blob: 6ac37509faca56ab614eae690123bf9be9be9313 [file] [log] [blame]
 /* * 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); }