benchtests: Memory walking benchmark for memset

This benchmark is an attempt to eliminate cache effects from string
benchmarks.  The benchmark walks backward through a large memory area
and sets 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 memset 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.

	* benchtests/bench-memset-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-memset-walk.c: New file.
+	* benchtests/Makefile (string-benchset): Add it.
+
 	* benchtests/bench-memcpy-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
+		   memcpy-walk memset-walk
 
 # Build and run locale-dependent benchmarks only if we're building natively.
 ifeq (no,$(cross-compiling))

benchtests/bench-memset-walk.c

@@ -0,0 +1,138 @@
+/* Measure memset function throughput with large data sizes.
+   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/>.  */
+
+#define TEST_MAIN
+#ifndef WIDE
+# define TEST_NAME "memset"
+#else
+# define TEST_NAME "wmemset"
+#endif /* WIDE */
+#define START_SIZE (1)
+#define MIN_PAGE_SIZE (getpagesize () + 32 * 1024 * 1024)
+#define TIMEOUT (20 * 60)
+#include "bench-string.h"
+
+#ifndef WIDE
+# define MEMSET memset
+# define CHAR char
+# define SIMPLE_MEMSET simple_memset
+# define MEMCMP memcmp
+#else
+# include <wchar.h>
+# define MEMSET wmemset
+# define CHAR wchar_t
+# define SIMPLE_MEMSET simple_wmemset
+# define MEMCMP wmemcmp
+#endif /* WIDE */
+
+#include <assert.h>
+#include "json-lib.h"
+
+
+typedef CHAR *(*proto_t) (CHAR *, int, size_t);
+
+CHAR *
+inhibit_loop_to_libcall
+SIMPLE_MEMSET (CHAR *s, int c, size_t n)
+{
+  CHAR *r = s, *end = s + n;
+  while (r < end)
+    *r++ = c;
+  return s;
+}
+
+IMPL (SIMPLE_MEMSET, 1)
+
+static void
+do_one_test (json_ctx_t *json_ctx, impl_t *impl, CHAR *s, CHAR *s_end,
+	     int c __attribute ((unused)), size_t n)
+{
+  size_t i, iters = MIN_PAGE_SIZE / n;
+  timing_t start, stop, cur;
+
+  TIMING_NOW (start);
+  for (i = 0; i < iters && s <= s_end; s++, i++)
+    CALL (impl, s, c, n);
+  TIMING_NOW (stop);
+
+  TIMING_DIFF (cur, start, stop);
+
+  /* Get time taken per function call.  */
+  json_element_double (json_ctx, (double) cur * n / i);
+}
+
+static void
+do_test (json_ctx_t *json_ctx, int c, size_t len)
+{
+  json_element_object_begin (json_ctx);
+  json_attr_uint (json_ctx, "length", len);
+  json_attr_uint (json_ctx, "char", c);
+  json_array_begin (json_ctx, "timings");
+
+  FOR_EACH_IMPL (impl, 0)
+    {
+      do_one_test (json_ctx, impl, (CHAR *) buf1,
+		   (CHAR *) buf1 + MIN_PAGE_SIZE - len, c, len);
+      realloc_bufs ();
+    }
+
+  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, TEST_NAME);
+  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 < i && j < 16; j++)
+	do_test (&json_ctx, 65, i + j);
+
+  for (i = START_SIZE; i <= MIN_PAGE_SIZE; i <<= 1)
+      for (int j = 0; j < i && j < 16; j++)
+	do_test (&json_ctx, 0, i + 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>