From: Noah Goldstein <goldstein.w.n@gmail.com>
To: libc-alpha@sourceware.org
Subject: [PATCH v2] x86: Cleanup bounds checking in large memcpy case
Date: Tue, 14 Jun 2022 20:57:09 -0700 [thread overview]
Message-ID: <20220615035709.609517-1-goldstein.w.n@gmail.com> (raw)
In-Reply-To: <20220615002533.1741934-2-goldstein.w.n@gmail.com>
1. Fix incorrect lower-bound threshold in L(large_memcpy_2x).
Previously was using `__x86_rep_movsb_threshold` and should
have been using `__x86_shared_non_temporal_threshold`.
2. Avoid reloading __x86_shared_non_temporal_threshold before
the L(large_memcpy_4x) bounds check.
3. Document the second bounds check for L(large_memcpy_4x)
more clearly.
---
manual/tunables.texi | 2 +-
sysdeps/x86/dl-cacheinfo.h | 2 +-
.../multiarch/memmove-vec-unaligned-erms.S | 29 ++++++++++++++-----
3 files changed, 23 insertions(+), 10 deletions(-)
diff --git a/manual/tunables.texi b/manual/tunables.texi
index 1482412078..49daf3eb4a 100644
--- a/manual/tunables.texi
+++ b/manual/tunables.texi
@@ -47,7 +47,7 @@ glibc.malloc.mxfast: 0x0 (min: 0x0, max: 0xffffffffffffffff)
glibc.elision.skip_lock_busy: 3 (min: -2147483648, max: 2147483647)
glibc.malloc.top_pad: 0x0 (min: 0x0, max: 0xffffffffffffffff)
glibc.cpu.x86_rep_stosb_threshold: 0x800 (min: 0x1, max: 0xffffffffffffffff)
-glibc.cpu.x86_non_temporal_threshold: 0xc0000 (min: 0x0, max: 0xffffffffffffffff)
+glibc.cpu.x86_non_temporal_threshold: 0xc0000 (min: 0x0, max: 0x0fffffffffffffff)
glibc.cpu.x86_shstk:
glibc.cpu.hwcap_mask: 0x6 (min: 0x0, max: 0xffffffffffffffff)
glibc.malloc.mmap_max: 0 (min: -2147483648, max: 2147483647)
diff --git a/sysdeps/x86/dl-cacheinfo.h b/sysdeps/x86/dl-cacheinfo.h
index cc3b840f9c..858ff8a135 100644
--- a/sysdeps/x86/dl-cacheinfo.h
+++ b/sysdeps/x86/dl-cacheinfo.h
@@ -932,7 +932,7 @@ dl_init_cacheinfo (struct cpu_features *cpu_features)
TUNABLE_SET_WITH_BOUNDS (x86_data_cache_size, data, 0, SIZE_MAX);
TUNABLE_SET_WITH_BOUNDS (x86_shared_cache_size, shared, 0, SIZE_MAX);
TUNABLE_SET_WITH_BOUNDS (x86_non_temporal_threshold, non_temporal_threshold,
- 0, SIZE_MAX);
+ 0, SIZE_MAX >> 4);
TUNABLE_SET_WITH_BOUNDS (x86_rep_movsb_threshold, rep_movsb_threshold,
minimum_rep_movsb_threshold, SIZE_MAX);
TUNABLE_SET_WITH_BOUNDS (x86_rep_stosb_threshold, rep_stosb_threshold, 1,
diff --git a/sysdeps/x86_64/multiarch/memmove-vec-unaligned-erms.S b/sysdeps/x86_64/multiarch/memmove-vec-unaligned-erms.S
index af51177d5d..d1518b8bab 100644
--- a/sysdeps/x86_64/multiarch/memmove-vec-unaligned-erms.S
+++ b/sysdeps/x86_64/multiarch/memmove-vec-unaligned-erms.S
@@ -118,7 +118,13 @@
# define LARGE_LOAD_SIZE (VEC_SIZE * 4)
#endif
-/* Amount to shift rdx by to compare for memcpy_large_4x. */
+/* Amount to shift __x86_shared_non_temporal_threshold by for
+ bound for memcpy_large_4x. This is essentially use to to
+ indicate that the copy is far beyond the scope of L3
+ (assuming no user config x86_non_temporal_threshold) and to
+ use a more aggressively unrolled loop. NB: before
+ increasing the value also update initialization of
+ x86_non_temporal_threshold. */
#ifndef LOG_4X_MEMCPY_THRESH
# define LOG_4X_MEMCPY_THRESH 4
#endif
@@ -724,9 +730,14 @@ L(skip_short_movsb_check):
.p2align 4,, 10
#if (defined USE_MULTIARCH || VEC_SIZE == 16) && IS_IN (libc)
L(large_memcpy_2x_check):
- cmp __x86_rep_movsb_threshold(%rip), %RDX_LP
- jb L(more_8x_vec_check)
+ /* Entry from L(large_memcpy_2x) has a redundant load of
+ __x86_shared_non_temporal_threshold(%rip). L(large_memcpy_2x)
+ is only use for the non-erms memmove which is generally less
+ common. */
L(large_memcpy_2x):
+ mov __x86_shared_non_temporal_threshold(%rip), %R11_LP
+ cmp %R11_LP, %RDX_LP
+ jb L(more_8x_vec_check)
/* To reach this point it is impossible for dst > src and
overlap. Remaining to check is src > dst and overlap. rcx
already contains dst - src. Negate rcx to get src - dst. If
@@ -774,18 +785,21 @@ L(large_memcpy_2x):
/* ecx contains -(dst - src). not ecx will return dst - src - 1
which works for testing aliasing. */
notl %ecx
+ movq %rdx, %r10
testl $(PAGE_SIZE - VEC_SIZE * 8), %ecx
jz L(large_memcpy_4x)
- movq %rdx, %r10
- shrq $LOG_4X_MEMCPY_THRESH, %r10
- cmp __x86_shared_non_temporal_threshold(%rip), %r10
+ /* r11 has __x86_shared_non_temporal_threshold. Shift it left
+ by LOG_4X_MEMCPY_THRESH to get L(large_memcpy_4x) threshold.
+ */
+ shlq $LOG_4X_MEMCPY_THRESH, %r11
+ cmp %r11, %rdx
jae L(large_memcpy_4x)
/* edx will store remainder size for copying tail. */
andl $(PAGE_SIZE * 2 - 1), %edx
/* r10 stores outer loop counter. */
- shrq $((LOG_PAGE_SIZE + 1) - LOG_4X_MEMCPY_THRESH), %r10
+ shrq $(LOG_PAGE_SIZE + 1), %r10
/* Copy 4x VEC at a time from 2 pages. */
.p2align 4
L(loop_large_memcpy_2x_outer):
@@ -850,7 +864,6 @@ L(large_memcpy_2x_end):
.p2align 4
L(large_memcpy_4x):
- movq %rdx, %r10
/* edx will store remainder size for copying tail. */
andl $(PAGE_SIZE * 4 - 1), %edx
/* r10 stores outer loop counter. */
--
2.34.1
next prev parent reply other threads:[~2022-06-15 3:57 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-15 0:25 [PATCH v1 1/3] x86: Fix misordered logic for setting `rep_movsb_stop_threshold` Noah Goldstein
2022-06-15 0:25 ` [PATCH v1 2/3] x86: Cleanup bounds checking in large memcpy case Noah Goldstein
2022-06-15 1:07 ` H.J. Lu
2022-06-15 3:57 ` Noah Goldstein
2022-06-15 3:57 ` Noah Goldstein [this message]
2022-06-15 14:52 ` [PATCH v2] " H.J. Lu
2022-06-15 15:13 ` Noah Goldstein
2022-06-15 15:12 ` [PATCH v3] " Noah Goldstein
2022-06-15 16:48 ` H.J. Lu
2022-06-15 17:44 ` Noah Goldstein
2022-06-15 17:41 ` [PATCH v4 1/2] " Noah Goldstein
2022-06-15 17:41 ` [PATCH v4 2/2] x86: Add bounds `x86_non_temporal_threshold` Noah Goldstein
2022-06-15 18:22 ` H.J. Lu
2022-06-15 18:33 ` Noah Goldstein
2022-06-15 18:32 ` [PATCH v5 " Noah Goldstein
2022-06-15 18:43 ` H.J. Lu
2022-06-15 19:52 ` [PATCH v6 2/3] " Noah Goldstein
2022-06-15 20:27 ` H.J. Lu
2022-06-15 20:35 ` Noah Goldstein
2022-06-15 20:34 ` [PATCH v7 " Noah Goldstein
2022-06-15 20:48 ` H.J. Lu
2022-07-14 2:55 ` Sunil Pandey
2022-06-15 18:22 ` [PATCH v4 1/2] x86: Cleanup bounds checking in large memcpy case H.J. Lu
2022-07-14 2:57 ` Sunil Pandey
2022-06-15 0:25 ` [PATCH v1 3/3] x86: Add sse42 implementation to strcmp's ifunc Noah Goldstein
2022-06-15 1:08 ` H.J. Lu
2022-07-14 2:54 ` Sunil Pandey
2022-06-15 1:02 ` [PATCH v1 1/3] x86: Fix misordered logic for setting `rep_movsb_stop_threshold` H.J. Lu
2022-07-14 2:53 ` Sunil Pandey
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