12 Commits

Author	SHA1	Message	Date
Matthew Ahrens	e8b96c6007	Illumos #4045 write throttle & i/o scheduler performance work ... 4045 zfs write throttle & i/o scheduler performance work 1. The ZFS i/o scheduler (vdev_queue.c) now divides i/os into 5 classes: sync read, sync write, async read, async write, and scrub/resilver. The scheduler issues a number of concurrent i/os from each class to the device. Once a class has been selected, an i/o is selected from this class using either an elevator algorithem (async, scrub classes) or FIFO (sync classes). The number of concurrent async write i/os is tuned dynamically based on i/o load, to achieve good sync i/o latency when there is not a high load of writes, and good write throughput when there is. See the block comment in vdev_queue.c (reproduced below) for more details. 2. The write throttle (dsl_pool_tempreserve_space() and txg_constrain_throughput()) is rewritten to produce much more consistent delays when under constant load. The new write throttle is based on the amount of dirty data, rather than guesses about future performance of the system. When there is a lot of dirty data, each transaction (e.g. write() syscall) will be delayed by the same small amount. This eliminates the "brick wall of wait" that the old write throttle could hit, causing all transactions to wait several seconds until the next txg opens. One of the keys to the new write throttle is decrementing the amount of dirty data as i/o completes, rather than at the end of spa_sync(). Note that the write throttle is only applied once the i/o scheduler is issuing the maximum number of outstanding async writes. See the block comments in dsl_pool.c and above dmu_tx_delay() (reproduced below) for more details. This diff has several other effects, including: * the commonly-tuned global variable zfs_vdev_max_pending has been removed; use per-class zfs_vdev_*_max_active values or zfs_vdev_max_active instead. * the size of each txg (meaning the amount of dirty data written, and thus the time it takes to write out) is now controlled differently. There is no longer an explicit time goal; the primary determinant is amount of dirty data. Systems that are under light or medium load will now often see that a txg is always syncing, but the impact to performance (e.g. read latency) is minimal. Tune zfs_dirty_data_max and zfs_dirty_data_sync to control this. * zio_taskq_batch_pct = 75 -- Only use 75% of all CPUs for compression, checksum, etc. This improves latency by not allowing these CPU-intensive tasks to consume all CPU (on machines with at least 4 CPU's; the percentage is rounded up). --matt APPENDIX: problems with the current i/o scheduler The current ZFS i/o scheduler (vdev_queue.c) is deadline based. The problem with this is that if there are always i/os pending, then certain classes of i/os can see very long delays. For example, if there are always synchronous reads outstanding, then no async writes will be serviced until they become "past due". One symptom of this situation is that each pass of the txg sync takes at least several seconds (typically 3 seconds). If many i/os become "past due" (their deadline is in the past), then we must service all of these overdue i/os before any new i/os. This happens when we enqueue a batch of async writes for the txg sync, with deadlines 2.5 seconds in the future. If we can't complete all the i/os in 2.5 seconds (e.g. because there were always reads pending), then these i/os will become past due. Now we must service all the "async" writes (which could be hundreds of megabytes) before we service any reads, introducing considerable latency to synchronous i/os (reads or ZIL writes). Notes on porting to ZFS on Linux: - zio_t gained new members io_physdone and io_phys_children. Because object caches in the Linux port call the constructor only once at allocation time, objects may contain residual data when retrieved from the cache. Therefore zio_create() was updated to zero out the two new fields. - vdev_mirror_pending() relied on the depth of the per-vdev pending queue (vq->vq_pending_tree) to select the least-busy leaf vdev to read from. This tree has been replaced by vq->vq_active_tree which is now used for the same purpose. - vdev_queue_init() used the value of zfs_vdev_max_pending to determine the number of vdev I/O buffers to pre-allocate. That global no longer exists, so we instead use the sum of the *_max_active values for each of the five I/O classes described above. - The Illumos implementation of dmu_tx_delay() delays a transaction by sleeping in condition variable embedded in the thread (curthread->t_delay_cv). We do not have an equivalent CV to use in Linux, so this change replaced the delay logic with a wrapper called zfs_sleep_until(). This wrapper could be adopted upstream and in other downstream ports to abstract away operating system-specific delay logic. - These tunables are added as module parameters, and descriptions added to the zfs-module-parameters.5 man page. spa_asize_inflation zfs_deadman_synctime_ms zfs_vdev_max_active zfs_vdev_async_write_active_min_dirty_percent zfs_vdev_async_write_active_max_dirty_percent zfs_vdev_async_read_max_active zfs_vdev_async_read_min_active zfs_vdev_async_write_max_active zfs_vdev_async_write_min_active zfs_vdev_scrub_max_active zfs_vdev_scrub_min_active zfs_vdev_sync_read_max_active zfs_vdev_sync_read_min_active zfs_vdev_sync_write_max_active zfs_vdev_sync_write_min_active zfs_dirty_data_max_percent zfs_delay_min_dirty_percent zfs_dirty_data_max_max_percent zfs_dirty_data_max zfs_dirty_data_max_max zfs_dirty_data_sync zfs_delay_scale The latter four have type unsigned long, whereas they are uint64_t in Illumos. This accommodates Linux's module_param() supported types, but means they may overflow on 32-bit architectures. The values zfs_dirty_data_max and zfs_dirty_data_max_max are the most likely to overflow on 32-bit systems, since they express physical RAM sizes in bytes. In fact, Illumos initializes zfs_dirty_data_max_max to 2^32 which does overflow. To resolve that, this port instead initializes it in arc_init() to 25% of physical RAM, and adds the tunable zfs_dirty_data_max_max_percent to override that percentage. While this solution doesn't completely avoid the overflow issue, it should be a reasonable default for most systems, and the minority of affected systems can work around the issue by overriding the defaults. - Fixed reversed logic in comment above zfs_delay_scale declaration. - Clarified comments in vdev_queue.c regarding when per-queue minimums take effect. - Replaced dmu_tx_write_limit in the dmu_tx kstat file with dmu_tx_dirty_delay and dmu_tx_dirty_over_max. The first counts how many times a transaction has been delayed because the pool dirty data has exceeded zfs_delay_min_dirty_percent. The latter counts how many times the pool dirty data has exceeded zfs_dirty_data_max (which we expect to never happen). - The original patch would have regressed the bug fixed in zfsonlinux/zfs@c418410, which prevented users from setting the zfs_vdev_aggregation_limit tuning larger than SPA_MAXBLOCKSIZE. A similar fix is added to vdev_queue_aggregate(). - In vdev_queue_io_to_issue(), dynamically allocate 'zio_t search' on the heap instead of the stack. In Linux we can't afford such large structures on the stack. Reviewed by: George Wilson <george.wilson@delphix.com> Reviewed by: Adam Leventhal <ahl@delphix.com> Reviewed by: Christopher Siden <christopher.siden@delphix.com> Reviewed by: Ned Bass <bass6@llnl.gov> Reviewed by: Brendan Gregg <brendan.gregg@joyent.com> Approved by: Robert Mustacchi <rm@joyent.com> References: http://www.illumos.org/issues/4045 illumos/illumos-gate@69962b5647 Ported-by: Ned Bass <bass6@llnl.gov> Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov> Closes #1913	2013-12-06 09:32:43 -08:00
George Wilson	5d1f7fb647	Illumos #3956, #3957, #3958, #3959, #3960, #3961, #3962 ... 3956 ::vdev -r should work with pipelines 3957 ztest should update the cachefile before killing itself 3958 multiple scans can lead to partial resilvering 3959 ddt entries are not always resilvered 3960 dsl_scan can skip over dedup-ed blocks if physical birth != logical birth 3961 freed gang blocks are not resilvered and can cause pool to suspend 3962 ztest should print out zfs debug buffer before exiting Reviewed by: Matthew Ahrens <mahrens@delphix.com> Reviewed by: Adam Leventhal <ahl@delphix.com> Approved by: Richard Lowe <richlowe@richlowe.net> References: https://www.illumos.org/issues/3956 https://www.illumos.org/issues/3957 https://www.illumos.org/issues/3958 https://www.illumos.org/issues/3959 https://www.illumos.org/issues/3960 https://www.illumos.org/issues/3961 https://www.illumos.org/issues/3962 illumos/illumos-gate@b4952e17e8 Ported-by: Richard Yao <ryao@gentoo.org> Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov> Porting notes: 1. zfs_dbgmsg_print() is only used in userland. Since we do not have mdb on Linux, it does not make sense to make it available in the kernel. This means that a build failure will occur if any future kernel patch depends on it. However, that is unlikely given that this functionality was added to support zdb. 2. zfs_dbgmsg_print() is only invoked for -VVV or greater log levels. This preserves the existing behavior of minimal noise when running with -V, and -VV. 3. In vdev_config_generate() the call to nvlist_alloc() was not changed to fnvlist_alloc() because we must pass KM_PUSHPAGE in the txg_sync context.	2013-11-05 12:23:05 -08:00
Will Andrews	d3cc8b152e	Illumos #3742 ... 3742 zfs comments need cleaner, more consistent style Reviewed by: Matthew Ahrens <mahrens@delphix.com> Reviewed by: George Wilson <george.wilson@delphix.com> Reviewed by: Eric Schrock <eric.schrock@delphix.com> Approved by: Christopher Siden <christopher.siden@delphix.com> References: https://www.illumos.org/issues/3742 illumos/illumos-gate@f717074149 Ported-by: Richard Yao <ryao@gentoo.org> Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov> Issue #1775 Porting notes: 1. The change to zfs_vfsops.c was dropped because it involves zfs_mount_label_policy, which does not exist in the Linux port.	2013-11-04 10:55:25 -08:00
Matthew Ahrens	cb682a173a	Illumos #3618 ::zio dcmd does not show timestamp data ... 3618 ::zio dcmd does not show timestamp data Reviewed by: Adam Leventhal <ahl@delphix.com> Reviewed by: George Wilson <gwilson@zfsmail.com> Reviewed by: Christopher Siden <christopher.siden@delphix.com> Reviewed by: Garrett D'Amore <garrett@damore.org> Approved by: Dan McDonald <danmcd@nexenta.com> References: http://www.illumos.org/issues/3618 illumos/illumos-gate@c55e05cb35 Notes on porting to ZFS on Linux: The original changeset mostly deals with mdb ::zio dcmd. However, in order to provide the requested functionality it modifies vdev and zio structures to keep the timing data in nanoseconds instead of ticks. It is these changes that are ported over in the commit in hand. One visible change of this commit is that the default value of 'zfs_vdev_time_shift' tunable is changed: zfs_vdev_time_shift = 6 to zfs_vdev_time_shift = 29 The original value of 6 was inherited from OpenSolaris and was subotimal - since it shifted the raw tick value - it didn't compensate for different tick frequencies on Linux and OpenSolaris. The former has HZ=1000, while the latter HZ=100. (Which itself led to other interesting performance anomalies under non-trivial load. The deadline scheduler delays the IO according to its priority - the lower priority the further the deadline is set. The delay is measured in units of "shifted ticks". Since the HZ value was 10 times higher, the delay units were 10 times shorter. Thus really low priority IO like resilver (delay is 10 units) and scrub (delay is 20 units) were scheduled much sooner than intended. The overall effect is that resilver and scrub IO consumed more bandwidth at the expense of the other IO.) Now that the bookkeeping is done is nanoseconds the shift behaves correctly for any tick frequency (HZ). Ported-by: Cyril Plisko <cyril.plisko@mountall.com> Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov> Closes #1643	2013-08-12 16:46:50 -07:00
George.Wilson	cc92e9d0c3	3246 ZFS I/O deadman thread ... Reviewed by: Matt Ahrens <matthew.ahrens@delphix.com> Reviewed by: Eric Schrock <eric.schrock@delphix.com> Reviewed by: Christopher Siden <chris.siden@delphix.com> Approved by: Garrett D'Amore <garrett@damore.org> NOTES: This patch has been reworked from the original in the following ways to accomidate Linux ZFS implementation *) Usage of the cyclic interface was replaced by the delayed taskq interface. This avoids the need to implement new compatibility code and allows us to rely on the existing taskq implementation. *) An extern for zfs_txg_synctime_ms was added to sys/dsl_pool.h because declaring externs in source files as was done in the original patch is just plain wrong. *) Instead of panicing the system when the deadman triggers a zevent describing the blocked vdev and the first pending I/O is posted. If the panic behavior is desired Linux provides other generic methods to panic the system when threads are observed to hang. *) For reference, to delay zios by 30 seconds for testing you can use zinject as follows: 'zinject -d <vdev> -D30 <pool>' References: illumos/illumos-gate@283b84606b https://www.illumos.org/issues/3246 Ported-by: Brian Behlendorf <behlendorf1@llnl.gov> Closes #1396	2013-05-01 17:05:52 -07:00
Richard Yao	b01615d5ac	Constify structures containing function pointers ... The PaX team modified the kernel's modpost to report writeable function pointers as section mismatches because they are potential exploit targets. We could ignore the warnings, but their presence can obscure actual issues. Proper const correctness can also catch programming mistakes. Building the kernel modules against a PaX/GrSecurity patched Linux 3.4.2 kernel reports 133 section mismatches prior to this patch. This patch eliminates 130 of them. The quantity of writeable function pointers eliminated by constifying each structure is as follows: vdev_opts_t 52 zil_replay_func_t 24 zio_compress_info_t 24 zio_checksum_info_t 9 space_map_ops_t 7 arc_byteswap_func_t 5 The remaining 3 writeable function pointers cannot be addressed by this patch. 2 of them are in zpl_fs_type. The kernel's sget function requires that this be non-const. The final writeable function pointer is created by SPL_SHRINKER_DECLARE. The kernel's set_shrinker() and remove_shrinker() functions also require that this be non-const. Signed-off-by: Richard Yao <ryao@cs.stonybrook.edu> Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov> Closes #1300	2013-03-04 08:49:32 -08:00
Christopher Siden	9ae529ec5d	Illumos #2619 and #2747 ... 2619 asynchronous destruction of ZFS file systems 2747 SPA versioning with zfs feature flags Reviewed by: Matt Ahrens <mahrens@delphix.com> Reviewed by: George Wilson <gwilson@delphix.com> Reviewed by: Richard Lowe <richlowe@richlowe.net> Reviewed by: Dan Kruchinin <dan.kruchinin@gmail.com> Approved by: Eric Schrock <Eric.Schrock@delphix.com> References: illumos/illumos-gate@53089ab7c8 illumos/illumos-gate@ad135b5d64 illumos changeset: 13700:2889e2596bd6 https://www.illumos.org/issues/2619 https://www.illumos.org/issues/2747 NOTE: The grub specific changes were not ported. This change must be made to the Linux grub packages. Ported-by: Brian Behlendorf <behlendorf1@llnl.gov>	2013-01-08 10:35:35 -08:00
Etienne Dechamps	920dd524fb	Add FASTWRITE algorithm for synchronous writes. ... Currently, ZIL blocks are spread over vdevs using hint block pointers managed by the ZIL commit code and passed to metaslab_alloc(). Spreading log blocks accross vdevs is important for performance: indeed, using mutliple disks in parallel decreases the ZIL commit latency, which is the main performance metric for synchronous writes. However, the current implementation suffers from the following issues: 1) It would be best if the ZIL module was not aware of such low-level details. They should be handled by the ZIO and metaslab modules; 2) Because the hint block pointer is managed per log, simultaneous commits from multiple logs might use the same vdevs at the same time, which is inefficient; 3) Because dmu_write() does not honor the block pointer hint, indirect writes are not spread. The naive solution of rotating the metaslab rotor each time a block is allocated for the ZIL or dmu_sync() doesn't work in practice because the first ZIL block to be written is actually allocated during the previous commit. Consequently, when metaslab_alloc() decides the vdev for this block, it will do so while a bunch of other allocations are happening at the same time (from dmu_sync() and other ZILs). This means the vdev for this block is chosen more or less at random. When the next commit happens, there is a high chance (especially when the number of blocks per commit is slightly less than the number of the disks) that one disk will have to write two blocks (with a potential seek) while other disks are sitting idle, which defeats spreading and increases the commit latency. This commit introduces a new concept in the metaslab allocator: fastwrites. Basically, each top-level vdev maintains a counter indicating the number of synchronous writes (from dmu_sync() and the ZIL) which have been allocated but not yet completed. When the metaslab is called with the FASTWRITE flag, it will choose the vdev with the least amount of pending synchronous writes. If there are multiple vdevs with the same value, the first matching vdev (starting from the rotor) is used. Once metaslab_alloc() has decided which vdev the block is allocated to, it updates the fastwrite counter for this vdev. The rationale goes like this: when an allocation is done with FASTWRITE, it "reserves" the vdev until the data is written. Until then, all future allocations will naturally avoid this vdev, even after a full rotation of the rotor. As a result, pending synchronous writes at a given point in time will be nicely spread over all vdevs. This contrasts with the previous algorithm, which is based on the implicit assumption that blocks are written instantaneously after they're allocated. metaslab_fastwrite_mark() and metaslab_fastwrite_unmark() are used to manually increase or decrease fastwrite counters, respectively. They should be used with caution, as there is no per-BP tracking of fastwrite information, so leaks and "double-unmarks" are possible. There is, however, an assert in the vdev teardown code which will fire if the fastwrite counters are not zero when the pool is exported or the vdev removed. Note that as stated above, marking is also done implictly by metaslab_alloc(). ZIO also got a new FASTWRITE flag; when it is used, ZIO will pass it to the metaslab when allocating (assuming ZIO does the allocation, which is only true in the case of dmu_sync). This flag will also trigger an unmark when zio_done() fires. A side-effect of the new algorithm is that when a ZIL stops being used, its last block can stay in the pending state (allocated but not yet written) for a long time, polluting the fastwrite counters. To avoid that, I've implemented a somewhat crude but working solution which unmarks these pending blocks in zil_sync(), thus guaranteeing that linguering fastwrites will get pruned at each sync event. The best performance improvements are observed with pools using a large number of top-level vdevs and heavy synchronous write workflows (especially indirect writes and concurrent writes from multiple ZILs). Real-life testing shows a 200% to 300% performance increase with indirect writes and various commit sizes. Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov> Issue #1013	2012-10-17 08:56:41 -07:00
Chris Siden	1bd201e70d	Illumos #1948: zpool list should show more detailed pool info ... Reviewed by: Adam Leventhal <ahl@delphix.com> Reviewed by: Matt Ahrens <matt@delphix.com> Reviewed by: Eric Schrock <eric.schrock@delphix.com> Reviewed by: Richard Lowe <richlowe@richlowe.net> Reviewed by: Albert Lee <trisk@nexenta.com> Reviewed by: Dan McDonald <danmcd@nexenta.com> Reviewed by: Garrett D'Amore <garrett@damore.org> Approved by: Eric Schrock <eric.schrock@delphix.com> References: https://www.illumos.org/issues/1948 Ported by: Martin Matuska <martin@matuska.org> Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov> Closes #685	2012-09-19 13:39:05 -07:00
Brian Behlendorf	86dd0fd922	Pre-allocate vdev I/O buffers ... The vdev queue layer may require a small number of buffers when attempting to create aggregate I/O requests. Rather than attempting to allocate them from the global zio buffers, which is slow under memory pressure, it makes sense to pre-allocate them because... 1) These buffers are short lived. They are only required for the life of a single I/O at which point they can be used by the next I/O. 2) The maximum number of concurrent buffers needed by a vdev is small. It's roughly limited by the zfs_vdev_max_pending tunable which defaults to 10. By keeping a small list of these buffer per-vdev we can ensure one is always available when we need it. This significantly reduces contention on the vq->vq_lock, because we no longer need to perform a slow allocation under this lock. This is particularly important when memory is already low on the system. It would probably be wise to extend the use of these buffers beyond aggregate I/O and in to the raidz implementation. The inability to quickly allocate buffer for the parity stripes could result in similiar problems. Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>	2012-08-27 12:01:37 -07:00
George Wilson	5ffb9d1d05	Illumos #1951: leaking a vdev when removing an l2cache device ... 1952 memory leak when adding a file-based l2arc device 1954 leak in ZFS from metaslab_group_create and zfs_ereport_checksum Reviewed by: Adam Leventhal <ahl@delphix.com> Reviewed by: Matt Ahrens <matt@delphix.com> Reviewed by: Eric Schrock <eric.schrock@delphix.com> Reviewed by: Bill Pijewski <wdp@joyent.com> Reviewed by: Dan McDonald <danmcd@nexenta.com> Approved by: Eric Schrock <eric.schrock@delphix.com> References to Illumos issues: https://www.illumos.org/issues/1951 https://www.illumos.org/issues/1952 https://www.illumos.org/issues/1954 Ported-by: Richard Yao <ryao@cs.stonybrook.edu> Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov> Closes #650	2012-04-11 11:32:06 -07:00
Brian Behlendorf	6283f55ea1	Support custom build directories and move includes ... One of the neat tricks an autoconf style project is capable of is allow configurion/building in a directory other than the source directory. The major advantage to this is that you can build the project various different ways while making changes in a single source tree. For example, this project is designed to work on various different Linux distributions each of which work slightly differently. This means that changes need to verified on each of those supported distributions perferably before the change is committed to the public git repo. Using nfs and custom build directories makes this much easier. I now have a single source tree in nfs mounted on several different systems each running a supported distribution. When I make a change to the source base I suspect may break things I can concurrently build from the same source on all the systems each in their own subdirectory. wget -c http://github.com/downloads/behlendorf/zfs/zfs-x.y.z.tar.gz tar -xzf zfs-x.y.z.tar.gz cd zfs-x-y-z ------------------------- run concurrently ---------------------- <ubuntu system> <fedora system> <debian system> <rhel6 system> mkdir ubuntu mkdir fedora mkdir debian mkdir rhel6 cd ubuntu cd fedora cd debian cd rhel6 ../configure ../configure ../configure ../configure make make make make make check make check make check make check This change also moves many of the include headers from individual incude/sys directories under the modules directory in to a single top level include directory. This has the advantage of making the build rules cleaner and logically it makes a bit more sense.	2010-09-08 12:38:56 -07:00