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-rw-r--r--arch/tile/lib/spinlock_common.h64
1 files changed, 64 insertions, 0 deletions
diff --git a/arch/tile/lib/spinlock_common.h b/arch/tile/lib/spinlock_common.h
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+++ b/arch/tile/lib/spinlock_common.h
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+/*
+ * Copyright 2010 Tilera Corporation. All Rights Reserved.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation, version 2.
+ *
+ * This program 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, GOOD TITLE or
+ * NON INFRINGEMENT. See the GNU General Public License for
+ * more details.
+ * This file is included into spinlock_32.c or _64.c.
+ */
+
+/*
+ * The mfspr in __spinlock_relax() is 5 or 6 cycles plus 2 for loop
+ * overhead.
+ */
+#ifdef __tilegx__
+#define CYCLES_PER_RELAX_LOOP 7
+#else
+#define CYCLES_PER_RELAX_LOOP 8
+#endif
+
+/*
+ * Idle the core for CYCLES_PER_RELAX_LOOP * iterations cycles.
+ */
+static inline void
+relax(int iterations)
+{
+ for (/*above*/; iterations > 0; iterations--)
+ __insn_mfspr(SPR_PASS);
+ barrier();
+}
+
+/* Perform bounded exponential backoff.*/
+static void delay_backoff(int iterations)
+{
+ u32 exponent, loops;
+
+ /*
+ * 2^exponent is how many times we go around the loop,
+ * which takes 8 cycles. We want to start with a 16- to 31-cycle
+ * loop, so we need to go around minimum 2 = 2^1 times, so we
+ * bias the original value up by 1.
+ */
+ exponent = iterations + 1;
+
+ /*
+ * Don't allow exponent to exceed 7, so we have 128 loops,
+ * or 1,024 (to 2,047) cycles, as our maximum.
+ */
+ if (exponent > 8)
+ exponent = 8;
+
+ loops = 1 << exponent;
+
+ /* Add a randomness factor so two cpus never get in lock step. */
+ loops += __insn_crc32_32(stack_pointer, get_cycles_low()) &
+ (loops - 1);
+
+ relax(loops);
+}