xref: /freebsd/sys/contrib/ck/include/ck_backoff.h (revision 61e21613)
1 /*
2  * Copyright 2009-2015 Samy Al Bahra.
3  * All rights reserved.
4  *
5  * Redistribution and use in source and binary forms, with or without
6  * modification, are permitted provided that the following conditions
7  * are met:
8  * 1. Redistributions of source code must retain the above copyright
9  *    notice, this list of conditions and the following disclaimer.
10  * 2. Redistributions in binary form must reproduce the above copyright
11  *    notice, this list of conditions and the following disclaimer in the
12  *    documentation and/or other materials provided with the distribution.
13  *
14  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
15  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
16  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
17  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
18  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
19  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
20  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
21  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
22  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
23  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
24  * SUCH DAMAGE.
25  */
26 
27 #ifndef CK_BACKOFF_H
28 #define CK_BACKOFF_H
29 
30 #include <ck_cc.h>
31 #include <ck_pr.h>
32 
33 #ifndef CK_BACKOFF_CEILING
34 #define CK_BACKOFF_CEILING ((1 << 20) - 1)
35 #endif
36 
37 #define CK_BACKOFF_INITIALIZER (1 << 9)
38 
39 typedef unsigned int ck_backoff_t;
40 
41 /*
42  * This is a exponential back-off implementation.
43  */
44 CK_CC_INLINE static void
45 ck_backoff_eb(unsigned int *c)
46 {
47 	unsigned int i, ceiling;
48 
49 	ceiling = *c;
50 	for (i = 0; i < ceiling; i++)
51 		ck_pr_barrier();
52 
53 	*c = ceiling << (ceiling < CK_BACKOFF_CEILING);
54 	return;
55 }
56 
57 #endif /* CK_BACKOFF_H */
58