diff options
Diffstat (limited to 'sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dmu_tx.c')
| -rw-r--r-- | sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dmu_tx.c | 218 |
1 files changed, 209 insertions, 9 deletions
diff --git a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dmu_tx.c b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dmu_tx.c index 16ee5cf..1213d91 100644 --- a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dmu_tx.c +++ b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/dmu_tx.c @@ -54,6 +54,7 @@ dmu_tx_create_dd(dsl_dir_t *dd) offsetof(dmu_tx_hold_t, txh_node)); list_create(&tx->tx_callbacks, sizeof (dmu_tx_callback_t), offsetof(dmu_tx_callback_t, dcb_node)); + tx->tx_start = gethrtime(); #ifdef ZFS_DEBUG refcount_create(&tx->tx_space_written); refcount_create(&tx->tx_space_freed); @@ -597,13 +598,13 @@ dmu_tx_hold_free(dmu_tx_t *tx, uint64_t object, uint64_t off, uint64_t len) if (txh == NULL) return; dn = txh->txh_dnode; + dmu_tx_count_dnode(txh); if (off >= (dn->dn_maxblkid+1) * dn->dn_datablksz) return; if (len == DMU_OBJECT_END) len = (dn->dn_maxblkid+1) * dn->dn_datablksz - off; - dmu_tx_count_dnode(txh); /* * For i/o error checking, we read the first and last level-0 @@ -918,6 +919,161 @@ dmu_tx_dirty_buf(dmu_tx_t *tx, dmu_buf_impl_t *db) } #endif +/* + * If we can't do 10 iops, something is wrong. Let us go ahead + * and hit zfs_dirty_data_max. + */ +hrtime_t zfs_delay_max_ns = MSEC2NSEC(100); +int zfs_delay_resolution_ns = 100 * 1000; /* 100 microseconds */ + +/* + * We delay transactions when we've determined that the backend storage + * isn't able to accommodate the rate of incoming writes. + * + * If there is already a transaction waiting, we delay relative to when + * that transaction finishes waiting. This way the calculated min_time + * is independent of the number of threads concurrently executing + * transactions. + * + * If we are the only waiter, wait relative to when the transaction + * started, rather than the current time. This credits the transaction for + * "time already served", e.g. reading indirect blocks. + * + * The minimum time for a transaction to take is calculated as: + * min_time = scale * (dirty - min) / (max - dirty) + * min_time is then capped at zfs_delay_max_ns. + * + * The delay has two degrees of freedom that can be adjusted via tunables. + * The percentage of dirty data at which we start to delay is defined by + * zfs_delay_min_dirty_percent. This should typically be at or above + * zfs_vdev_async_write_active_max_dirty_percent so that we only start to + * delay after writing at full speed has failed to keep up with the incoming + * write rate. The scale of the curve is defined by zfs_delay_scale. Roughly + * speaking, this variable determines the amount of delay at the midpoint of + * the curve. + * + * delay + * 10ms +-------------------------------------------------------------*+ + * | *| + * 9ms + *+ + * | *| + * 8ms + *+ + * | * | + * 7ms + * + + * | * | + * 6ms + * + + * | * | + * 5ms + * + + * | * | + * 4ms + * + + * | * | + * 3ms + * + + * | * | + * 2ms + (midpoint) * + + * | | ** | + * 1ms + v *** + + * | zfs_delay_scale ----------> ******** | + * 0 +-------------------------------------*********----------------+ + * 0% <- zfs_dirty_data_max -> 100% + * + * Note that since the delay is added to the outstanding time remaining on the + * most recent transaction, the delay is effectively the inverse of IOPS. + * Here the midpoint of 500us translates to 2000 IOPS. The shape of the curve + * was chosen such that small changes in the amount of accumulated dirty data + * in the first 3/4 of the curve yield relatively small differences in the + * amount of delay. + * + * The effects can be easier to understand when the amount of delay is + * represented on a log scale: + * + * delay + * 100ms +-------------------------------------------------------------++ + * + + + * | | + * + *+ + * 10ms + *+ + * + ** + + * | (midpoint) ** | + * + | ** + + * 1ms + v **** + + * + zfs_delay_scale ----------> ***** + + * | **** | + * + **** + + * 100us + ** + + * + * + + * | * | + * + * + + * 10us + * + + * + + + * | | + * + + + * +--------------------------------------------------------------+ + * 0% <- zfs_dirty_data_max -> 100% + * + * Note here that only as the amount of dirty data approaches its limit does + * the delay start to increase rapidly. The goal of a properly tuned system + * should be to keep the amount of dirty data out of that range by first + * ensuring that the appropriate limits are set for the I/O scheduler to reach + * optimal throughput on the backend storage, and then by changing the value + * of zfs_delay_scale to increase the steepness of the curve. + */ +static void +dmu_tx_delay(dmu_tx_t *tx, uint64_t dirty) +{ + dsl_pool_t *dp = tx->tx_pool; + uint64_t delay_min_bytes = + zfs_dirty_data_max * zfs_delay_min_dirty_percent / 100; + hrtime_t wakeup, min_tx_time, now; + + if (dirty <= delay_min_bytes) + return; + + /* + * The caller has already waited until we are under the max. + * We make them pass us the amount of dirty data so we don't + * have to handle the case of it being >= the max, which could + * cause a divide-by-zero if it's == the max. + */ + ASSERT3U(dirty, <, zfs_dirty_data_max); + + now = gethrtime(); + min_tx_time = zfs_delay_scale * + (dirty - delay_min_bytes) / (zfs_dirty_data_max - dirty); + if (now > tx->tx_start + min_tx_time) + return; + + min_tx_time = MIN(min_tx_time, zfs_delay_max_ns); + + DTRACE_PROBE3(delay__mintime, dmu_tx_t *, tx, uint64_t, dirty, + uint64_t, min_tx_time); + + mutex_enter(&dp->dp_lock); + wakeup = MAX(tx->tx_start + min_tx_time, + dp->dp_last_wakeup + min_tx_time); + dp->dp_last_wakeup = wakeup; + mutex_exit(&dp->dp_lock); + +#ifdef _KERNEL +#ifdef illumos + mutex_enter(&curthread->t_delay_lock); + while (cv_timedwait_hires(&curthread->t_delay_cv, + &curthread->t_delay_lock, wakeup, zfs_delay_resolution_ns, + CALLOUT_FLAG_ABSOLUTE | CALLOUT_FLAG_ROUNDUP) > 0) + continue; + mutex_exit(&curthread->t_delay_lock); +#else + pause_sbt("dmu_tx_delay", wakeup * SBT_1NS, + zfs_delay_resolution_ns * SBT_1NS, C_ABSOLUTE); +#endif +#else + hrtime_t delta = wakeup - gethrtime(); + struct timespec ts; + ts.tv_sec = delta / NANOSEC; + ts.tv_nsec = delta % NANOSEC; + (void) nanosleep(&ts, NULL); +#endif +} + static int dmu_tx_try_assign(dmu_tx_t *tx, txg_how_t txg_how) { @@ -948,6 +1104,12 @@ dmu_tx_try_assign(dmu_tx_t *tx, txg_how_t txg_how) return (SET_ERROR(ERESTART)); } + if (!tx->tx_waited && + dsl_pool_need_dirty_delay(tx->tx_pool)) { + tx->tx_wait_dirty = B_TRUE; + return (SET_ERROR(ERESTART)); + } + tx->tx_txg = txg_hold_open(tx->tx_pool, &tx->tx_txgh); tx->tx_needassign_txh = NULL; @@ -1072,6 +1234,10 @@ dmu_tx_unassign(dmu_tx_t *tx) * blocking, returns immediately with ERESTART. This should be used * whenever you're holding locks. On an ERESTART error, the caller * should drop locks, do a dmu_tx_wait(tx), and try again. + * + * (3) TXG_WAITED. Like TXG_NOWAIT, but indicates that dmu_tx_wait() + * has already been called on behalf of this operation (though + * most likely on a different tx). */ int dmu_tx_assign(dmu_tx_t *tx, txg_how_t txg_how) @@ -1079,12 +1245,16 @@ dmu_tx_assign(dmu_tx_t *tx, txg_how_t txg_how) int err; ASSERT(tx->tx_txg == 0); - ASSERT(txg_how == TXG_WAIT || txg_how == TXG_NOWAIT); + ASSERT(txg_how == TXG_WAIT || txg_how == TXG_NOWAIT || + txg_how == TXG_WAITED); ASSERT(!dsl_pool_sync_context(tx->tx_pool)); /* If we might wait, we must not hold the config lock. */ ASSERT(txg_how != TXG_WAIT || !dsl_pool_config_held(tx->tx_pool)); + if (txg_how == TXG_WAITED) + tx->tx_waited = B_TRUE; + while ((err = dmu_tx_try_assign(tx, txg_how)) != 0) { dmu_tx_unassign(tx); @@ -1103,18 +1273,48 @@ void dmu_tx_wait(dmu_tx_t *tx) { spa_t *spa = tx->tx_pool->dp_spa; + dsl_pool_t *dp = tx->tx_pool; ASSERT(tx->tx_txg == 0); ASSERT(!dsl_pool_config_held(tx->tx_pool)); - /* - * It's possible that the pool has become active after this thread - * has tried to obtain a tx. If that's the case then his - * tx_lasttried_txg would not have been assigned. - */ - if (spa_suspended(spa) || tx->tx_lasttried_txg == 0) { - txg_wait_synced(tx->tx_pool, spa_last_synced_txg(spa) + 1); + if (tx->tx_wait_dirty) { + /* + * dmu_tx_try_assign() has determined that we need to wait + * because we've consumed much or all of the dirty buffer + * space. + */ + mutex_enter(&dp->dp_lock); + while (dp->dp_dirty_total >= zfs_dirty_data_max) + cv_wait(&dp->dp_spaceavail_cv, &dp->dp_lock); + uint64_t dirty = dp->dp_dirty_total; + mutex_exit(&dp->dp_lock); + + dmu_tx_delay(tx, dirty); + + tx->tx_wait_dirty = B_FALSE; + + /* + * Note: setting tx_waited only has effect if the caller + * used TX_WAIT. Otherwise they are going to destroy + * this tx and try again. The common case, zfs_write(), + * uses TX_WAIT. + */ + tx->tx_waited = B_TRUE; + } else if (spa_suspended(spa) || tx->tx_lasttried_txg == 0) { + /* + * If the pool is suspended we need to wait until it + * is resumed. Note that it's possible that the pool + * has become active after this thread has tried to + * obtain a tx. If that's the case then tx_lasttried_txg + * would not have been set. + */ + txg_wait_synced(dp, spa_last_synced_txg(spa) + 1); } else if (tx->tx_needassign_txh) { + /* + * A dnode is assigned to the quiescing txg. Wait for its + * transaction to complete. + */ dnode_t *dn = tx->tx_needassign_txh->txh_dnode; mutex_enter(&dn->dn_mtx); |
