Paolo Bonzini
87b8bde55d
This reverts commit b18236897c.
The x86-64 instruction set can now be tuned down to x86-64 v1
or i386 Pentium Pro.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
126 lines
3.4 KiB
C++
126 lines
3.4 KiB
C++
/*
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* SPDX-License-Identifier: GPL-2.0-or-later
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* buffer_is_zero acceleration, x86 version.
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*/
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#if defined(CONFIG_AVX2_OPT) || defined(__SSE2__)
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#include <immintrin.h>
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/* Helper for preventing the compiler from reassociating
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chains of binary vector operations. */
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#define SSE_REASSOC_BARRIER(vec0, vec1) asm("" : "+x"(vec0), "+x"(vec1))
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/* Note that these vectorized functions may assume len >= 256. */
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static bool __attribute__((target("sse2")))
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buffer_zero_sse2(const void *buf, size_t len)
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{
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/* Unaligned loads at head/tail. */
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__m128i v = *(__m128i_u *)(buf);
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__m128i w = *(__m128i_u *)(buf + len - 16);
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/* Align head/tail to 16-byte boundaries. */
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const __m128i *p = QEMU_ALIGN_PTR_DOWN(buf + 16, 16);
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const __m128i *e = QEMU_ALIGN_PTR_DOWN(buf + len - 1, 16);
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__m128i zero = { 0 };
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/* Collect a partial block at tail end. */
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v |= e[-1]; w |= e[-2];
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SSE_REASSOC_BARRIER(v, w);
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v |= e[-3]; w |= e[-4];
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SSE_REASSOC_BARRIER(v, w);
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v |= e[-5]; w |= e[-6];
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SSE_REASSOC_BARRIER(v, w);
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v |= e[-7]; v |= w;
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/*
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* Loop over complete 128-byte blocks.
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* With the head and tail removed, e - p >= 14, so the loop
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* must iterate at least once.
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*/
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do {
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v = _mm_cmpeq_epi8(v, zero);
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if (unlikely(_mm_movemask_epi8(v) != 0xFFFF)) {
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return false;
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}
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v = p[0]; w = p[1];
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SSE_REASSOC_BARRIER(v, w);
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v |= p[2]; w |= p[3];
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SSE_REASSOC_BARRIER(v, w);
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v |= p[4]; w |= p[5];
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SSE_REASSOC_BARRIER(v, w);
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v |= p[6]; w |= p[7];
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SSE_REASSOC_BARRIER(v, w);
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v |= w;
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p += 8;
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} while (p < e - 7);
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return _mm_movemask_epi8(_mm_cmpeq_epi8(v, zero)) == 0xFFFF;
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}
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#ifdef CONFIG_AVX2_OPT
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static bool __attribute__((target("avx2")))
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buffer_zero_avx2(const void *buf, size_t len)
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{
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/* Unaligned loads at head/tail. */
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__m256i v = *(__m256i_u *)(buf);
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__m256i w = *(__m256i_u *)(buf + len - 32);
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/* Align head/tail to 32-byte boundaries. */
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const __m256i *p = QEMU_ALIGN_PTR_DOWN(buf + 32, 32);
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const __m256i *e = QEMU_ALIGN_PTR_DOWN(buf + len - 1, 32);
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__m256i zero = { 0 };
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/* Collect a partial block at tail end. */
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v |= e[-1]; w |= e[-2];
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SSE_REASSOC_BARRIER(v, w);
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v |= e[-3]; w |= e[-4];
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SSE_REASSOC_BARRIER(v, w);
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v |= e[-5]; w |= e[-6];
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SSE_REASSOC_BARRIER(v, w);
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v |= e[-7]; v |= w;
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/* Loop over complete 256-byte blocks. */
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for (; p < e - 7; p += 8) {
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/* PTEST is not profitable here. */
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v = _mm256_cmpeq_epi8(v, zero);
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if (unlikely(_mm256_movemask_epi8(v) != 0xFFFFFFFF)) {
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return false;
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}
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v = p[0]; w = p[1];
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SSE_REASSOC_BARRIER(v, w);
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v |= p[2]; w |= p[3];
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SSE_REASSOC_BARRIER(v, w);
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v |= p[4]; w |= p[5];
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SSE_REASSOC_BARRIER(v, w);
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v |= p[6]; w |= p[7];
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SSE_REASSOC_BARRIER(v, w);
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v |= w;
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}
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return _mm256_movemask_epi8(_mm256_cmpeq_epi8(v, zero)) == 0xFFFFFFFF;
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}
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#endif /* CONFIG_AVX2_OPT */
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static biz_accel_fn const accel_table[] = {
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buffer_is_zero_int_ge256,
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buffer_zero_sse2,
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#ifdef CONFIG_AVX2_OPT
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buffer_zero_avx2,
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#endif
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};
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static unsigned best_accel(void)
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{
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unsigned info = cpuinfo_init();
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#ifdef CONFIG_AVX2_OPT
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if (info & CPUINFO_AVX2) {
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return 2;
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}
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#endif
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return info & CPUINFO_SSE2 ? 1 : 0;
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}
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#else
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# include "host/include/generic/host/bufferiszero.c.inc"
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#endif
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