1 /*
2 * CDDL HEADER START
3 *
4 * The contents of this file are subject to the terms of the
5 * Common Development and Distribution License (the "License").
6 * You may not use this file except in compliance with the License.
7 *
8 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
9 * or http://www.opensolaris.org/os/licensing.
10 * See the License for the specific language governing permissions
11 * and limitations under the License.
12 *
13 * When distributing Covered Code, include this CDDL HEADER in each
14 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
15 * If applicable, add the following below this CDDL HEADER, with the
16 * fields enclosed by brackets "[]" replaced with your own identifying
17 * information: Portions Copyright [yyyy] [name of copyright owner]
18 *
19 * CDDL HEADER END
20 */
21
22 /*
23 * Copyright 2009 Sun Microsystems, Inc. All rights reserved.
24 * Use is subject to license terms.
25 */
26
27 /*
28 * Copyright (c) 2013 by Delphix. All rights reserved.
29 */
30
31 #ifndef _SYS_TXG_IMPL_H
32 #define _SYS_TXG_IMPL_H
33
34 #include <sys/spa.h>
35 #include <sys/txg.h>
36
37 #ifdef __cplusplus
38 extern "C" {
39 #endif
40
41 /*
42 * The tx_cpu structure is a per-cpu structure that is used to track
43 * the number of active transaction holds (tc_count). As transactions
44 * are assigned into a transaction group the appropriate tc_count is
45 * incremented to indicate that there are pending changes that have yet
46 * to quiesce. Consumers evenutally call txg_rele_to_sync() to decrement
47 * the tc_count. A transaction group is not considered quiesced until all
48 * tx_cpu structures have reached a tc_count of zero.
49 *
50 * This structure is a per-cpu structure by design. Updates to this structure
51 * are frequent and concurrent. Having a single structure would result in
52 * heavy lock contention so a per-cpu design was implemented. With the fanned
53 * out mutex design, consumers only need to lock the mutex associated with
54 * thread's cpu.
55 *
56 * The tx_cpu contains two locks, the tc_lock and tc_open_lock.
57 * The tc_lock is used to protect all members of the tx_cpu structure with
58 * the exception of the tc_open_lock. This lock should only be held for a
59 * short period of time, typically when updating the value of tc_count.
60 *
61 * The tc_open_lock protects the tx_open_txg member of the tx_state structure.
62 * This lock is used to ensure that transactions are only assigned into
63 * the current open transaction group. In order to move the current open
64 * transaction group to the quiesce phase, the txg_quiesce thread must
65 * grab all tc_open_locks, increment the tx_open_txg, and drop the locks.
66 * The tc_open_lock is held until the transaction is assigned into the
67 * transaction group. Typically, this is a short operation but if throttling
68 * is occuring it may be held for longer periods of time.
69 */
70 struct tx_cpu {
71 kmutex_t tc_open_lock; /* protects tx_open_txg */
72 kmutex_t tc_lock; /* protects the rest of this struct */
73 kcondvar_t tc_cv[TXG_SIZE];
74 uint64_t tc_count[TXG_SIZE]; /* tx hold count on each txg */
75 list_t tc_callbacks[TXG_SIZE]; /* commit cb list */
76 char tc_pad[8]; /* pad to fill 3 cache lines */
77 };
78
79 /*
80 * The tx_state structure maintains the state information about the different
81 * stages of the pool's transcation groups. A per pool tx_state structure
82 * is used to track this information. The tx_state structure also points to
83 * an array of tx_cpu structures (described above). Although the tx_sync_lock
84 * is used to protect the members of this structure, it is not used to
85 * protect the tx_open_txg. Instead a special lock in the tx_cpu structure
86 * is used. Readers of tx_open_txg must grab the per-cpu tc_open_lock.
87 * Any thread wishing to update tx_open_txg must grab the tc_open_lock on
88 * every cpu (see txg_quiesce()).
89 */
90 typedef struct tx_state {
91 tx_cpu_t *tx_cpu; /* protects access to tx_open_txg */
92 kmutex_t tx_sync_lock; /* protects the rest of this struct */
93
94 uint64_t tx_open_txg; /* currently open txg id */
95 uint64_t tx_quiesced_txg; /* quiesced txg waiting for sync */
96 uint64_t tx_syncing_txg; /* currently syncing txg id */
97 uint64_t tx_synced_txg; /* last synced txg id */
98
99 hrtime_t tx_open_time; /* start time of tx_open_txg */
100
101 uint64_t tx_sync_txg_waiting; /* txg we're waiting to sync */
102 uint64_t tx_quiesce_txg_waiting; /* txg we're waiting to open */
103
104 kcondvar_t tx_sync_more_cv;
105 kcondvar_t tx_sync_done_cv;
106 kcondvar_t tx_quiesce_more_cv;
107 kcondvar_t tx_quiesce_done_cv;
108 kcondvar_t tx_timeout_cv;
109 kcondvar_t tx_exit_cv; /* wait for all threads to exit */
110
111 uint8_t tx_threads; /* number of threads */
112 uint8_t tx_exiting; /* set when we're exiting */
113
114 kthread_t *tx_sync_thread;
115 kthread_t *tx_quiesce_thread;
116
117 taskq_t *tx_commit_cb_taskq; /* commit callback taskq */
118 } tx_state_t;
119
120 #ifdef __cplusplus
121 }
122 #endif
123
124 #endif /* _SYS_TXG_IMPL_H */