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tilegx: add optimized sched_getcpu() using TILE_COORD SPR

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We can discover our x,y coordinate in the core mesh with an
mfspr instruction, multiply y by the core mesh width, and have
the core number without needing to ask the kernel.
This commit is contained in:
Chris Metcalf 2012-10-11 12:15:45 -04:00
parent d394eb742a
commit b8d7c0968c
2 changed files with 91 additions and 0 deletions
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4
ports/ChangeLog.tile
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2012-10-11 Chris Metcalf <cmetcalf@tilera.com>
* sysdeps/unix/sysv/linux/tile/tilegx/sched_getcpu.c: New file.
2012-10-02 Siddhesh Poyarekar <siddhesh@redhat.com>
* sysdeps/unix/sysv/linux/tile/nptl/lowlevellock.h: Fix clone

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ports/sysdeps/unix/sysv/linux/tile/tilegx/sched_getcpu.c Normal file
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/* Copyright (C) 2012 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/>. */
#include <errno.h>
#include <stddef.h>
#include <fcntl.h>
#include <unistd.h>
#include <sched.h>
#include <sysdep.h>
#include <arch/spr_def.h>
/* The count of cores horizontally (X dimension) on the chip. */
static int chip_width;
/* Read the chip "width" from the /sys filesystem. */
static int
initialize_chip_width (void)
{
int w = 0;
int fd;
fd = __open ("/sys/devices/system/cpu/chip_width", O_RDONLY);
if (fd >= 0)
{
char buf[64];
ssize_t n;
int i;
n = __read (fd, buf, sizeof (buf));
__close (fd);
for (i = 0; i < n; ++i)
{
if (buf[i] < '0' || buf[i] > '9')
break;
w = (w * 10) + (buf[i] - '0');
}
}
/* Store a negative value so we don't try again. */
if (w == 0)
w = -1;
/* Using an atomic idempotent write here makes this thread-safe. */
chip_width = w;
return w;
}
int
sched_getcpu (void)
{
unsigned int coord;
int w = chip_width;
if (__builtin_expect (w <= 0, 0))
{
if (w == 0)
w = initialize_chip_width ();
if (w < 0)
{
unsigned int cpu;
int r = INLINE_SYSCALL (getcpu, 3, &cpu, NULL, NULL);
return r == -1 ? r : cpu;
}
}
/* Assign 64-bit value to a 32-bit variable to ensure 32-bit multiply. */
coord = __insn_mfspr (SPR_TILE_COORD);
/* Extract Y coord from bits 7..10 and X coord from bits 18..21. */
return ((coord >> 7) & 0xf) * w + ((coord >> 18) & 0xf);
}