16 Jan, 2015
2 commits
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commit c38d185d4af12e8be63ca4b6745d99449c450f12 upstream.
What we need is the following two guarantees:
* Any thread that observes the effect of the test_and_set_bit() by
__bt_get_word() also observes the preceding addition of 'current'
to the appropriate wait list. This is guaranteed by the semantics
of the spin_unlock() operation performed by prepare_and_wait().
Hence the conversion of test_and_set_bit_lock() into
test_and_set_bit().
* The wait lists are examined by bt_clear() after the tag bit has
been cleared. clear_bit_unlock() guarantees that any thread that
observes that the bit has been cleared also observes the store
operations preceding clear_bit_unlock(). However,
clear_bit_unlock() does not prevent that the wait lists are examined
before that the tag bit is cleared. Hence the addition of a memory
barrier between clear_bit() and the wait list examination.Signed-off-by: Bart Van Assche
Cc: Christoph Hellwig
Cc: Robert Elliott
Cc: Ming Lei
Cc: Alexander Gordeev
Signed-off-by: Jens Axboe
Signed-off-by: Greg Kroah-Hartman -
commit 9e98e9d7cf6e9d2ec1cce45e8d5ccaf3f9b386f3 upstream.
If __bt_get_word() is called with last_tag != 0, if the first
find_next_zero_bit() fails, if after wrap-around the
test_and_set_bit() call fails and find_next_zero_bit() succeeds,
if the next test_and_set_bit() call fails and subsequently
find_next_zero_bit() does not find a zero bit, then another
wrap-around will occur. Avoid this by introducing an additional
local variable.Signed-off-by: Bart Van Assche
Cc: Christoph Hellwig
Cc: Robert Elliott
Cc: Ming Lei
Cc: Alexander Gordeev
Signed-off-by: Jens Axboe
Signed-off-by: Greg Kroah-Hartman
07 Oct, 2014
2 commits
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Eliminate a backwards goto statement from bt_clear_tag().
Signed-off-by: Bart Van Assche
Signed-off-by: Jens Axboe -
We currently divide the queue depth by 4 as our batch wakeup
count, but we split the wakeups over BT_WAIT_QUEUES number of
wait queues. This defaults to 8. If the product of the resulting
batch wake count and BT_WAIT_QUEUES is higher than the device
queue depth, we can get into a situation where a task goes to
sleep waiting for a request, but never gets woken up.Reported-by: Bart Van Assche
Fixes: 4bb659b156996
Cc: stable@kernel.org
Signed-off-by: Jens Axboe
23 Sep, 2014
1 commit
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Don't do a kmalloc from timer to handle timeouts, chances are we could be
under heavy load or similar and thus just miss out on the timeouts.
Fortunately it is very easy to just iterate over all in use tags, and doing
this properly actually cleans up the blk_mq_busy_iter API as well, and
prepares us for the next patch by passing a reserved argument to the
iterator.Signed-off-by: Christoph Hellwig
Signed-off-by: Jens Axboe
18 Jun, 2014
3 commits
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This update fixes few issues in bt_get() function:
- list_empty(&wait.task_list) check is not protected;
- was_empty check is always true which results in *every* thread
entering the loop resets bt_wait_state::wait_cnt counter rather
than every bt->wake_cnt'th thread;- 'bt_wait_state::wait_cnt' counter update is redundant, since
it also gets reset in bt_clear_tag() function;Cc: Christoph Hellwig
Cc: Ming Lei
Cc: Jens Axboe
Signed-off-by: Alexander Gordeev
Signed-off-by: Jens Axboe -
This piece of code in bt_clear_tag() function is racy:
bs = bt_wake_ptr(bt);
if (bs && atomic_dec_and_test(&bs->wait_cnt)) {
atomic_set(&bs->wait_cnt, bt->wake_cnt);
wake_up(&bs->wait);
}Since nothing prevents bt_wake_ptr() from returning the very
same 'bs' address on multiple CPUs, the following scenario is
possible:CPU1 CPU2
---- ----0. bs = bt_wake_ptr(bt); bs = bt_wake_ptr(bt);
1. atomic_dec_and_test(&bs->wait_cnt)
2. atomic_dec_and_test(&bs->wait_cnt)
3. atomic_set(&bs->wait_cnt, bt->wake_cnt);If the decrement in [1] yields zero then for some amount of time
the decrement in [2] results in a negative/overflow value, which
is not expected. The follow-up assignment in [3] overwrites the
invalid value with the batch value (and likely prevents the issue
from being severe) which is still incorrect and should be a lesser.Cc: Ming Lei
Cc: Jens Axboe
Signed-off-by: Alexander Gordeev
Signed-off-by: Jens Axboe -
Fix racy updates of shared blk_mq_bitmap_tags::wake_index
and blk_mq_hw_ctx::wake_index fields.Cc: Ming Lei
Signed-off-by: Alexander Gordeev
Signed-off-by: Jens Axboe
04 Jun, 2014
1 commit
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blk_mq_put_ctx() has to be called before io_schedule() in
bt_get().This patch fixes the problem by taking similar approach from
percpu_ida allocation for the situation.Signed-off-by: Ming Lei
Signed-off-by: Jens Axboe
29 May, 2014
1 commit
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None of the blk-mq files have an explanatory comment at the top
for what that particular file does. Add that and add appropriate
copyright notices as well.Signed-off-by: Jens Axboe
28 May, 2014
1 commit
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The current logic for blocking tag allocation is rather confusing, as we
first allocated and then free again a tag in blk_mq_wait_for_tags, just
to attempt a non-blocking allocation and then repeat if someone else
managed to grab the tag before us.Instead change blk_mq_alloc_request_pinned to simply do a blocking tag
allocation itself and use the request we get back from it.Signed-off-by: Christoph Hellwig
Signed-off-by: Jens Axboe
24 May, 2014
1 commit
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Export the blk-mq in-flight tag iterator for driver consumption.
This is particularly useful in exception paths or SRSI where
in-flight IOs need to be cancelled and/or reissued. The NVMe driver
conversion will use this.Signed-off-by: Sam Bradshaw
Signed-off-by: Matias Bjørling
Signed-off-by: Jens Axboe
21 May, 2014
1 commit
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For request_fn based devices, the block layer exports a 'nr_requests'
file through sysfs to allow adjusting of queue depth on the fly.
Currently this returns -EINVAL for blk-mq, since it's not wired up.
Wire this up for blk-mq, so that it now also always dynamic
adjustments of the allowed queue depth for any given block device
managed by blk-mq.Signed-off-by: Jens Axboe
20 May, 2014
2 commits
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Signed-off-by: Jens Axboe
Conflicts:
block/blk-mq-tag.c -
We will use it for the pending list in blk-mq core as well.
Signed-off-by: Jens Axboe
14 May, 2014
1 commit
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This adds support for active queue tracking, meaning that the
blk-mq tagging maintains a count of active users of a tag set.
This allows us to maintain a notion of fairness between users,
so that we can distribute the tag depth evenly without starving
some users while allowing others to try unfair deep queues.If sharing of a tag set is detected, each hardware queue will
track the depth of its own queue. And if this exceeds the total
depth divided by the number of active queues, the user is actively
throttled down.The active queue count is done lazily to avoid bouncing that data
between submitter and completer. Each hardware queue gets marked
active when it allocates its first tag, and gets marked inactive
when 1) the last tag is cleared, and 2) the queue timeout grace
period has passed.Signed-off-by: Jens Axboe
11 May, 2014
4 commits
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Both nr_cache and nr_tags arn't needed for bitmap tag anymore.
Signed-off-by: Ming Lei
Signed-off-by: Jens Axboe -
The selected tag should be selected at random between 0 and
(depth - 1) with probability 1/depth, instead between 0 and
(depth - 2) with probability 1/(depth - 1).Signed-off-by: Ming Lei
Signed-off-by: Jens Axboe -
The barrier isn't necessary because both atomic_dec_and_test()
and wake_up() implicate one barrier.Signed-off-by: Ming Lei
Signed-off-by: Jens Axboe -
The unlock memory barrier need to order access to req in free
path and clearing tag bit, otherwise either request free path
may see a allocated request, or initialized request in allocate
path might be modified by the ongoing free path.Signed-off-by: Ming Lei
Signed-off-by: Jens Axboe
10 May, 2014
1 commit
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For best performance, spreading tags over multiple cachelines
makes the tagging more efficient on multicore systems. But since
we have 8 * sizeof(unsigned long) tags per cacheline, we don't
always get a nice spread.Attempt to spread the tags over at least 4 cachelines, using fewer
number of bits per unsigned long if we have to. This improves
tagging performance in setups with 32-128 tags. For higher depths,
the spread is the same as before (BITS_PER_LONG tags per cacheline).Signed-off-by: Jens Axboe
09 May, 2014
1 commit
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blk-mq currently uses percpu_ida for tag allocation. But that only
works well if the ratio between tag space and number of CPUs is
sufficiently high. For most devices and systems, that is not the
case. The end result if that we either only utilize the tag space
partially, or we end up attempting to fully exhaust it and run
into lots of lock contention with stealing between CPUs. This is
not optimal.This new tagging scheme is a hybrid bitmap allocator. It uses
two tricks to both be SMP friendly and allow full exhaustion
of the space:1) We cache the last allocated (or freed) tag on a per blk-mq
software context basis. This allows us to limit the space
we have to search. The key element here is not caching it
in the shared tag structure, otherwise we end up dirtying
more shared cache lines on each allocate/free operation.2) The tag space is split into cache line sized groups, and
each context will start off randomly in that space. Even up
to full utilization of the space, this divides the tag users
efficiently into cache line groups, avoiding dirtying the same
one both between allocators and between allocator and freeer.This scheme shows drastically better behaviour, both on small
tag spaces but on large ones as well. It has been tested extensively
to show better performance for all the cases blk-mq cares about.Signed-off-by: Jens Axboe
30 Apr, 2014
1 commit
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blk_mq_wait_for_tags() is only able to wait for "normal" tags,
not reserved tags. Pass in which one we should attempt to get
a tag for, so that waiting for reserved tags will work.Reserved tags are used for internal commands, which are usually
serialized. Hence no waiting generally takes place, but we should
ensure that it actually works if users need that functionality.Signed-off-by: Jens Axboe
16 Apr, 2014
1 commit
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Add a new blk_mq_tag_set structure that gets set up before we initialize
the queue. A single blk_mq_tag_set structure can be shared by multiple
queues.Signed-off-by: Christoph Hellwig
Modular export of blk_mq_{alloc,free}_tagset added by me.
Signed-off-by: Jens Axboe
15 Feb, 2014
1 commit
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Pull block IO fixes from Jens Axboe:
"Second round of updates and fixes for 3.14-rc2. Most of this stuff
has been queued up for a while. The notable exception is the blk-mq
changes, which are naturally a bit more in flux still.The pull request contains:
- Two bug fixes for the new immutable vecs, causing crashes with raid
or swap. From Kent.- Various blk-mq tweaks and fixes from Christoph. A fix for
integrity bio's from Nic.- A few bcache fixes from Kent and Darrick Wong.
- xen-blk{front,back} fixes from David Vrabel, Matt Rushton, Nicolas
Swenson, and Roger Pau Monne.- Fix for a vec miscount with integrity vectors from Martin.
- Minor annotations or fixes from Masanari Iida and Rashika Kheria.
- Tweak to null_blk to do more normal FIFO processing of requests
from Shlomo Pongratz.- Elevator switching bypass fix from Tejun.
- Softlockup in blkdev_issue_discard() fix when !CONFIG_PREEMPT from
me"* 'for-linus' of git://git.kernel.dk/linux-block: (31 commits)
block: add cond_resched() to potentially long running ioctl discard loop
xen-blkback: init persistent_purge_work work_struct
blk-mq: pair blk_mq_start_request / blk_mq_requeue_request
blk-mq: dont assume rq->errors is set when returning an error from ->queue_rq
block: Fix cloning of discard/write same bios
block: Fix type mismatch in ssize_t_blk_mq_tag_sysfs_show
blk-mq: rework flush sequencing logic
null_blk: use blk_complete_request and blk_mq_complete_request
virtio_blk: use blk_mq_complete_request
blk-mq: rework I/O completions
fs: Add prototype declaration to appropriate header file include/linux/bio.h
fs: Mark function as static in fs/bio-integrity.c
block/null_blk: Fix completion processing from LIFO to FIFO
block: Explicitly handle discard/write same segments
block: Fix nr_vecs for inline integrity vectors
blk-mq: Add bio_integrity setup to blk_mq_make_request
blk-mq: initialize sg_reserved_size
blk-mq: handle dma_drain_size
blk-mq: divert __blk_put_request for MQ ops
blk-mq: support at_head inserations for blk_execute_rq
...
11 Feb, 2014
1 commit
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cppcheck detected following format string mismatch.
[blk-mq-tag.c:201]: (warning) %u in format string (no. 1) requires
'unsigned int' but the argument type is 'int'.Change "cpu" from int to unsigned int, because the cpu
never become minus value.Signed-off-by: Masanari Iida
Signed-off-by: Jens Axboe
24 Jan, 2014
1 commit
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This patch changes percpu_ida_alloc() + callers to accept task state
bitmask for prepare_to_wait() for code like target/iscsi that needs
it for interruptible sleep, that is provided in a subsequent patch.It now expects TASK_UNINTERRUPTIBLE when the caller is able to sleep
waiting for a new tag, or TASK_RUNNING when the caller cannot sleep,
and is forced to return a negative value when no tags are available.v2 changes:
- Include blk-mq + tcm_fc + vhost/scsi + target/iscsi changes
- Drop signal_pending_state() call
v3 changes:
- Only call prepare_to_wait() + finish_wait() when != TASK_RUNNING
(PeterZ)Reported-by: Linus Torvalds
Cc: Linus Torvalds
Cc: Ingo Molnar
Cc: Peter Zijlstra
Cc: Jens Axboe
Signed-off-by: Kent Overstreet
Cc: #3.12+
Signed-off-by: Nicholas Bellinger
25 Oct, 2013
1 commit
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Linux currently has two models for block devices:
- The classic request_fn based approach, where drivers use struct
request units for IO. The block layer provides various helper
functionalities to let drivers share code, things like tag
management, timeout handling, queueing, etc.- The "stacked" approach, where a driver squeezes in between the
block layer and IO submitter. Since this bypasses the IO stack,
driver generally have to manage everything themselves.With drivers being written for new high IOPS devices, the classic
request_fn based driver doesn't work well enough. The design dates
back to when both SMP and high IOPS was rare. It has problems with
scaling to bigger machines, and runs into scaling issues even on
smaller machines when you have IOPS in the hundreds of thousands
per device.The stacked approach is then most often selected as the model
for the driver. But this means that everybody has to re-invent
everything, and along with that we get all the problems again
that the shared approach solved.This commit introduces blk-mq, block multi queue support. The
design is centered around per-cpu queues for queueing IO, which
then funnel down into x number of hardware submission queues.
We might have a 1:1 mapping between the two, or it might be
an N:M mapping. That all depends on what the hardware supports.blk-mq provides various helper functions, which include:
- Scalable support for request tagging. Most devices need to
be able to uniquely identify a request both in the driver and
to the hardware. The tagging uses per-cpu caches for freed
tags, to enable cache hot reuse.- Timeout handling without tracking request on a per-device
basis. Basically the driver should be able to get a notification,
if a request happens to fail.- Optional support for non 1:1 mappings between issue and
submission queues. blk-mq can redirect IO completions to the
desired location.- Support for per-request payloads. Drivers almost always need
to associate a request structure with some driver private
command structure. Drivers can tell blk-mq this at init time,
and then any request handed to the driver will have the
required size of memory associated with it.- Support for merging of IO, and plugging. The stacked model
gets neither of these. Even for high IOPS devices, merging
sequential IO reduces per-command overhead and thus
increases bandwidth.For now, this is provided as a potential 3rd queueing model, with
the hope being that, as it matures, it can replace both the classic
and stacked model. That would get us back to having just 1 real
model for block devices, leaving the stacked approach to dm/md
devices (as it was originally intended).Contributions in this patch from the following people:
Shaohua Li
Alexander Gordeev
Christoph Hellwig
Mike Christie
Matias Bjorling
Jeff MoyerAcked-by: Christoph Hellwig
Signed-off-by: Jens Axboe
