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/arch/tile/lib/spinlock_common.h

https://bitbucket.org/ndreys/linux-sunxi
C++ Header | 64 lines | 23 code | 8 blank | 33 comment | 2 complexity | 8b9e5ec1f636a5d86947dcb0341e3b95 MD5 | raw file
Possible License(s): GPL-2.0, LGPL-2.0, AGPL-1.0
 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 */
29static inline void
30relax(int iterations)
31{
32	for (/*above*/; iterations > 0; iterations--)
33		__insn_mfspr(SPR_PASS);
34	barrier();
35}
36
37/* Perform bounded exponential backoff.*/
38static void delay_backoff(int iterations)
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
63	relax(1 << exponent);
64}