[PATCH 1/2] benchtests: Memory walking benchmark for memcpy

[Siddhesh Poyarekar <siddhesh at sourceware dot org>]

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.

The benchmark is unlike other string benchmarks in that it prints the
total data rate achieved during a walk across the memory and not the
time taken per execution.

	* benchtests/bench-memcpy-walk.c: New file.
	* benchtests/Makefile (string-benchset): Add it.

---
 benchtests/Makefile            |   3 +-
 benchtests/bench-memcpy-walk.c | 126 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 128 insertions(+), 1 deletion(-)
 create mode 100644 benchtests/bench-memcpy-walk.c

diff --git a/benchtests/Makefile b/benchtests/Makefile
index a0c3470..fbdeadf 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 0000000..df6aa33
--- /dev/null
+++ b/benchtests/bench-memcpy-walk.c
@@ -0,0 +1,126 @@
+/* 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;
+  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 += (len << 1);
+    }
+  TIMING_NOW (stop);
+
+  TIMING_DIFF (cur, start, stop);
+
+  json_element_double (json_ctx, (double) iters / (double) cur);
+}
+
+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", "throughput");
+
+  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>
-- 
2.7.4