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867e359b CM |
1 | /* |
2 | * Copyright 2010 Tilera Corporation. All Rights Reserved. | |
3 | * | |
4 | * This program is free software; you can redistribute it and/or | |
5 | * modify it under the terms of the GNU General Public License | |
6 | * as published by the Free Software Foundation, version 2. | |
7 | * | |
8 | * This program is distributed in the hope that it will be useful, but | |
9 | * WITHOUT ANY WARRANTY; without even the implied warranty of | |
10 | * MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or | |
11 | * NON INFRINGEMENT. See the GNU General Public License for | |
12 | * more details. | |
13 | * This file is included into spinlock_32.c or _64.c. | |
14 | */ | |
15 | ||
16 | /* | |
17 | * The mfspr in __spinlock_relax() is 5 or 6 cycles plus 2 for loop | |
18 | * overhead. | |
19 | */ | |
20 | #ifdef __tilegx__ | |
21 | #define CYCLES_PER_RELAX_LOOP 7 | |
22 | #else | |
23 | #define CYCLES_PER_RELAX_LOOP 8 | |
24 | #endif | |
25 | ||
26 | /* | |
27 | * Idle the core for CYCLES_PER_RELAX_LOOP * iterations cycles. | |
28 | */ | |
29 | static inline void | |
30 | relax(int iterations) | |
31 | { | |
32 | for (/*above*/; iterations > 0; iterations--) | |
33 | __insn_mfspr(SPR_PASS); | |
34 | barrier(); | |
35 | } | |
36 | ||
37 | /* Perform bounded exponential backoff.*/ | |
0707ad30 | 38 | static void delay_backoff(int iterations) |
867e359b CM |
39 | { |
40 | u32 exponent, loops; | |
41 | ||
42 | /* | |
43 | * 2^exponent is how many times we go around the loop, | |
44 | * which takes 8 cycles. We want to start with a 16- to 31-cycle | |
45 | * loop, so we need to go around minimum 2 = 2^1 times, so we | |
46 | * bias the original value up by 1. | |
47 | */ | |
48 | exponent = iterations + 1; | |
49 | ||
50 | /* | |
51 | * Don't allow exponent to exceed 7, so we have 128 loops, | |
52 | * or 1,024 (to 2,047) cycles, as our maximum. | |
53 | */ | |
54 | if (exponent > 8) | |
55 | exponent = 8; | |
56 | ||
57 | loops = 1 << exponent; | |
58 | ||
59 | /* Add a randomness factor so two cpus never get in lock step. */ | |
60 | loops += __insn_crc32_32(stack_pointer, get_cycles_low()) & | |
61 | (loops - 1); | |
62 | ||
444eef1b | 63 | relax(loops); |
867e359b | 64 | } |