid_count(7, 0, a, b, c, d);
return b & bit_AVX2;
}
static bool can_use_buffer_find_nonzero_offset(const void *buf, size_t len) \
__attribute__ ((ifunc("can_use_buffer_find_nonzero_offset_ifunc")));
static size_t buffer_find_nonzero_offset(const void *buf, size_t len) \
__attribute__ ((ifunc("buffer_find_nonzero_offset_ifunc")));
static void *buffer_find_nonzero_offset_ifunc(void)
{
typeof(buffer_find_nonzero_offset) *func = (avx2_support()) ?
buffer_find_nonzero_offset_avx2 : buffer_find_nonzero_offset_inner;
return func;
}
static void *can_use_buffer_find_nonzero_offset_ifunc(void)
{
typeof(can_use_buffer_find_nonzero_offset) *func = (avx2_support()) ?
can_use_buffer_find_nonzero_offset_avx2 :
can_use_buffer_find_nonzero_offset_inner;
return func;
}
#define AVX2_NONZERO(X) !_mm256_testz_si256((X), (X))
ACCEL_BUFFER_ZERO(buffer_zero_avx2, 128, __m256i, AVX2_NONZERO)
#pragma GCC pop_options
#else
static bool can_use_buffer_find_nonzero_offset(const void *buf, size_t len)
#endif
#define CACHE_AVX2 2
#define CACHE_AVX1 4
#define CACHE_SSE4 8
#define CACHE_SSE2 16
static unsigned cpuid_cache;
static void __attribute__((constructor)) init_cpuid_cache(void)
{
return can_use_buffer_find_nonzero_offset_inner(buf, len);
int max = __get_cpuid_max(0, NULL);
int a, b, c, d;
unsigned cache = 0;
if (max >= 1) {
__cpuid(1, a, b, c, d);
if (d & bit_SSE2) {
cache |= CACHE_SSE2;
}
#ifdef CONFIG_AVX2_OPT
if (c & bit_SSE4_1) {
cache |= CACHE_SSE4;
}
/* We must check that AVX is not just available, but usable. */
if ((c & bit_OSXSAVE) && (c & bit_AVX)) {
__asm("xgetbv" : "=a"(a), "=d"(d) : "c"(0));
if ((a & 6) == 6) {
cache |= CACHE_AVX1;
if (max >= 7) {
__cpuid_count(7, 0, a, b, c, d);
if (b & bit_AVX2) {
cache |= CACHE_AVX2;
}
}
}
}
#endif
}
cpuid_cache = cache;
}
static size_t buffer_find_nonzero_offset(const void *buf, size_t len)
static bool select_accel_fn(const void *buf, size_t len)
{
return buffer_find_nonzero_offset_inner(buf, len);
uintptr_t ibuf = (uintptr_t)buf;
#ifdef CONFIG_AVX2_OPT
if (len % 128 == 0 && ibuf % 32 == 0 && (cpuid_cache & CACHE_AVX2)) {
return buffer_zero_avx2(buf, len);
}
#endif
if (len % 64 == 0 && ibuf % 16 == 0 && (cpuid_cache & CACHE_SSE2)) {
return buffer_zero_sse2(buf, len);
}
return buffer_zero_int(buf, len);
}
#elif defined(__aarch64__)
#include "arm_neon.h"
#define DO_NONZERO(X) (vgetq_lane_u64((X), 0) | vgetq_lane_u64((X), 1))
ACCEL_BUFFER_ZERO(buffer_zero_neon, 128, uint64x2_t, DO_NONZERO)
static bool select_accel_fn(const void *buf, size_t len)
{
uintptr_t ibuf = (uintptr_t)buf;
if (len % 128 == 0 && ibuf % sizeof(uint64x2_t) == 0) {
return buffer_zero_neon(buf, len);
}
return buffer_zero_int(buf, len);
}
#else
#define select_accel_fn buffer_zero_int
#endif
/*
* Checks if a buffer is all zeroes
*
* Attention! The len must be a multiple of 4 * sizeof(long) due to
* restriction of optimizations in this function.
*/
bool buffer_is_zero(const void *buf, size_t len)
{
/*
* Use long as the biggest available internal data type that fits into the
* CPU register and unroll the loop to smooth out the effect of memory
* latency.
*/
size_t i;
long d0, d1, d2, d3;
const long * const data = buf;
/* use vector optimized zero check if possible */
if (can_use_buffer_find_nonzero_offset(buf, len)) {
return buffer_find_nonzero_offset(buf, len) == len;
if (unlikely(len == 0)) {
return true;
}
assert(len % (4 * sizeof(long)) == 0);
len /= sizeof(long);
for (i = 0; i < len; i += 4) {
d0 = data[i + 0];
d1 = data[i + 1];
d2 = data[i + 2];
d3 = data[i + 3];
if (d0 || d1 || d2 || d3) {
return false;
}
}
return true;
/* Use an optimized zero check if possible. Note that this also
includes a check for an unrolled loop over 64-bit integers. */
return select_accel_fn(buf, len);
}