[PATCH] SSE2/SSSE3 optimized version of get_checksum1() for x86-64
Filipe Maia
filipe.c.maia at gmail.com
Mon May 18 15:42:16 UTC 2020
I think this is a great patch but, in my view, an even better way to tackle
the fundamental problem (the performance limitations) is to use a much
faster checksum like xxhash, as has been suggested before:
https://lists.samba.org/archive/rsync/2019-October/031975.html
Cheers,
Filipe
On Mon, 18 May 2020 at 17:08, Jorrit Jongma via rsync <rsync at lists.samba.org>
wrote:
> This drop-in patch increases the performance of the get_checksum1()
> function on x86-64.
>
> On the target slow CPU performance of the function increased by nearly
> 50% in the x86-64 default SSE2 mode, and by nearly 100% if the
> compiler was told to enable SSSE3 support. The increase was over 200%
> on the fastest CPU tested in SSSE3 mode.
>
> Transfer time improvement with large files existing on both ends but
> with some bits flipped was measured as 5-10%, with the target machine
> being CPU limited (still so due to MD5).
>
> This same patch on (my) GitHub for easier reading:
>
> https://github.com/Chainfire/rsync/commit/f5d0b32df869a23a74b8b8295e4983b0943866df
>
>
> From f5d0b32df869a23a74b8b8295e4983b0943866df Mon Sep 17 00:00:00 2001
> From: Jorrit Jongma <git at jongma.org>
> Date: Mon, 18 May 2020 00:21:39 +0200
> Subject: [PATCH 1/1] SSE2/SSSE3 optimized version of get_checksum1() for
> x86-64
>
> ---
> Makefile.in | 2 +-
> checksum.c | 2 +
> checksum_sse2.c | 243 ++++++++++++++++++++++++++++++++++++++++++++++++
> 3 files changed, 246 insertions(+), 1 deletion(-)
> create mode 100644 checksum_sse2.c
>
> diff --git a/Makefile.in b/Makefile.in
> index 59649562..e4202336 100644
> --- a/Makefile.in
> +++ b/Makefile.in
> @@ -40,7 +40,7 @@ OBJS1=flist.o rsync.o generator.o receiver.o
> cleanup.o sender.o exclude.o \
> util.o util2.o main.o checksum.o match.o syscall.o log.o backup.o
> delete.o
> OBJS2=options.o io.o compat.o hlink.o token.o uidlist.o socket.o
> hashtable.o \
> fileio.o batch.o clientname.o chmod.o acls.o xattrs.o
> -OBJS3=progress.o pipe.o
> +OBJS3=progress.o pipe.o checksum_sse2.o
> DAEMON_OBJ = params.o loadparm.o clientserver.o access.o connection.o
> authenticate.o
> popt_OBJS=popt/findme.o popt/popt.o popt/poptconfig.o \
> popt/popthelp.o popt/poptparse.o
> diff --git a/checksum.c b/checksum.c
> index cd234038..4e696f3d 100644
> --- a/checksum.c
> +++ b/checksum.c
> @@ -99,6 +99,7 @@ int canonical_checksum(int csum_type)
> return csum_type >= CSUM_MD4 ? 1 : 0;
> }
>
> +#ifndef __SSE2__ // see checksum_sse2.c for SSE2/SSSE3 version
> /*
> a simple 32 bit checksum that can be updated from either end
> (inspired by Mark Adler's Adler-32 checksum)
> @@ -119,6 +120,7 @@ uint32 get_checksum1(char *buf1, int32 len)
> }
> return (s1 & 0xffff) + (s2 << 16);
> }
> +#endif
>
> void get_checksum2(char *buf, int32 len, char *sum)
> {
> diff --git a/checksum_sse2.c b/checksum_sse2.c
> new file mode 100644
> index 00000000..51662833
> --- /dev/null
> +++ b/checksum_sse2.c
> @@ -0,0 +1,243 @@
> +/*
> + * SSE2/SSSE3-optimized routines to support checksumming of bytes.
> + *
> + * Copyright (C) 1996 Andrew Tridgell
> + * Copyright (C) 1996 Paul Mackerras
> + * Copyright (C) 2004-2020 Wayne Davison
> + * Copyright (C) 2020 Jorrit Jongma
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License as published by
> + * the Free Software Foundation; either version 3 of the License, or
> + * (at your option) any later version.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> + * GNU General Public License for more details.
> + *
> + * You should have received a copy of the GNU General Public License along
> + * with this program; if not, visit the http://fsf.org website.
> + */
> +/*
> + * Optimization target for get_checksum1 was the Intel Atom D2700, the
> + * slowest CPU in the test set and the most likely to be CPU limited
> during
> + * transfers. The combination of intrinsics was chosen specifically for
> the
> + * most gain on that CPU, other combinations were occasionally slightly
> + * faster on the others.
> + *
> + * While on more modern CPUs transfers are less likely to be CPU limited,
> + * lower CPU usage is always better. Improvements may still be seen when
> + * matching chunks from NVMe storage even on newer CPUs.
> + *
> + * Benchmarks C SSE2 SSSE3
> + * - Intel Atom D2700 550 MB/s 750 MB/s 1000 MB/s
> + * - Intel i7-7700hq 1850 MB/s 2550 MB/s 4050 MB/s
> + * - AMD ThreadRipper 2950x 2900 MB/s 5600 MB/s 8950 MB/s
> + *
> + * This optimization for get_checksum1 is intentionally limited to x86-64
> as
> + * no 32-bit CPU was available for testing. As 32-bit CPUs only have half
> the
> + * available xmm registers, this optimized version may not be faster than
> the
> + * pure C version anyway.
> + *
> + * GCC automatically enables SSE2 support on x86-64 builds. The SSSE3 code
> + * path must be enabled manually: ./configure CFLAGS="-mssse3 -O2"
> + */
> +
> +#ifdef __x86_64__
> +#ifdef __SSE2__
> +
> +#include "rsync.h"
> +
> +#ifdef __SSSE3__
> +#include <immintrin.h>
> +#else
> +#include <tmmintrin.h>
> +#endif
> +
> +/* Compatibility functions to let our SSSE3 algorithm run on SSE2 */
> +
> +static inline __m128i sse_load_si128(void const* buf) {
> +#ifdef __SSSE3__
> + return _mm_lddqu_si128(buf); // same as loadu on all but the
> oldest SSSE3 CPUs
> +#else
> + return _mm_loadu_si128(buf);
> +#endif
> +}
> +
> +#ifndef __SSSE3__
> +static inline __m128i sse_interleave_odd_epi16(__m128i a, __m128i b) {
> + return _mm_packs_epi32(
> + _mm_srai_epi32(a, 16),
> + _mm_srai_epi32(b, 16)
> + );
> +}
> +
> +static inline __m128i sse_interleave_even_epi16(__m128i a, __m128i b) {
> + return sse_interleave_odd_epi16(
> + _mm_slli_si128(a, 2),
> + _mm_slli_si128(b, 2)
> + );
> +}
> +
> +static inline __m128i sse_mulu_odd_epi8(__m128i a, __m128i b) {
> + return _mm_mullo_epi16(
> + _mm_srli_epi16(a, 8),
> + _mm_srai_epi16(b, 8)
> + );
> +}
> +
> +static inline __m128i sse_mulu_even_epi8(__m128i a, __m128i b) {
> + return _mm_mullo_epi16(
> + _mm_and_si128(a, _mm_set1_epi16(0xFF)),
> + _mm_srai_epi16(_mm_slli_si128(b, 1), 8)
> + );
> +}
> +#endif
> +
> +static inline __m128i sse_hadds_epi16(__m128i a, __m128i b) {
> +#ifdef __SSSE3__
> + return _mm_hadds_epi16(a, b);
> +#else
> + return _mm_adds_epi16(
> + sse_interleave_even_epi16(a, b),
> + sse_interleave_odd_epi16(a, b)
> + );
> +#endif
> +}
> +
> +static inline __m128i sse_maddubs_epi16(__m128i a, __m128i b) {
> +#ifdef __SSSE3__
> + return _mm_maddubs_epi16(a, b);
> +#else
> + return _mm_adds_epi16(
> + sse_mulu_even_epi8(a, b),
> + sse_mulu_odd_epi8(a, b)
> + );
> +#endif
> +}
> +
> +/*
> + a simple 32 bit checksum that can be updated from either end
> + (inspired by Mark Adler's Adler-32 checksum)
> + */
> +/*
> + Original loop per 4 bytes:
> + s2 += 4*(s1 + buf[i]) + 3*buf[i+1] + 2*buf[i+2] + buf[i+3] +
> 10*CHAR_OFFSET;
> + s1 += buf[i] + buf[i+1] + buf[i+2] + buf[i+3] + 4*CHAR_OFFSET;
> +
> + SSE2/SSSE3 loop per 32 bytes:
> + int16 t1[8];
> + int16 t2[8];
> + for (int j = 0; j < 8; j++) {
> + t1[j] = buf[j*4 + i] + buf[j*4 + i+1] + buf[j*4 + i+2] + buf[j*4 +
> i+3];
> + t2[j] = 4*buf[j*4 + i] + 3*buf[j*4 + i+1] + 2*buf[j*4 + i+2] +
> buf[j*4 + i+3];
> + }
> + s2 += 32*s1 +
> + 28*t1[0] + 24*t1[1] + 20*t1[2] + 16*t1[3] + 12*t1[4] +
> 8*t1[5] + 4*t1[6] +
> + t2[0] + t2[1] + t2[2] + t2[3] + t2[4] + t2[5] + t2[6] + t2[7] +
> + ((16+32+48+64+80+96) + 8)*CHAR_OFFSET;
> + s1 += t1[0] + t1[1] + t1[2] + t1[3] + t1[4] + t1[5] + t1[6] + t1[7] +
> + 32*CHAR_OFFSET;
> + */
> +uint32 get_checksum1(char *buf1, int32 len)
> +{
> + int32 i;
> + uint32 s1, s2;
> + schar *buf = (schar *)buf1;
> +
> + i = s1 = s2 = 0;
> + if (len > 32) {
> + const char mul_t1_buf[16] = {28, 0, 24, 0, 20, 0, 16, 0, 12,
> 0, 8, 0, 4, 0, 0, 0};
> + __m128i mul_t1 = sse_load_si128((void const*)mul_t1_buf);
> + __m128i ss1 = _mm_setzero_si128();
> + __m128i ss2 = _mm_setzero_si128();
> +
> + for (i = 0; i < (len-32); i+=32) {
> + // Load ... 2*[int8*16]
> + __m128i in8_1 = sse_load_si128((void const*)&buf[i]);
> + __m128i in8_2 = sse_load_si128((void const*)&buf[i + 16]);
> +
> + // (1*buf[i] + 1*buf[i+1]), (1*buf[i+2], 1*buf[i+3]), ...
> 2*[int16*8]
> + // Fastest, even though multiply by 1
> + __m128i mul_one = _mm_set1_epi8(1);
> + __m128i add16_1 = sse_maddubs_epi16(mul_one, in8_1);
> + __m128i add16_2 = sse_maddubs_epi16(mul_one, in8_2);
> +
> + // (4*buf[i] + 3*buf[i+1]), (2*buf[i+2], buf[i+3]), ...
> 2*[int16*8]
> + __m128i mul_const = _mm_set1_epi32(4 + (3 << 8) + (2 <<
> 16) + (1 << 24));
> + __m128i mul_add16_1 = sse_maddubs_epi16(mul_const, in8_1);
> + __m128i mul_add16_2 = sse_maddubs_epi16(mul_const, in8_2);
> +
> + // s2 += 32*s1
> + ss2 = _mm_add_epi32(ss2, _mm_slli_epi32(ss1, 5));
> +
> + // [sum(t1[0]..t1[6]), X, X, X] [int32*4]; faster than
> multiple _mm_hadds_epi16
> + // Shifting left, then shifting right again and shuffling
> (rather than just
> + // shifting right as with mul32 below) to cheaply end up
> with the correct sign
> + // extension as we go from int16 to int32.
> + __m128i sum_add32 = _mm_add_epi16(add16_1, add16_2);
> + sum_add32 = _mm_add_epi16(sum_add32,
> _mm_slli_si128(sum_add32, 2));
> + sum_add32 = _mm_add_epi16(sum_add32,
> _mm_slli_si128(sum_add32, 4));
> + sum_add32 = _mm_add_epi16(sum_add32,
> _mm_slli_si128(sum_add32, 8));
> + sum_add32 = _mm_srai_epi32(sum_add32, 16);
> + sum_add32 = _mm_shuffle_epi32(sum_add32, 3);
> +
> + // [sum(t2[0]..t2[6]), X, X, X] [int32*4]; faster than
> multiple _mm_hadds_epi16
> + __m128i sum_mul_add32 = _mm_add_epi16(mul_add16_1,
> mul_add16_2);
> + sum_mul_add32 = _mm_add_epi16(sum_mul_add32,
> _mm_slli_si128(sum_mul_add32, 2));
> + sum_mul_add32 = _mm_add_epi16(sum_mul_add32,
> _mm_slli_si128(sum_mul_add32, 4));
> + sum_mul_add32 = _mm_add_epi16(sum_mul_add32,
> _mm_slli_si128(sum_mul_add32, 8));
> + sum_mul_add32 = _mm_srai_epi32(sum_mul_add32, 16);
> + sum_mul_add32 = _mm_shuffle_epi32(sum_mul_add32, 3);
> +
> + // s1 += t1[0] + t1[1] + t1[2] + t1[3] + t1[4] + t1[5] +
> t1[6] + t1[7]
> + ss1 = _mm_add_epi32(ss1, sum_add32);
> +
> + // s2 += t2[0] + t2[1] + t2[2] + t2[3] + t2[4] + t2[5] +
> t2[6] + t2[7]
> + ss2 = _mm_add_epi32(ss2, sum_mul_add32);
> +
> + // [t1[0], t1[1], ...] [int16*8]
> + // We could've combined this with generating sum_add32
> above and save one _mm_add_epi16,
> + // but benchmarking shows that as being slower
> + __m128i add16 = sse_hadds_epi16(add16_1, add16_2);
> +
> + // [t1[0], t1[1], ...] -> [t1[0]*28 + t1[1]*24, ...] [int32*4]
> + __m128i mul32 = _mm_madd_epi16(add16, mul_t1);
> +
> + // [sum(mul32), X, X, X] [int32*4]; faster than multiple
> _mm_hadd_epi32
> + mul32 = _mm_add_epi32(mul32, _mm_srli_si128(mul32, 4));
> + mul32 = _mm_add_epi32(mul32, _mm_srli_si128(mul32, 8));
> +
> + // s2 += 28*t1[0] + 24*t1[1] + 20*t1[2] + 16*t1[3] +
> 12*t1[4] + 8*t1[5] + 4*t1[6]
> + ss2 = _mm_add_epi32(ss2, mul32);
> +
> +#if CHAR_OFFSET != 0
> + // s1 += 32*CHAR_OFFSET
> + __m128i char_offset_multiplier = _mm_set1_epi32(32 *
> CHAR_OFFSET);
> + ss1 = _mm_add_epi32(ss1, char_offset_multiplier);
> +
> + // s2 += 528*CHAR_OFFSET
> + char_offset_multiplier = _mm_set1_epi32(528 * CHAR_OFFSET);
> + ss2 = _mm_add_epi32(ss2, char_offset_multiplier);
> +#endif
> + }
> +
> + int32 x[4] = {0};
> + _mm_store_si128((void*)x, ss1);
> + s1 = x[0];
> + _mm_store_si128((void*)x, ss2);
> + s2 = x[0];
> + }
> + for (; i < (len-4); i+=4) {
> + s2 += 4*(s1 + buf[i]) + 3*buf[i+1] + 2*buf[i+2] + buf[i+3] +
> 10*CHAR_OFFSET;
> + s1 += (buf[i] + buf[i+1] + buf[i+2] + buf[i+3] + 4*CHAR_OFFSET);
> + }
> + for (; i < len; i++) {
> + s1 += (buf[i]+CHAR_OFFSET); s2 += s1;
> + }
> + return (s1 & 0xffff) + (s2 << 16);
> +}
> +
> +#endif
> +#endif
> --
> 2.25.2
>
> --
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