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      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 */
    125