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AVX512 support for xbzrle_encode_buffer

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This commit is the same with [PATCH v6 1/2], and provides avx512 support for xbzrle_encode_buffer
function to accelerate xbzrle encoding speed. Runtime check of avx512
support and benchmark for this feature are added. Compared with C
version of xbzrle_encode_buffer function, avx512 version can achieve
50%-70% performance improvement on benchmarking. In addition, if dirty
data is randomly located in 4K page, the avx512 version can achieve
almost 140% performance gain.

Signed-off-by: ling xu <ling1.xu@intel.com>
Co-authored-by: Zhou Zhao <zhou.zhao@intel.com>
Co-authored-by: Jun Jin <jun.i.jin@intel.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>
This commit is contained in:
ling xu 2022-11-16 23:29:22 +08:00 committed by Juan Quintela
parent e264705012
commit 04ffce137b
6 changed files with 181 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

17
meson.build
View File

@ -2351,6 +2351,22 @@ config_host_data.set('CONFIG_AVX512F_OPT', get_option('avx512f') \
int main(int argc, char *argv[]) { return bar(argv[argc - 1]); }
'''), error_message: 'AVX512F not available').allowed())
config_host_data.set('CONFIG_AVX512BW_OPT', get_option('avx512bw') \
.require(have_cpuid_h, error_message: 'cpuid.h not available, cannot enable AVX512BW') \
.require(cc.links('''
#pragma GCC push_options
#pragma GCC target("avx512bw")
#include <cpuid.h>
#include <immintrin.h>
static int bar(void *a) {
__m512i *x = a;
__m512i res= _mm512_abs_epi8(*x);
return res[1];
}
int main(int argc, char *argv[]) { return bar(argv[0]); }
'''), error_message: 'AVX512BW not available').allowed())
have_pvrdma = get_option('pvrdma') \
.require(rdma.found(), error_message: 'PVRDMA requires OpenFabrics libraries') \
.require(cc.compiles(gnu_source_prefix + '''
@ -3783,6 +3799,7 @@ summary_info += {'debug stack usage': get_option('debug_stack_usage')}
summary_info += {'mutex debugging': get_option('debug_mutex')}
summary_info += {'memory allocator': get_option('malloc')}
summary_info += {'avx2 optimization': config_host_data.get('CONFIG_AVX2_OPT')}
summary_info += {'avx512bw optimization': config_host_data.get('CONFIG_AVX512BW_OPT')}
summary_info += {'avx512f optimization': config_host_data.get('CONFIG_AVX512F_OPT')}
summary_info += {'gprof enabled': get_option('gprof')}
summary_info += {'gcov': get_option('b_coverage')}

2
meson_options.txt
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@ -104,6 +104,8 @@ option('avx2', type: 'feature', value: 'auto',
description: 'AVX2 optimizations')
option('avx512f', type: 'feature', value: 'disabled',
description: 'AVX512F optimizations')
option('avx512bw', type: 'feature', value: 'auto',
description: 'AVX512BW optimizations')
option('keyring', type: 'feature', value: 'auto',
description: 'Linux keyring support')

34
migration/ram.c
View File

@ -83,6 +83,34 @@
/* 0x80 is reserved in migration.h start with 0x100 next */
#define RAM_SAVE_FLAG_COMPRESS_PAGE 0x100
int (*xbzrle_encode_buffer_func)(uint8_t *, uint8_t *, int,
uint8_t *, int) = xbzrle_encode_buffer;
#if defined(CONFIG_AVX512BW_OPT)
#include "qemu/cpuid.h"
static void __attribute__((constructor)) init_cpu_flag(void)
{
unsigned max = __get_cpuid_max(0, NULL);
int a, b, c, d;
if (max >= 1) {
__cpuid(1, a, b, c, d);
/* We must check that AVX is not just available, but usable. */
if ((c & bit_OSXSAVE) && (c & bit_AVX) && max >= 7) {
int bv;
__asm("xgetbv" : "=a"(bv), "=d"(d) : "c"(0));
__cpuid_count(7, 0, a, b, c, d);
/* 0xe6:
* XCR0[7:5] = 111b (OPMASK state, upper 256-bit of ZMM0-ZMM15
* and ZMM16-ZMM31 state are enabled by OS)
* XCR0[2:1] = 11b (XMM state and YMM state are enabled by OS)
*/
if ((bv & 0xe6) == 0xe6 && (b & bit_AVX512BW)) {
xbzrle_encode_buffer_func = xbzrle_encode_buffer_avx512;
}
}
}
}
#endif
XBZRLECacheStats xbzrle_counters;
/* used by the search for pages to send */
@ -806,9 +834,9 @@ static int save_xbzrle_page(RAMState *rs, PageSearchStatus *pss,
memcpy(XBZRLE.current_buf, *current_data, TARGET_PAGE_SIZE);
/* XBZRLE encoding (if there is no overflow) */
encoded_len = xbzrle_encode_buffer(prev_cached_page, XBZRLE.current_buf,
TARGET_PAGE_SIZE, XBZRLE.encoded_buf,
TARGET_PAGE_SIZE);
encoded_len = xbzrle_encode_buffer_func(prev_cached_page, XBZRLE.current_buf,
TARGET_PAGE_SIZE, XBZRLE.encoded_buf,
TARGET_PAGE_SIZE);
/*
* Update the cache contents, so that it corresponds to the data

124
migration/xbzrle.c
View File

@ -174,3 +174,127 @@ int xbzrle_decode_buffer(uint8_t *src, int slen, uint8_t *dst, int dlen)
return d;
}
#if defined(CONFIG_AVX512BW_OPT)
#pragma GCC push_options
#pragma GCC target("avx512bw")
#include <immintrin.h>
int xbzrle_encode_buffer_avx512(uint8_t *old_buf, uint8_t *new_buf, int slen,
uint8_t *dst, int dlen)
{
uint32_t zrun_len = 0, nzrun_len = 0;
int d = 0, i = 0, num = 0;
uint8_t *nzrun_start = NULL;
/* add 1 to include residual part in main loop */
uint32_t count512s = (slen >> 6) + 1;
/* countResidual is tail of data, i.e., countResidual = slen % 64 */
uint32_t count_residual = slen & 0b111111;
bool never_same = true;
uint64_t mask_residual = 1;
mask_residual <<= count_residual;
mask_residual -= 1;
__m512i r = _mm512_set1_epi32(0);
while (count512s) {
if (d + 2 > dlen) {
return -1;
}
int bytes_to_check = 64;
uint64_t mask = 0xffffffffffffffff;
if (count512s == 1) {
bytes_to_check = count_residual;
mask = mask_residual;
}
__m512i old_data = _mm512_mask_loadu_epi8(r,
mask, old_buf + i);
__m512i new_data = _mm512_mask_loadu_epi8(r,
mask, new_buf + i);
uint64_t comp = _mm512_cmpeq_epi8_mask(old_data, new_data);
count512s--;
bool is_same = (comp & 0x1);
while (bytes_to_check) {
if (is_same) {
if (nzrun_len) {
d += uleb128_encode_small(dst + d, nzrun_len);
if (d + nzrun_len > dlen) {
return -1;
}
nzrun_start = new_buf + i - nzrun_len;
memcpy(dst + d, nzrun_start, nzrun_len);
d += nzrun_len;
nzrun_len = 0;
}
/* 64 data at a time for speed */
if (count512s && (comp == 0xffffffffffffffff)) {
i += 64;
zrun_len += 64;
break;
}
never_same = false;
num = __builtin_ctzll(~comp);
num = (num < bytes_to_check) ? num : bytes_to_check;
zrun_len += num;
bytes_to_check -= num;
comp >>= num;
i += num;
if (bytes_to_check) {
/* still has different data after same data */
d += uleb128_encode_small(dst + d, zrun_len);
zrun_len = 0;
} else {
break;
}
}
if (never_same || zrun_len) {
/*
* never_same only acts if
* data begins with diff in first count512s
*/
d += uleb128_encode_small(dst + d, zrun_len);
zrun_len = 0;
never_same = false;
}
/* has diff, 64 data at a time for speed */
if ((bytes_to_check == 64) && (comp == 0x0)) {
i += 64;
nzrun_len += 64;
break;
}
num = __builtin_ctzll(comp);
num = (num < bytes_to_check) ? num : bytes_to_check;
nzrun_len += num;
bytes_to_check -= num;
comp >>= num;
i += num;
if (bytes_to_check) {
/* mask like 111000 */
d += uleb128_encode_small(dst + d, nzrun_len);
/* overflow */
if (d + nzrun_len > dlen) {
return -1;
}
nzrun_start = new_buf + i - nzrun_len;
memcpy(dst + d, nzrun_start, nzrun_len);
d += nzrun_len;
nzrun_len = 0;
is_same = true;
}
}
}
if (nzrun_len != 0) {
d += uleb128_encode_small(dst + d, nzrun_len);
/* overflow */
if (d + nzrun_len > dlen) {
return -1;
}
nzrun_start = new_buf + i - nzrun_len;
memcpy(dst + d, nzrun_start, nzrun_len);
d += nzrun_len;
}
return d;
}
#pragma GCC pop_options
#endif

4
migration/xbzrle.h
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@ -18,4 +18,8 @@ int xbzrle_encode_buffer(uint8_t *old_buf, uint8_t *new_buf, int slen,
uint8_t *dst, int dlen);
int xbzrle_decode_buffer(uint8_t *src, int slen, uint8_t *dst, int dlen);
#if defined(CONFIG_AVX512BW_OPT)
int xbzrle_encode_buffer_avx512(uint8_t *old_buf, uint8_t *new_buf, int slen,
uint8_t *dst, int dlen);
#endif
#endif

3
scripts/meson-buildoptions.sh
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@ -70,6 +70,7 @@ meson_options_help() {
printf "%s\n" ' attr attr/xattr support'
printf "%s\n" ' auth-pam PAM access control'
printf "%s\n" ' avx2 AVX2 optimizations'
printf "%s\n" ' avx512bw AVX512BW optimizations'
printf "%s\n" ' avx512f AVX512F optimizations'
printf "%s\n" ' blkio libblkio block device driver'
printf "%s\n" ' bochs bochs image format support'
@ -198,6 +199,8 @@ _meson_option_parse() {
--disable-auth-pam) printf "%s" -Dauth_pam=disabled ;;
--enable-avx2) printf "%s" -Davx2=enabled ;;
--disable-avx2) printf "%s" -Davx2=disabled ;;
--enable-avx512bw) printf "%s" -Davx512bw=enabled ;;
--disable-avx512bw) printf "%s" -Davx512bw=disabled ;;
--enable-avx512f) printf "%s" -Davx512f=enabled ;;
--disable-avx512f) printf "%s" -Davx512f=disabled ;;
--enable-gcov) printf "%s" -Db_coverage=true ;;