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authorSiddhesh Poyarekar <siddhesh@sourceware.org>2017-10-05 21:49:37 +0530
committerSiddhesh Poyarekar <siddhesh@sourceware.org>2017-10-05 22:20:23 +0530
commit9ec87fd2b11ffce5c27c8eacb9deaa20e2373ff5 (patch)
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parent1e9522c61c7a544d59db32cb7fbbd42e6793d848 (diff)
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benchtests: Memory walking benchmark for memcpy
This benchmark is an attempt to eliminate cache effects from string benchmarks. The benchmark walks both ways through a large memory area and copies different sizes of memory and alignments one at a time instead of looping around in the same memory area. This is a good metric to have alongside the other memcpy benchmarks, especially for larger sizes where the likelihood of the call being done only once is pretty high. * benchtests/bench-memcpy-walk.c: New file. * benchtests/Makefile (string-benchset): Add it.
Diffstat (limited to 'benchtests')
-rw-r--r--benchtests/Makefile3
-rw-r--r--benchtests/bench-memcpy-walk.c127
2 files changed, 129 insertions, 1 deletions
diff --git a/benchtests/Makefile b/benchtests/Makefile
index 3acc39cafa..d086cc671f 100644
--- a/benchtests/Makefile
+++ b/benchtests/Makefile
@@ -37,7 +37,8 @@ string-benchset := bcopy bzero memccpy memchr memcmp memcpy memmem memmove \
strcat strchr strchrnul strcmp strcpy strcspn strlen \
strncasecmp strncat strncmp strncpy strnlen strpbrk strrchr \
strspn strstr strcpy_chk stpcpy_chk memrchr strsep strtok \
- strcoll memcpy-large memcpy-random memmove-large memset-large
+ strcoll memcpy-large memcpy-random memmove-large memset-large \
+ memcpy-walk
# Build and run locale-dependent benchmarks only if we're building natively.
ifeq (no,$(cross-compiling))
diff --git a/benchtests/bench-memcpy-walk.c b/benchtests/bench-memcpy-walk.c
new file mode 100644
index 0000000000..69d467d3fe
--- /dev/null
+++ b/benchtests/bench-memcpy-walk.c
@@ -0,0 +1,127 @@
+/* Measure memcpy function combined throughput for different alignments.
+ Copyright (C) 2017 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
+ <http://www.gnu.org/licenses/>. */
+
+/* This microbenchmark measures the throughput of memcpy for various sizes from
+ 1 byte to 32MiB, doubling every iteration and then misaligning by 0-15
+ bytes. The copies are done from source to destination and then back and the
+ source walks forward across the array and the destination walks backward by
+ one byte each, thus measuring misaligned accesses as well. The idea is to
+ avoid caching effects by copying a different string and far enough from each
+ other, walking in different directions so that we can measure prefetcher
+ efficiency (software or hardware) more closely than with a loop copying the
+ same data over and over, which eventually only gives us L1 cache
+ performance. */
+
+#ifndef MEMCPY_RESULT
+# define MEMCPY_RESULT(dst, len) dst
+# define START_SIZE 1
+# define MIN_PAGE_SIZE (getpagesize () + 32 * 1024 * 1024)
+# define TEST_MAIN
+# define TEST_NAME "memcpy"
+# define TIMEOUT (20 * 60)
+# include "bench-string.h"
+
+IMPL (memcpy, 1)
+#endif
+
+#include "json-lib.h"
+
+typedef char *(*proto_t) (char *, const char *, size_t);
+
+static void
+do_one_test (json_ctx_t *json_ctx, impl_t *impl, char *dst, char *src,
+ size_t len)
+{
+ size_t i, iters = MIN_PAGE_SIZE / len;
+ timing_t start, stop, cur;
+
+ char *dst_end = dst + MIN_PAGE_SIZE - len;
+ char *src_end = src + MIN_PAGE_SIZE - len;
+
+ TIMING_NOW (start);
+ /* Copy the entire buffer back and forth, LEN at a time. */
+ for (i = 0; i < iters && dst_end >= dst && src <= src_end; src++, dst_end--)
+ {
+ CALL (impl, dst_end, src, len);
+ CALL (impl, src, dst_end, len);
+ i += 2;
+ }
+ TIMING_NOW (stop);
+
+ TIMING_DIFF (cur, start, stop);
+
+ /* Get time taken per function call. */
+ json_element_double (json_ctx, (double) cur * len / i);
+}
+
+static void
+do_test (json_ctx_t *json_ctx, size_t len)
+{
+ json_element_object_begin (json_ctx);
+ json_attr_uint (json_ctx, "length", (double) len);
+ json_array_begin (json_ctx, "timings");
+
+ FOR_EACH_IMPL (impl, 0)
+ do_one_test (json_ctx, impl, (char *) buf2, (char *) buf1, len);
+
+ json_array_end (json_ctx);
+ json_element_object_end (json_ctx);
+}
+
+int
+test_main (void)
+{
+ json_ctx_t json_ctx;
+ size_t i;
+
+ test_init ();
+
+ json_init (&json_ctx, 0, stdout);
+
+ json_document_begin (&json_ctx);
+ json_attr_string (&json_ctx, "timing_type", TIMING_TYPE);
+
+ json_attr_object_begin (&json_ctx, "functions");
+ json_attr_object_begin (&json_ctx, "memcpy");
+ json_attr_string (&json_ctx, "bench-variant", "walk");
+
+ json_array_begin (&json_ctx, "ifuncs");
+ FOR_EACH_IMPL (impl, 0)
+ json_element_string (&json_ctx, impl->name);
+ json_array_end (&json_ctx);
+
+ json_array_begin (&json_ctx, "results");
+ for (i = START_SIZE; i <= MIN_PAGE_SIZE; i <<= 1)
+ {
+ /* Test length alignments from 0-16 bytes. */
+ for (int j = 0; j < 8; j++)
+ {
+ do_test (&json_ctx, i + j);
+ do_test (&json_ctx, i + 16 - j);
+ }
+ }
+
+ json_array_end (&json_ctx);
+ json_attr_object_end (&json_ctx);
+ json_attr_object_end (&json_ctx);
+ json_document_end (&json_ctx);
+
+ return ret;
+}
+
+#include <support/test-driver.c>