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authorChris Metcalf <cmetcalf@tilera.com>2012-10-11 12:15:45 -0400
committerChris Metcalf <cmetcalf@tilera.com>2012-10-12 14:26:25 -0400
commitb8d7c0968c095d25fded0e2dfea1a16b1fd42911 (patch)
tree23fcb29c3e941adaeece6e4375deedcecd7e305a /ports
parentd394eb742a3565d7fe7a4b02710a60b5f219ee64 (diff)
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tilegx: add optimized sched_getcpu() using TILE_COORD SPR
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.
Diffstat (limited to 'ports')
-rw-r--r--ports/ChangeLog.tile4
-rw-r--r--ports/sysdeps/unix/sysv/linux/tile/tilegx/sched_getcpu.c87
2 files changed, 91 insertions, 0 deletions
diff --git a/ports/ChangeLog.tile b/ports/ChangeLog.tile
index 2d19358e75..dfe5e9c60f 100644
--- a/ports/ChangeLog.tile
+++ b/ports/ChangeLog.tile
@@ -1,3 +1,7 @@
+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
diff --git a/ports/sysdeps/unix/sysv/linux/tile/tilegx/sched_getcpu.c b/ports/sysdeps/unix/sysv/linux/tile/tilegx/sched_getcpu.c
new file mode 100644
index 0000000000..e9c5bd282e
--- /dev/null
+++ b/ports/sysdeps/unix/sysv/linux/tile/tilegx/sched_getcpu.c
@@ -0,0 +1,87 @@
+/* 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);
+}