sysdeps/unix/sysv/linux/tile/sched_getcpu.c

   1 /* Copyright (C) 2012-2018 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3
   4    The GNU C Library is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU Lesser General Public
   6    License as published by the Free Software Foundation; either
   7    version 2.1 of the License, or (at your option) any later version.
   8
   9    The GNU C Library is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12    Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public
  15    License along with the GNU C Library.  If not, see
  16    <http://www.gnu.org/licenses/>.  */
  17
  18 #include <errno.h>
  19 #include <stddef.h>
  20 #include <fcntl.h>
  21 #include <unistd.h>
  22 #include <sched.h>
  23 #include <sysdep.h>
  24 #include <arch/spr_def.h>
  25
  26
  27 /* The count of cores horizontally (X dimension) on the chip.  */
  28 static int chip_width;
  29
  30 /* Read the chip "width" from the /sys filesystem.  */
  31 static int
  32 initialize_chip_width (void)
  33 {
  34   int w = 0;
  35   int fd;
  36
  37   fd = __open ("/sys/devices/system/cpu/chip_width", O_RDONLY);
  38   if (fd >= 0)
  39     {
  40       char buf[64];
  41       ssize_t n;
  42       int i;
  43
  44       n = __read (fd, buf, sizeof (buf));
  45       __close (fd);
  46
  47       for (i = 0; i < n; ++i)
  48         {
  49           if (buf[i] < '0' || buf[i] > '9')
  50             break;
  51           w = (w * 10) + (buf[i] - '0');
  52         }
  53     }
  54
  55   /* Store a negative value so we don't try again.  */
  56   if (w == 0)
  57     w = -1;
  58
  59   /* Using an atomic idempotent write here makes this thread-safe.  */
  60   chip_width = w;
  61   return w;
  62 }
  63
  64 int
  65 sched_getcpu (void)
  66 {
  67   unsigned int coord;
  68   int w = chip_width;
  69
  70   if (__builtin_expect (w <= 0, 0))
  71     {
  72       if (w == 0)
  73         w = initialize_chip_width ();
  74       if (w < 0)
  75         {
  76           unsigned int cpu;
  77           int r = INLINE_SYSCALL (getcpu, 3, &cpu, NULL, NULL);
  78           return r == -1 ? r : cpu;
  79         }
  80     }
  81
  82   /* Assign 64-bit value to a 32-bit variable to ensure 32-bit multiply.  */
  83   coord = __insn_mfspr (SPR_TILE_COORD);
  84
  85   /* Extract Y coord from bits 7..10 and X coord from bits 18..21.  */
  86   return ((coord >> 7) & 0xf) * w + ((coord >> 18) & 0xf);
  87 }