ling xu <ling1...@intel.com> wrote:
> This commit update runtime check of AVX512, and implements avx512 of
> xbzrle_encode_buffer function to accelerate xbzrle encoding speed.
> Compared with C version of xbzrle_encode_buffer function, avx512 version
> can achieve almost 60%-70% performance improvement on unit test provided
> by Qemu. In addition, we provide one more unit test called
> "test_encode_decode_random", in which dirty data are randomly located in
> 4K page, and this case can achieve almost 140% performance gain.
>
> Signed-off-by: ling xu <ling1...@intel.com>
> Co-authored-by: Zhou Zhao <zhou.z...@intel.com>
> Co-authored-by: Jun Jin <jun.i....@intel.com>
> ---
> meson.build | 16 ++++
> meson_options.txt | 2 +
> migration/ram.c | 41 ++++++++++
> migration/xbzrle.c | 181 +++++++++++++++++++++++++++++++++++++++++++++
> migration/xbzrle.h | 4 +
> 5 files changed, 244 insertions(+)
>
> diff --git a/meson.build b/meson.build
> index 294e9a8f32..4222b77e9f 100644
> --- a/meson.build
> +++ b/meson.build
> @@ -2262,6 +2262,22 @@ config_host_data.set('CONFIG_AVX512F_OPT',
> get_option('avx512f') \
> int main(int argc, char *argv[]) { return bar(argv[0]); }
> '''), 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 = *(__m512i *)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 + '''
> diff --git a/meson_options.txt b/meson_options.txt
> index e58e158396..07194bf680 100644
> --- a/meson_options.txt
> +++ b/meson_options.txt
> @@ -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')
>
[no clue about meson, it looks ok]
> diff --git a/migration/ram.c b/migration/ram.c
> index dc1de9ddbc..d9c1ac2f7a 100644
> --- a/migration/ram.c
> +++ b/migration/ram.c
> @@ -83,6 +83,35 @@
> /* 0x80 is reserved in migration.h start with 0x100 next */
> #define RAM_SAVE_FLAG_COMPRESS_PAGE 0x100
>
> +#if defined(CONFIG_AVX512BW_OPT)
> +static bool IS_CPU_SUPPORT_AVX512BW;
An all caps global variable?
> +#include "qemu/cpuid.h"
> +static void __attribute__((constructor)) init_cpu_flag(void)
> +{
> + unsigned max = __get_cpuid_max(0, NULL);
> + int a, b, c, d;
> + IS_CPU_SUPPORT_AVX512BW = false;
> + 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)) {
> + IS_CPU_SUPPORT_AVX512BW = true;
> + }
> + }
> + }
> + return ;
> +}
> +#endif
> +
> XBZRLECacheStats xbzrle_counters;
>
> /* struct contains XBZRLE cache and a static page
> @@ -802,9 +831,21 @@ static int save_xbzrle_page(RAMState *rs, uint8_t
> **current_data,
> memcpy(XBZRLE.current_buf, *current_data, TARGET_PAGE_SIZE);
>
> /* XBZRLE encoding (if there is no overflow) */
> + #if defined(CONFIG_AVX512BW_OPT)
> + if (likely(IS_CPU_SUPPORT_AVX512BW)) {
All distributions are go to have compile time support for AVX, but I am
not sure the percentage of machines that support avx
> + encoded_len = xbzrle_encode_buffer_512(prev_cached_page,
> XBZRLE.current_buf,
> + TARGET_PAGE_SIZE,
> XBZRLE.encoded_buf,
> + TARGET_PAGE_SIZE);
> + } else {
> + encoded_len = xbzrle_encode_buffer(prev_cached_page,
> XBZRLE.current_buf,
> + TARGET_PAGE_SIZE,
> XBZRLE.encoded_buf,
> + TARGET_PAGE_SIZE);
> + }
the else part is the same than the #else part
> + #else
> encoded_len = xbzrle_encode_buffer(prev_cached_page, XBZRLE.current_buf,
> TARGET_PAGE_SIZE, XBZRLE.encoded_buf,
> TARGET_PAGE_SIZE);
> + #endif
So, why don't just create a new function pointer:
int (*xbzrle_encode_buffer_func)(uint8_t *old_buf, uint8_t *new_buf, int slen,
uint8_t *dst, int dlen) = xbzrle_encode_buffer;
And aad into init_cpu_flag() something in the line of:
xbzrle_encode_buffer_func = xbrrle_encode_buffer_512;
?
> /*
> * Update the cache contents, so that it corresponds to the data
> diff --git a/migration/xbzrle.c b/migration/xbzrle.c
> index 1ba482ded9..4db09fdbdb 100644
> --- a/migration/xbzrle.c
> +++ b/migration/xbzrle.c
> @@ -174,3 +174,184 @@ 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>
> +#include <math.h>
> +#define SET_ZERO512(r) r = _mm512_set1_epi32(0)
> +int xbzrle_encode_buffer_512(uint8_t *old_buf, uint8_t *new_buf, int slen,
> + uint8_t *dst, int dlen)
> +{
This is just personal taste, but I would rename this to:
xbzrle_encode_buffer_avx512?
> + uint32_t zrun_len = 0, nzrun_len = 0;
> + int d = 0, i = 0, num = 0;
> + uint8_t *nzrun_start = NULL;
> + int count512s = (slen >> 6);
> + int res = slen % 64;
res variable here means residual, normally we use "res" with meaning of
"result" in qemu.
> + bool never_same = true;
> + while (count512s--) {
> + if (d + 2 > dlen) {
> + return -1;
> + }
> + __m512i old_data = _mm512_mask_loadu_epi8(old_data,
> + 0xffffffffffffffff, old_buf + i);
> + __m512i new_data = _mm512_mask_loadu_epi8(new_data,
> + 0xffffffffffffffff, new_buf
> + i);
> + /* in mask bit 1 for same, 0 for diff */
> + __mmask64 comp = _mm512_cmpeq_epi8_mask(old_data, new_data);
> +
> + int bytesToCheck = 64;
> + bool is_same = (comp & 0x1);
> + while (bytesToCheck) {
> + 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;
> + }
> + if (comp == 0xffffffffffffffff) {
> + i += 64;
> + zrun_len += 64;
> + break;
> + }
> + never_same = false;
> + num = __builtin_ctzl(~comp);
> + num = (num < bytesToCheck) ? num : bytesToCheck;
> + zrun_len += num;
> + bytesToCheck -= num;
> + comp >>= num;
> + i += num;
> + if (bytesToCheck) {
> + /* 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 */
> + if ((bytesToCheck == 64) && (comp == 0x0)) {
> + i += 64;
> + nzrun_len += 64;
> + break;
> + }
> + num = __builtin_ctzl(comp);
> + num = (num < bytesToCheck) ? num : bytesToCheck;
> + nzrun_len += num;
> + bytesToCheck -= num;
> + comp >>= num;
> + i += num;
> + if (bytesToCheck) {
> + /* 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 (res) {
> + /* the number of data is less than 64 */
> + unsigned long long mask = pow(2, res);
Not your fault.
21st century. Someone still use long long in a new API, sniff.
> + mask -= 1;
> + __m512i r = SET_ZERO512(r);
> + __m512i old_data = _mm512_mask_loadu_epi8(r, mask, old_buf + i);
> + __m512i new_data = _mm512_mask_loadu_epi8(r, mask, new_buf + i);
> + __mmask64 comp = _mm512_cmpeq_epi8_mask(old_data, new_data);
> +
> + int bytesToCheck = res;
> + bool is_same = (comp & 0x1);
> + while (bytesToCheck) {
> + 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;
> + }
> + never_same = false;
> + num = __builtin_ctzl(~comp);
> + num = (num < bytesToCheck) ? num : bytesToCheck;
> + zrun_len += num;
> + bytesToCheck -= num;
> + comp >>= num;
> + i += num;
> + if (bytesToCheck) {
> + /* diff after same */
> + d += uleb128_encode_small(dst + d, zrun_len);
> + zrun_len = 0;
> + } else {
> + break;
> + }
> + }
> +
> + if (never_same || zrun_len) {
> + d += uleb128_encode_small(dst + d, zrun_len);
> + zrun_len = 0;
> + never_same = false;
> + }
> + /* has diff */
> + num = __builtin_ctzl(comp);
> + num = (num < bytesToCheck) ? num : bytesToCheck;
> + nzrun_len += num;
> + bytesToCheck -= num;
> + comp >>= num;
> + i += num;
> + if (bytesToCheck) {
> + 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 (zrun_len) {
> + return (zrun_len == slen) ? 0 : d;
> + }
> + 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
> \ No newline at end of file
> diff --git a/migration/xbzrle.h b/migration/xbzrle.h
> index a0db507b9c..6247de5f00 100644
> --- a/migration/xbzrle.h
> +++ b/migration/xbzrle.h
> @@ -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_512(uint8_t *old_buf, uint8_t *new_buf, int slen,
> + uint8_t *dst, int dlen);
> +#endif
> #endif
