benchtests/bench-memcpy-walk.c

   1 /* Measure memcpy function combined throughput for different alignments.
   2    Copyright (C) 2017-2020 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <https://www.gnu.org/licenses/>.  */
  18
  19 /* This microbenchmark measures the throughput of memcpy for various sizes from
  20    1 byte to 32MiB, doubling every iteration and then misaligning by 0-15
  21    bytes.  The copies are done from source to destination and then back and the
  22    source walks forward across the array and the destination walks backward by
  23    one byte each, thus measuring misaligned accesses as well.  The idea is to
  24    avoid caching effects by copying a different string and far enough from each
  25    other, walking in different directions so that we can measure prefetcher
  26    efficiency (software or hardware) more closely than with a loop copying the
  27    same data over and over, which eventually only gives us L1 cache
  28    performance.  */
  29
  30 #ifndef MEMCPY_RESULT
  31 # define MEMCPY_RESULT(dst, len) dst
  32 # define START_SIZE 128
  33 # define MIN_PAGE_SIZE (getpagesize () + 32 * 1024 * 1024)
  34 # define TEST_MAIN
  35 # define TEST_NAME "memcpy"
  36 # define TIMEOUT (20 * 60)
  37 # include "bench-string.h"
  38
  39 IMPL (memcpy, 1)
  40 #endif
  41
  42 #include "json-lib.h"
  43
  44 typedef char *(*proto_t) (char *, const char *, size_t);
  45
  46 static void
  47 do_one_test (json_ctx_t *json_ctx, impl_t *impl, char *dst, char *src,
  48              size_t len)
  49 {
  50   size_t i = 0;
  51   timing_t start, stop, cur;
  52
  53   char *dst_end = dst + MIN_PAGE_SIZE - len;
  54   char *src_end = src + MIN_PAGE_SIZE - len;
  55
  56   TIMING_NOW (start);
  57   /* Copy the entire buffer backwards, LEN at a time.  */
  58   for (; src_end >= src && dst_end >= dst; src_end -= len, dst_end -= len, i++)
  59     CALL (impl, src_end, dst_end, len);
  60   TIMING_NOW (stop);
  61
  62   TIMING_DIFF (cur, start, stop);
  63
  64   /* Get time taken per function call.  */
  65   json_element_double (json_ctx, (double) cur / i);
  66 }
  67
  68 static void
  69 do_test (json_ctx_t *json_ctx, size_t len)
  70 {
  71   json_element_object_begin (json_ctx);
  72   json_attr_uint (json_ctx, "length", (double) len);
  73   json_array_begin (json_ctx, "timings");
  74
  75   FOR_EACH_IMPL (impl, 0)
  76     do_one_test (json_ctx, impl, (char *) buf2, (char *) buf1, len);
  77
  78   json_array_end (json_ctx);
  79   json_element_object_end (json_ctx);
  80 }
  81
  82 int
  83 test_main (void)
  84 {
  85   json_ctx_t json_ctx;
  86
  87   test_init ();
  88
  89   json_init (&json_ctx, 0, stdout);
  90
  91   json_document_begin (&json_ctx);
  92   json_attr_string (&json_ctx, "timing_type", TIMING_TYPE);
  93
  94   json_attr_object_begin (&json_ctx, "functions");
  95   json_attr_object_begin (&json_ctx, "memcpy");
  96   json_attr_string (&json_ctx, "bench-variant", "walk");
  97
  98   json_array_begin (&json_ctx, "ifuncs");
  99   FOR_EACH_IMPL (impl, 0)
 100     json_element_string (&json_ctx, impl->name);
 101   json_array_end (&json_ctx);
 102
 103   json_array_begin (&json_ctx, "results");
 104   for (size_t i = START_SIZE; i <= MIN_PAGE_SIZE; i <<= 1)
 105     {
 106       do_test (&json_ctx, i);
 107       do_test (&json_ctx, i + 1);
 108     }
 109
 110   json_array_end (&json_ctx);
 111   json_attr_object_end (&json_ctx);
 112   json_attr_object_end (&json_ctx);
 113   json_document_end (&json_ctx);
 114
 115   return ret;
 116 }
 117
 118 #include <support/test-driver.c>