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util/bufferiszero: improve avx2 accelerator 

By increasing avx2 length_to_accel to 128, we can simplify its logic and reduce a
branch.

The authorship of this patch actually belongs to Richard Henderson
<richard.henderson@linaro.org>, I just fixed a boundary case on his
original patch.

Suggested-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Robert Hoo <robert.hu@linux.intel.com>
Message-Id: <1585119021-46593-2-git-send-email-robert.hu@linux.intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Robert Hoo 2020-03-25 14:50:21 +08:00 committed by Paolo Bonzini
parent b87c99d073
commit 8f13a39dc0
1 changed files with 9 additions and 17 deletions
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26
util/bufferiszero.c
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@ -158,27 +158,19 @@ buffer_zero_avx2(const void *buf, size_t len)
__m256i *p = (__m256i *)(((uintptr_t)buf + 5 * 32) & -32);
__m256i *e = (__m256i *)(((uintptr_t)buf + len) & -32);
if (likely(p <= e)) {
/* Loop over 32-byte aligned blocks of 128. */
do {
__builtin_prefetch(p);
if (unlikely(!_mm256_testz_si256(t, t))) {
return false;
}
t = p[-4] | p[-3] | p[-2] | p[-1];
p += 4;
} while (p <= e);
} else {
t |= _mm256_loadu_si256(buf + 32);
if (len <= 128) {
goto last2;
/* Loop over 32-byte aligned blocks of 128. */
while (p <= e) {
__builtin_prefetch(p);
if (unlikely(!_mm256_testz_si256(t, t))) {
return false;
}
}
t = p[-4] | p[-3] | p[-2] | p[-1];
p += 4;
} ;
/* Finish the last block of 128 unaligned. */
t |= _mm256_loadu_si256(buf + len - 4 * 32);
t |= _mm256_loadu_si256(buf + len - 3 * 32);
last2:
t |= _mm256_loadu_si256(buf + len - 2 * 32);
t |= _mm256_loadu_si256(buf + len - 1 * 32);
@ -263,7 +255,7 @@ static void init_accel(unsigned cache)
}
if (cache & CACHE_AVX2) {
fn = buffer_zero_avx2;
length_to_accel = 64;
length_to_accel = 128;
}
#endif
#ifdef CONFIG_AVX512F_OPT