benchtests: Memory walking benchmark for memmove

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 simple memmove benchmark (which is only
really useful for smaller sizes) especially for larger sizes where the
likelihood of the call being done only once is pretty high.

This benchmark is different from memcpy in that it also tests
overlapping copies.

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

ChangeLog

@@ -1,5 +1,8 @@
 2017-10-05  Siddhesh Poyarekar  <siddhesh@sourceware.org>
 
+	* benchtests/bench-memmove-walk.c: New file.
+	* benchtests/Makefile (string-benchset): Add it.
+
 	* benchtests/bench-memset-walk.c: New file.
 	* benchtests/Makefile (string-benchset): Add it.
 

benchtests/Makefile

@@ -38,7 +38,7 @@ string-benchset := bcopy bzero memccpy memchr memcmp memcpy memmem memmove \
 		   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 \
-		   memcpy-walk memset-walk
+		   memcpy-walk memset-walk memmove-walk
 
 # Build and run locale-dependent benchmarks only if we're building natively.
 ifeq (no,$(cross-compiling))

benchtests/bench-memmove-walk.c

@@ -0,0 +1,143 @@
+/* Measure memmove 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 memmove 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 MEMMOVE_RESULT
+# define MEMMOVE_RESULT(dst, len) dst
+# define START_SIZE 1
+# define MIN_PAGE_SIZE (getpagesize () + 32 * 1024 * 1024)
+# define TEST_MAIN
+# define TEST_NAME "memmove"
+# define TIMEOUT (20 * 60)
+# include "bench-string.h"
+
+IMPL (memmove, 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, bool overlap)
+{
+  json_element_object_begin (json_ctx);
+  json_attr_uint (json_ctx, "length", (double) len);
+  json_array_begin (json_ctx, "timings");
+
+  if (overlap)
+    buf2 = buf1;
+
+  /* First the non-overlapping moves.  */
+  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, "memmove");
+  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");
+  /* Non-overlapping buffers.  */
+  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, false);
+	  do_test (&json_ctx, i + 16 - j, false);
+	}
+    }
+
+  /* Overlapping buffers.  */
+  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, true);
+	  do_test (&json_ctx, i + 16 - j, true);
+	}
+    }
+
+  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>