The /proc/diskstats accounting needs to be explicitly enabled
for block devices which do not use multi-queue.
Reviewed-by: Tony Nguyen <tony.nguyen@delphix.com>
Reviewed-by: George Melikov <mail@gmelikov.ru>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#12440Closes#12066
In Linux 5.14, blk_alloc_queue is no longer exported, and its usage
has been superseded by blk_alloc_disk, which returns a gendisk struct
from which we can still retrieve the struct request_queue* that is
needed in the one place where it is used. This also replaces the call
to alloc_disk(minors), and minors is now set via struct member
assignment.
Reviewed-by: Tony Nguyen <tony.nguyen@delphix.com>
Reviewed-by: Olaf Faaland <faaland1@llnl.gov>
Reviewed-by: Coleman Kane <ckane@colemankane.org>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#12362Closes#12409
Linux kernel commit 0f00b82e5413571ed225ddbccad6882d7ea60bc7 removes the
revalidate_disk() handler from struct block_device_operations. This
caused a regression, and this commit eliminates the call to it and the
assignment in the block_device_operations static handler assignment
code, when configure identifies that the kernel doesn't support that
API handler.
Reviewed-by: Colin Ian King <colin.king@canonical.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Coleman Kane <ckane@colemankane.org>
Closes#11967Closes#11977
zil_replaying(zil, tx) has the side-effect of informing the ZIL that an
entry has been replayed in the (still open) tx. The ZIL uses that
information to record the replay progress in the ZIL header when that
tx's txg syncs.
ZPL log entries are not idempotent and logically dependent and thus
calling zil_replaying() is necessary for correctness.
For ZVOLs the question of correctness is more nuanced: ZVOL logs only
TX_WRITE and TX_TRUNCATE, both of which are idempotent. Logical
dependencies between two records exist only if the write or discard
request had sync semantics or if the ranges affected by the records
overlap.
Thus, at a first glance, it would be correct to restart replay from
the beginning if we crash before replay completes. But this does not
address the following scenario:
Assume one log record per LWB.
The chain on disk is
HDR -> 1:W(1, "A") -> 2:W(1, "B") -> 3:W(2, "X") -> 4:W(3, "Z")
where N:W(O, C) represents log entry number N which is a TX_WRITE of C
to offset A.
We replay 1, 2 and 3 in one txg, sync that txg, then crash.
Bit flips corrupt 2, 3, and 4.
We come up again and restart replay from the beginning because
we did not call zil_replaying() during replay.
We replay 1 again, then interpret 2's invalid checksum as the end
of the ZIL chain and call replay done.
The replayed zvol content is "AX".
If we had called zil_replaying() the HDR would have pointed to 3
and our resumed replay would not have replayed anything because
3 was corrupted, resulting in zvol content "BX".
If 3 logically depends on 2 then the replay corrupted the ZVOL_OBJ's
contents.
This patch adds the zil_replaying() calls to the replay functions.
Since the callbacks in the replay function need the zilog_t* pointer
so that they can call zil_replaying() we open the ZIL while
replaying in zvol_create_minor(). We also verify that replay has
been done when on-demand-opening the ZIL on the first modifying
bio.
Reviewed-by: Matthew Ahrens <mahrens@delphix.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Christian Schwarz <me@cschwarz.com>
Closes#11667
The spl_kmem_alloc showed up in some flamegraphs in a single-threaded
4k sync write workload at 85k IOPS on an
Intel(R) Xeon(R) Silver 4215 CPU @ 2.50GHz.
Certainly not a huge win but I believe the change is clean and
easy to maintain down the road.
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Matthew Ahrens <mahrens@delphix.com>
Signed-off-by: Christian Schwarz <me@cschwarz.com>
Closes#11666
The struct bio member bi_disk was moved underneath a new member named
bi_bdev. So all attempts to reference bio->bi_disk need to now become
bio->bi_bdev->bd_disk.
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Coleman Kane <ckane@colemankane.org>
Closes#11639
In FreeBSD the struct uio was just a typedef to uio_t. In order to
extend this struct, outside of the definition for the struct uio, the
struct uio has been embedded inside of a uio_t struct.
Also renamed all the uio_* interfaces to be zfs_uio_* to make it clear
this is a ZFS interface.
Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Reviewed-by: Jorgen Lundman <lundman@lundman.net>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Brian Atkinson <batkinson@lanl.gov>
Closes#11438
As of 5.11 the blk_register_region() and blk_unregister_region()
functions have been retired. This isn't a problem since add_disk()
has implicitly allocated minor numbers for a very long time.
Reviewed-by: Rafael Kitover <rkitover@gmail.com>
Reviewed-by: Coleman Kane <ckane@colemankane.org>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#11387Closes#11390
Both revalidate_disk_size() and revalidate_disk() have been removed.
Functionally this isn't a problem because we only relied on these
functions to call zvol_revalidate_disk() for us and to perform any
additional handling which might be needed for that kernel version.
When neither are available we know there's no additional handling
needed and we can directly call zvol_revalidate_disk().
Reviewed-by: Rafael Kitover <rkitover@gmail.com>
Reviewed-by: Coleman Kane <ckane@colemankane.org>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#11387Closes#11390
The generic IO accounting functions have been removed in favor of the
bio_start_io_acct() and bio_end_io_acct() functions which provide a
better interface. These new functions were introduced in the 5.8
kernels but it wasn't until the 5.11 kernel that the previous generic
IO accounting interfaces were removed.
This commit updates the blk_generic_*_io_acct() wrappers to provide
and interface similar to the updated kernel interface. It's slightly
different because for older kernels we need to pass the request queue
as well as the bio.
Reviewed-by: Rafael Kitover <rkitover@gmail.com>
Reviewed-by: Coleman Kane <ckane@colemankane.org>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#11387Closes#11390
The lookup_bdev() function has been updated to require a dev_t
be passed as the second argument. This is actually pretty nice
since the major number stored in the dev_t was the only part we
were interested in. This allows to us avoid handling the bdev
entirely. The vdev_lookup_bdev() wrapper was updated to emulate
the behavior of the new lookup_bdev() for all supported kernels.
Reviewed-by: Rafael Kitover <rkitover@gmail.com>
Reviewed-by: Coleman Kane <ckane@colemankane.org>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#11387Closes#11390
Commit 59b68723 added a configure check for 5.10, which removed
revalidate_disk(), and conditionally replaced it's usage with a call to
the new revalidate_disk_size() function. However, the old function also
invoked the device's registered callback, in our case
zvol_revalidate_disk(). This commit adds a call to zvol_revalidate_disk()
in zvol_update_volsize() to make sure the code path stays the same.
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Michael D Labriola <michael.d.labriola@gmail.com>
Closes#11358
As of the 5.10 kernel the generic splice compatibility code has been
removed. All filesystems are now responsible for registering a
->splice_read and ->splice_write callback to support this operation.
The good news is the VFS provided generic_file_splice_read() and
iter_file_splice_write() callbacks can be used provided the ->iter_read
and ->iter_write callback support pipes. However, this is currently
not the case and only iovecs and bvecs (not pipes) are ever attached
to the uio structure.
This commit changes that by allowing full iov_iter structures to be
attached to uios. Ever since the 4.9 kernel the iov_iter structure
has supported iovecs, kvecs, bvevs, and pipes so it's desirable to
pass the entire thing when possible. In conjunction with this the
uio helper functions (i.e uiomove(), uiocopy(), etc) have been
updated to understand the new UIO_ITER type.
Note that using the kernel provided uio_iter interfaces allowed the
existing Linux specific uio handling code to be simplified. When
there's no longer a need to support kernel's older than 4.9, then
it will be possible to remove the iovec and bvec members from the
uio structure and always use a uio_iter. Until then we need to
maintain all of the existing types for older kernels.
Some additional refactoring and cleanup was included in this change:
- Added checks to configure to detect available iov_iter interfaces.
Some are available all the way back to the 3.10 kernel and are used
when available. In particular, uio_prefaultpages() now always uses
iov_iter_fault_in_readable() which is available for all supported
kernels.
- The unused UIO_USERISPACE type has been removed. It is no longer
needed now that the uio_seg enum is platform specific.
- Moved zfs_uio.c from the zcommon.ko module to the Linux specific
platform code for the zfs.ko module. This gets it out of libzfs
where it was never needed and keeps this Linux specific code out
of the common sources.
- Removed unnecessary O_APPEND handling from zfs_iter_write(), this
is redundant and O_APPEND is already handled in zfs_write();
Reviewed-by: Colin Ian King <colin.king@canonical.com>
Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#11351
- Don't leave fstrans set when passed a snapshot
- Don't remove minor if volmode already matches new value
- (FreeBSD) Wait for GEOM ops to complete before trying
remove (at create time GEOM will be "tasting" in parallel)
- (FreeBSD) Don't leak zvol_state_lock on open if zv == NULL
- (FreeBSD) Don't try to unlock zv->zv_state lock if zv == NULL
Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Matt Macy <mmacy@FreeBSD.org>
Closes#11199
A new function was added named revalidate_disk_size() and the old
revalidate_disk() appears to have been deprecated. As the only ZFS
code that calls this function is zvol_update_volsize, swapping the
old function call out for the new one should be all that is required.
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Coleman Kane <ckane@colemankane.org>
Closes#11085
Kernel 5.10 removed check_disk_change() in favor of callers using
the faster bdev_check_media_change() instead, and explicitly forcing
bdev revalidation when they desire that behavior. To preserve prior
behavior, I have wrapped this into a zfs_check_media_change() macro
that calls an inline function for the new API that mimics the old
behavior when check_disk_change() doesn't exist, and just calls
check_disk_change() if it exists.
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Coleman Kane <ckane@colemankane.org>
Closes#11085
Using more specific assert variants gives better messages on failure.
No functional change.
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Reviewed-by: Matt Macy <mmacy@FreeBSD.org>
Signed-off-by: Ryan Moeller <ryan@iXsystems.com>
Closes#11117
The zfs_fsync, zfs_read, and zfs_write function are almost identical
between Linux and FreeBSD. With a little refactoring they can be
moved to the common code which is what is done by this commit.
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Signed-off-by: Matt Macy <mmacy@FreeBSD.org>
Closes#11078
The make_request_fn and associated API was replaced recently in a
Linux 5.9 merge, to replace its functionality with a new submit_bio
member in struct block_device_operations.
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Coleman Kane <ckane@colemankane.org>
Closes#10696
Mark functions used only in the same translation unit as static. This
only includes functions that do not have a prototype in a header file
either.
Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
Closes#10470
Expand the FreeBSD spl for kstats to support all current types
Move the dataset_kstats_t back to zvol_state_t from zfs_state_os_t
now that it is common once again
```
kstat.zfs/mypool.dataset.objset-0x10b.nunlinked: 0
kstat.zfs/mypool.dataset.objset-0x10b.nunlinks: 0
kstat.zfs/mypool.dataset.objset-0x10b.nread: 150528
kstat.zfs/mypool.dataset.objset-0x10b.reads: 48
kstat.zfs/mypool.dataset.objset-0x10b.nwritten: 134217728
kstat.zfs/mypool.dataset.objset-0x10b.writes: 1024
kstat.zfs/mypool.dataset.objset-0x10b.dataset_name: mypool/datasetname
```
Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Reviewed by: Sean Eric Fagan <sef@ixsystems.com>
Reviewed-by: Serapheim Dimitropoulos <serapheim@delphix.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Allan Jude <allan@klarasystems.com>
Closes#10386
We can improve the performance of writes to zvols by using
dmu_tx_hold_write_by_dnode() instead of dmu_tx_hold_write(). This
reduces lock contention on the first block of the dnode object, and also
reduces the amount of CPU needed. The benefit will be highest with
multi-threaded async writes (i.e. writes that don't call zil_commit()).
Reviewed-by: Jorgen Lundman <lundman@lundman.net>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Tony Nguyen <tony.nguyen@delphix.com>
Signed-off-by: Matthew Ahrens <mahrens@delphix.com>
Closes#10184
Commit https://github.com/torvalds/linux/commit/3d745ea5 simplified
the blk_alloc_queue() interface by updating it to take the request
queue as an argument. Add a wrapper function which accepts the new
arguments and internally uses the available interfaces.
Other minor changes include increasing the Linux-Maximum to 5.6 now
that 5.6 has been released. It was not bumped to 5.7 because this
release has not yet been finalized and is still subject to change.
Added local 'struct zvol_state_os *zso' variable to zvol_alloc.
Reviewed-by: George Melikov <mail@gmelikov.ru>
Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#10181Closes#10187
== Summary ==
Prior to this change, sync writes to a zvol are processed serially.
This commit makes zvols process concurrently outstanding sync writes in
parallel, similar to how reads and async writes are already handled.
The result is that the throughput of sync writes is tripled.
== Background ==
When a write comes in for a zvol (e.g. over iscsi), it is processed by
calling `zvol_request()` to initiate the operation. ZFS is expected to
later call `BIO_END_IO()` when the operation completes (possibly from a
different thread). There are a limited number of threads that are
available to call `zvol_request()` - one one per iscsi client (unless
using MC/S). Therefore, to ensure good performance, the latency of
`zvol_request()` is important, so that many i/o operations to the zvol
can be processed concurrently. In other words, if the client has
multiple outstanding requests to the zvol, the zvol should have multiple
outstanding requests to the storage hardware (i.e. issue multiple
concurrent `zio_t`'s).
For reads, and async writes (i.e. writes which can be acknowledged
before the data reaches stable storage), `zvol_request()` achieves low
latency by dispatching the bulk of the work (including waiting for i/o
to disk) to a taskq. The taskq callback (`zvol_read()` or
`zvol_write()`) blocks while waiting for the i/o to disk to complete.
The `zvol_taskq` has 32 threads (by default), so we can have up to 32
concurrent i/os to disk in service of requests to zvols.
However, for sync writes (i.e. writes which must be persisted to stable
storage before they can be acknowledged, by calling `zil_commit()`),
`zvol_request()` does not use `zvol_taskq`. Instead it blocks while
waiting for the ZIL write to disk to complete. This has the effect of
serializing sync writes to each zvol. In other words, each zvol will
only process one sync write at a time, waiting for it to be written to
the ZIL before accepting the next request.
The same issue applies to FLUSH operations, for which `zvol_request()`
calls `zil_commit()` directly.
== Description of change ==
This commit changes `zvol_request()` to use
`taskq_dispatch_ent(zvol_taskq)` for sync writes, and FLUSh operations.
Therefore we can have up to 32 threads (the taskq threads)
simultaneously calling `zil_commit()`, for a theoretical performance
improvement of up to 32x.
To avoid the locking issue described in the comment (which this commit
removes), we acquire the rangelock from the taskq callback (e.g.
`zvol_write()`) rather than from `zvol_request()`. This applies to all
writes (sync and async), reads, and discard operations. This means that
multiple simultaneously-outstanding i/o's which access the same block
can complete in any order. This was previously thought to be incorrect,
but a review of the block device interface requirements revealed that
this is fine - the order is inherently not defined. The shorter hold
time of the rangelock should also have a slight performance improvement.
For an additional slight performance improvement, we use
`taskq_dispatch_ent()` instead of `taskq_dispatch()`, which avoids a
`kmem_alloc()` and eliminates a failure mode. This applies to all
writes (sync and async), reads, and discard operations.
== Performance results ==
We used a zvol as an iscsi target (server) for a Windows initiator
(client), with a single connection (the default - i.e. not MC/S).
We used `diskspd` to generate a workload with 4 threads, doing 1MB
writes to random offsets in the zvol. Without this change we get
231MB/s, and with the change we get 728MB/s, which is 3.15x the original
performance.
We ran a real-world workload, restoring a MSSQL database, and saw
throughput 2.5x the original.
We saw more modest performance wins (typically 1.5x-2x) when using MC/S
with 4 connections, and with different number of client threads (1, 8,
32).
Reviewed-by: Tony Nguyen <tony.nguyen@delphix.com>
Reviewed-by: Pavel Zakharov <pavel.zakharov@delphix.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Matthew Ahrens <mahrens@delphix.com>
Closes#10163
When we finish a zfs receive, dmu_recv_end_sync() calls
zvol_create_minors(async=TRUE). This kicks off some other threads that
create the minor device nodes (in /dev/zvol/poolname/...). These async
threads call zvol_prefetch_minors_impl() and zvol_create_minor(), which
both call dmu_objset_own(), which puts a "long hold" on the dataset.
Since the zvol minor node creation is asynchronous, this can happen
after the `ZFS_IOC_RECV[_NEW]` ioctl and `zfs receive` process have
completed.
After the first receive ioctl has completed, userland may attempt to do
another receive into the same dataset (e.g. the next incremental
stream). This second receive and the asynchronous minor node creation
can interfere with one another in several different ways, because they
both require exclusive access to the dataset:
1. When the second receive is finishing up, dmu_recv_end_check() does
dsl_dataset_handoff_check(), which can fail with EBUSY if the async
minor node creation already has a "long hold" on this dataset. This
causes the 2nd receive to fail.
2. The async udev rule can fail if zvol_id and/or systemd-udevd try to
open the device while the the second receive's async attempt at minor
node creation owns the dataset (via zvol_prefetch_minors_impl). This
causes the minor node (/dev/zd*) to exist, but the udev-generated
/dev/zvol/... to not exist.
3. The async minor node creation can silently fail with EBUSY if the
first receive's zvol_create_minor() trys to own the dataset while the
second receive's zvol_prefetch_minors_impl already owns the dataset.
To address these problems, this change synchronously creates the minor
node. To avoid the lock ordering problems that the asynchrony was
introduced to fix (see #3681), we create the minor nodes from open
context, with no locks held, rather than from syncing contex as was
originally done.
Implementation notes:
We generally do not need to traverse children or prefetch anything (e.g.
when running the recv, snapshot, create, or clone subcommands of zfs).
We only need recursion when importing/opening a pool and when loading
encryption keys. The existing recursive, asynchronous, prefetching code
is preserved for use in these cases.
Channel programs may need to create zvol minor nodes, when creating a
snapshot of a zvol with the snapdev property set. We figure out what
snapshots are created when running the LUA program in syncing context.
In this case we need to remember what snapshots were created, and then
try to create their minor nodes from open context, after the LUA code
has completed.
There are additional zvol use cases that asynchronously own the dataset,
which can cause similar problems. E.g. changing the volmode or snapdev
properties. These are less problematic because they are not recursive
and don't touch datasets that are not involved in the operation, there
is still potential for interference with subsequent operations. In the
future, these cases should be similarly converted to create the zvol
minor node synchronously from open context.
The async tasks of removing and renaming minors do not own the objset,
so they do not have this problem. However, it may make sense to also
convert these operations to happen synchronously from open context, in
the future.
Reviewed-by: Paul Dagnelie <pcd@delphix.com>
Reviewed-by: Prakash Surya <prakash.surya@delphix.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Matthew Ahrens <mahrens@delphix.com>
External-issue: DLPX-65948
Closes#7863Closes#9885
Increase the minimum supported kernel version from 2.6.32 to 3.10.
This removes support for the following Linux enterprise distributions.
Distribution | Kernel | End of Life
---------------- | ------ | -------------
Ubuntu 12.04 LTS | 3.2 | Apr 28, 2017
SLES 11 | 3.0 | Mar 32, 2019
RHEL / CentOS 6 | 2.6.32 | Nov 30, 2020
The following changes were made as part of removing support.
* Updated `configure` to enforce a minimum kernel version as
specified in the META file (Linux-Minimum: 3.10).
configure: error:
*** Cannot build against kernel version 2.6.32.
*** The minimum supported kernel version is 3.10.
* Removed all `configure` kABI checks and matching C code for
interfaces which solely predate the Linux 3.10 kernel.
* Updated all `configure` kABI checks to fail when an interface is
missing which was in the 3.10 kernel up to the latest 5.1 kernel.
Removed the HAVE_* preprocessor defines for these checks and
updated the code to unconditionally use the verified interface.
* Inverted the detection logic in several kABI checks to match
the new interface as it appears in 3.10 and newer and not the
legacy interface.
* Consolidated the following checks in to individual files. Due
the large number of changes in the checks it made sense to handle
this now. It would be desirable to group other related checks in
the same fashion, but this as left as future work.
- config/kernel-blkdev.m4 - Block device kABI checks
- config/kernel-blk-queue.m4 - Block queue kABI checks
- config/kernel-bio.m4 - Bio interface kABI checks
* Removed the kABI checks for sops->nr_cached_objects() and
sops->free_cached_objects(). These interfaces are currently unused.
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#9566
A struct rangelock already exists on FreeBSD. Add a zfs_ prefix as
per our convention to prevent any conflict with existing symbols.
This change is a follow up to 2cc479d0.
Reviewed-by: Matt Ahrens <matt@delphix.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Matt Macy <mmacy@FreeBSD.org>
Closes#9534
This logic is not platform dependent and should reside in the
common code.
Reviewed-by: Igor Kozhukhov <igor@dilos.org>
Reviewed-by: Jorgen Lundman <lundman@lundman.net>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Matt Macy <mmacy@FreeBSD.org>
Closes#9505
A rangelock KPI already exists on FreeBSD. Add a zfs_ prefix as
per our convention to prevent any conflict with existing symbols.
Reviewed-by: Igor Kozhukhov <igor@dilos.org>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Matt Macy <mmacy@FreeBSD.org>
Closes#9402
We've seen cases where after creating a ZVOL, the ZVOL device node in
"/dev" isn't generated after 20 seconds of waiting, which is the point
at which our applications gives up on waiting and reports an error.
The workload when this occurs is to "refresh" 400+ ZVOLs roughly at the
same time, based on a policy set by the user. This refresh operation
will destroy the ZVOL, and re-create it based on a snapshot.
When this occurs, we see many hundreds of entries on the "z_zvol" taskq
(based on inspection of the /proc/spl/taskq-all file). Many of the
entries on the taskq end up in the "zvol_remove_minors_impl" function,
and I've measured the latency of that function:
Function = zvol_remove_minors_impl
msecs : count distribution
0 -> 1 : 0 | |
2 -> 3 : 0 | |
4 -> 7 : 1 | |
8 -> 15 : 0 | |
16 -> 31 : 0 | |
32 -> 63 : 0 | |
64 -> 127 : 1 | |
128 -> 255 : 45 |****************************************|
256 -> 511 : 5 |**** |
That data is from a 10 second sample, using the BCC "funclatency" tool.
As we can see, in this 10 second sample, most calls took 128ms at a
minimum. Thus, some basic math tells us that in any 20 second interval,
we could only process at most about 150 removals, which is much less
than the 400+ that'll occur based on the workload.
As a result of this, and since all ZVOL minor operations will go through
the single threaded "z_zvol" taskq, the latency for creating a single
ZVOL device can be unreasonably large due to other ZVOL activity on the
system. In our case, it's large enough to cause the application to
generate an error and fail the operation.
When profiling the "zvol_remove_minors_impl" function, I saw that most
of the time in the function was spent off-cpu, blocked in the function
"taskq_wait_outstanding". How this works, is "zvol_remove_minors_impl"
will dispatch calls to "zvol_free" using the "system_taskq", and then
the "taskq_wait_outstanding" function is used to wait for all of those
dispatched calls to occur before "zvol_remove_minors_impl" will return.
As far as I can tell, "zvol_remove_minors_impl" doesn't necessarily have
to wait for all calls to "zvol_free" to occur before it returns. Thus,
this change removes the call to "taskq_wait_oustanding", so that calls
to "zvol_free" don't affect the latency of "zvol_remove_minors_impl".
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: John Gallagher <john.gallagher@delphix.com>
Signed-off-by: Prakash Surya <prakash.surya@delphix.com>
Closes#9380
Refactor the zvol in to platform dependent and independent bits.
Reviewed-by: Allan Jude <allanjude@freebsd.org>
Reviewed-by: Jorgen Lundman <lundman@lundman.net>
Reviewed-by: Igor Kozhukhov <igor@dilos.org>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Matt Macy <mmacy@FreeBSD.org>
Closes#9295
