benchtests/bench-random-lock.c

   1 /* Benchmark internal libc locking functions used in random.
   2    Copyright (C) 2022-2024 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 #define TEST_MAIN
  20 #define TEST_NAME "random-lock"
  21 #define TEST_FUNCTION test_main
  22 #include <pthread.h>
  23 #include <stdio.h>
  24 #include <stdlib.h>
  25 #include "bench-timing.h"
  26 #include "json-lib.h"
  27
  28 /* Modern cores run 20M iterations in about 1 second.  */
  29 #define NUM_ITERS 50000000
  30
  31
  32 /* Measure the overhead of __libc_lock_lock and __libc_lock_unlock by
  33    calling random ().  */
  34 static void
  35 bench_random_lock (json_ctx_t *json_ctx, size_t iters)
  36 {
  37   timing_t start, stop, total;
  38
  39   srandom (0);
  40
  41   /* Warmup to reduce variations due to frequency scaling.  */
  42   for (int i = 0; i < iters / 4; i++)
  43     (void) random ();
  44
  45   TIMING_NOW (start);
  46
  47   for (int i = 0; i < iters; i++)
  48     (void) random ();
  49
  50   TIMING_NOW (stop);
  51
  52   TIMING_DIFF (total, start, stop);
  53
  54   json_element_double (json_ctx, (double) total / (double) iters);
  55 }
  56
  57 static void *
  58 thread_start (void *p)
  59 {
  60   return p;
  61 }
  62
  63 int
  64 test_main (void)
  65 {
  66   json_ctx_t json_ctx;
  67
  68   json_init (&json_ctx, 0, stdout);
  69
  70   json_document_begin (&json_ctx);
  71
  72   json_attr_string (&json_ctx, "timing_type", TIMING_TYPE);
  73   json_attr_object_begin (&json_ctx, "functions");
  74   json_attr_object_begin (&json_ctx, "random");
  75   json_attr_string (&json_ctx, "bench-variant", "single-threaded");
  76   json_array_begin (&json_ctx, "results");
  77
  78   /* Run benchmark single threaded.  */
  79   bench_random_lock (&json_ctx, NUM_ITERS);
  80
  81   json_array_end (&json_ctx);
  82   json_attr_object_end (&json_ctx);
  83
  84   json_attr_object_begin (&json_ctx, "random");
  85   json_attr_string (&json_ctx, "bench-variant", "multi-threaded");
  86   json_array_begin (&json_ctx, "results");
  87
  88   /* Start a short thread to force SINGLE_THREAD_P == false.  This relies on
  89      the runtime disabling single-threaded optimizations when multiple
  90      threads are used, even after they finish.  */
  91
  92   pthread_t t;
  93   pthread_create (&t, NULL, thread_start, NULL);
  94   pthread_join (t, NULL);
  95
  96   /* Repeat benchmark with single-threaded optimizations disabled.  */
  97   bench_random_lock (&json_ctx, NUM_ITERS);
  98
  99   json_array_end (&json_ctx);
 100   json_attr_object_end (&json_ctx);
 101   json_attr_object_end (&json_ctx);
 102   json_document_end (&json_ctx);
 103   return 0;
 104 }
 105
 106 #include "support/test-driver.c"