kernel / pub / scm / linux / kernel / git / minchan / linux / refs/tags/v3.8 / . / arch / tile / lib / spinlock_common.h

/* | |

* 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); | |

} |