[PATCH v3] malloc: Optimize small memory zeroing for calloc
H.J. Lu
hjl.tools@gmail.com
Thu Nov 28 09:56:34 GMT 2024
For memory size up to 9 * INTERNAL_SIZE_T bytes, calloc has special codes
to clear the memory. Add calloc-clear-memory.h to allow architecture
specific optimization. The default unroll size is 9. Since the size
isn't fixed, compiler can't generate the best inline codes for all
targets. Since x86-64 has fast unaligned 16-byte vector stores, arrange
the codes to help compiler vectorize stores with overlapping unaligned
vector stores with 1 branch, instead of up to 3, and up to 5 stores,
instead of 9. The calloc microbenchmark shows:
Test Platform: Xeon-8380
Bench Function: calloc
Ratio: New / Original time_per_iteration (Lower is Better)
Threads# | Ratio
-----------|------
1 thread | 0.953
4 threads | 0.952
NB: Since INTERNAL_SIZE_T can be either 4 bytes or 8 bytes and not all
targets have fast unaligned vector stores, x86-64 approach doesn't work
for all targets.
Signed-off-by: H.J. Lu <hjl.tools@gmail.com>
---
malloc/malloc-internal.h | 1 +
malloc/malloc.c | 30 +++-------------
sysdeps/generic/calloc-clear-memory.h | 46 +++++++++++++++++++++++++
sysdeps/x86_64/64/calloc-clear-memory.h | 44 +++++++++++++++++++++++
4 files changed, 96 insertions(+), 25 deletions(-)
create mode 100644 sysdeps/generic/calloc-clear-memory.h
create mode 100644 sysdeps/x86_64/64/calloc-clear-memory.h
diff --git a/malloc/malloc-internal.h b/malloc/malloc-internal.h
index cba03433fe..3349e2d1fe 100644
--- a/malloc/malloc-internal.h
+++ b/malloc/malloc-internal.h
@@ -23,6 +23,7 @@
#include <malloc-sysdep.h>
#include <malloc-size.h>
#include <malloc-hugepages.h>
+#include <calloc-clear-memory.h>
/* Called in the parent process before a fork. */
void __malloc_fork_lock_parent (void) attribute_hidden;
diff --git a/malloc/malloc.c b/malloc/malloc.c
index 81ddd2c3a8..53f5c856ad 100644
--- a/malloc/malloc.c
+++ b/malloc/malloc.c
@@ -3853,38 +3853,18 @@ __libc_calloc (size_t n, size_t elem_size)
}
#endif
- /* Unroll clear of <= 36 bytes (72 if 8byte sizes). We know that
- contents have an odd number of INTERNAL_SIZE_T-sized words;
- minimally 3. */
+ /* Unroll clear of <= MAX_CLEAR_SMALL_MEMORY_SIZE * INTERNAL_SIZE_T
+ bytes. We know that contents have an odd number of INTERNAL_SIZE_T-
+ sized words; minimally 3. */
d = (INTERNAL_SIZE_T *) mem;
clearsize = csz - SIZE_SZ;
nclears = clearsize / sizeof (INTERNAL_SIZE_T);
assert (nclears >= 3);
- if (nclears > 9)
+ if (nclears > MAX_CLEAR_SMALL_MEMORY_SIZE)
return memset (d, 0, clearsize);
-
else
- {
- *(d + 0) = 0;
- *(d + 1) = 0;
- *(d + 2) = 0;
- if (nclears > 4)
- {
- *(d + 3) = 0;
- *(d + 4) = 0;
- if (nclears > 6)
- {
- *(d + 5) = 0;
- *(d + 6) = 0;
- if (nclears > 8)
- {
- *(d + 7) = 0;
- *(d + 8) = 0;
- }
- }
- }
- }
+ clear_small_memory (d, nclears);
return mem;
}
diff --git a/sysdeps/generic/calloc-clear-memory.h b/sysdeps/generic/calloc-clear-memory.h
new file mode 100644
index 0000000000..2b9a2941dc
--- /dev/null
+++ b/sysdeps/generic/calloc-clear-memory.h
@@ -0,0 +1,46 @@
+/* Clear a block of memory for calloc. Generic version.
+ Copyright (C) 2024 Free Software Foundation, Inc.
+ This file is part of the GNU C Library.
+
+ The GNU C Library is free software; you can redistribute it and/or
+ modify it under the terms of the GNU Lesser General Public
+ License as published by the Free Software Foundation; either
+ version 2.1 of the License, or (at your option) any later version.
+
+ The GNU C Library 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
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with the GNU C Library; if not, see
+ <https://www.gnu.org/licenses/>. */
+
+#define MAX_CLEAR_SMALL_MEMORY_SIZE 9
+
+/* Clear a memory size up to MAX_CLEAR_SMALL_MEMORY_SIZE * INTERNAL_SIZE_T
+ bytes. We know that contents have an odd number of INTERNAL_SIZE_T-
+ sized words; minimally 3 words. */
+
+static __always_inline void
+clear_small_memory (INTERNAL_SIZE_T *mem, unsigned long nclears)
+{
+ *(mem + 0) = 0;
+ *(mem + 1) = 0;
+ *(mem + 2) = 0;
+ if (nclears > 4)
+ {
+ *(mem + 3) = 0;
+ *(mem + 4) = 0;
+ if (nclears > 6)
+ {
+ *(mem + 5) = 0;
+ *(mem + 6) = 0;
+ if (nclears > 8)
+ {
+ *(mem + 7) = 0;
+ *(mem + 8) = 0;
+ }
+ }
+ }
+}
diff --git a/sysdeps/x86_64/64/calloc-clear-memory.h b/sysdeps/x86_64/64/calloc-clear-memory.h
new file mode 100644
index 0000000000..b9fbd896d0
--- /dev/null
+++ b/sysdeps/x86_64/64/calloc-clear-memory.h
@@ -0,0 +1,44 @@
+/* Clear a block of memory for calloc. X86-64/LP64 version.
+ Copyright (C) 2024 Free Software Foundation, Inc.
+ This file is part of the GNU C Library.
+
+ The GNU C Library is free software; you can redistribute it and/or
+ modify it under the terms of the GNU Lesser General Public
+ License as published by the Free Software Foundation; either
+ version 2.1 of the License, or (at your option) any later version.
+
+ The GNU C Library 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
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with the GNU C Library; if not, see
+ <https://www.gnu.org/licenses/>. */
+
+#define MAX_CLEAR_SMALL_MEMORY_SIZE 9
+
+/* Clear a memory size up to MAX_CLEAR_SMALL_MEMORY_SIZE * INTERNAL_SIZE_T
+ bytes. We know that contents have an odd number of INTERNAL_SIZE_T-
+ sized words; minimally 3 words. */
+
+static __always_inline void
+clear_small_memory (INTERNAL_SIZE_T *mem, unsigned long nclears)
+{
+ /* Since x86-64 has fast unaligned 16-byte vector stores, arrange the
+ codes to help compiler vectorize stores with overlapping unaligned
+ vector stores with 1 branch, instead of up to 3, and up to 5 stores,
+ instead of 9. */
+ *(mem + 0) = 0;
+ *(mem + 1) = 0;
+ *(mem + 2) = 0;
+ *(mem + nclears - 2) = 0;
+ *(mem + nclears - 2 + 1) = 0;
+ if (nclears > 6)
+ {
+ *(mem + 3) = 0;
+ *(mem + 3 + 1) = 0;
+ *(mem + nclears - 4) = 0;
+ *(mem + nclears - 4 + 1) = 0;
+ }
+}
--
2.47.0
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