This patch makes sure we always allocate requests in the core blk-mq
code and use a common prepare_request method to initialize them for
both mq I/O schedulers. For Kyber and additional limit_depth method
is added that is called before allocating the request.
Also because none of the intializations can really fail the new method
does not return an error - instead the bfq finish method is hardened
to deal with the no-IOC case.
Last but not least this removes the abuse of RQF_QUEUE by the blk-mq
scheduling code as RQF_ELFPRIV is all that is needed now.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
gcc 7.1 reports the following warning:
block/elevator.c: In function ‘elv_register’:
block/elevator.c:898:5: warning: ‘snprintf’ output may be truncated before the last format character [-Wformat-truncation=]
"%s_io_cq", e->elevator_name);
^~~~~~~~~~
block/elevator.c:897:3: note: ‘snprintf’ output between 7 and 22 bytes into a destination of size 21
snprintf(e->icq_cache_name, sizeof(e->icq_cache_name),
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
"%s_io_cq", e->elevator_name);
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The bug is that the name of the icq_cache is 6 characters longer than
the elevator name, but only ELV_NAME_MAX + 5 characters were reserved
for it --- so in the case of a maximum-length elevator name, the 'q'
character in "_io_cq" would be truncated by snprintf(). Fix it by
reserving ELV_NAME_MAX + 6 characters instead.
Signed-off-by: Eric Biggers <ebiggers@google.com>
Reviewed-by: Bart Van Assche <Bart.VanAssche@sandisk.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
This provides the infrastructure for schedulers to expose their internal
state through debugfs. We add a list of queue attributes and a list of
hctx attributes to struct elevator_type and wire them up when switching
schedulers.
Signed-off-by: Omar Sandoval <osandov@fb.com>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Add missing seq_file.h header in blk-mq-debugfs.h
Signed-off-by: Jens Axboe <axboe@fb.com>
Since commit 8425339492 ("remove the mg_disk driver") removed the
only caller of elevator_change(), also remove the elevator_change()
function itself.
Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Markus Trippelsdorf <markus@trippelsdorf.de>
Signed-off-by: Jens Axboe <axboe@fb.com>
Currently, this callback is called right after put_request() and has no
distinguishable purpose. Instead, let's call it before put_request() as
soon as I/O has completed on the request, before we account it in
blk-stat. With this, Kyber can enable stats when it sees a latency
outlier and make sure the outlier gets accounted.
Signed-off-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
Schedulers need to be informed when a hardware queue is added or removed
at runtime so they can allocate/free per-hardware queue data. So,
replace the blk_mq_sched_init_hctx_data() helper, which only makes sense
at init time, with .init_hctx() and .exit_hctx() hooks.
Signed-off-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
In elevator_switch(), if blk_mq_init_sched() fails, we attempt to fall
back to the original scheduler. However, at this point, we've already
torn down the original scheduler's tags, so this causes a crash. Doing
the fallback like the legacy elevator path is much harder for mq, so fix
it by just falling back to none, instead.
Signed-off-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
bio is used in bfq-mq's get_rq_priv, to get the request group. We could
pass directly the group here, but I thought that passing the bio was
more general, giving the possibility to get other pieces of information
if needed.
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Jens Axboe <axboe@fb.com>
Add a new merge strategy that merges discard bios into a request until the
maximum number of discard ranges (or the maximum discard size) is reached
from the plug merging code. I/O scheduler merging is not wired up yet
but might also be useful, although not for fast devices like NVMe which
are the only user for now.
Note that for now we don't support limiting the size of each discard range,
but if needed that can be added later.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@fb.com>
Switch these constants to an enum, and make let the compiler ensure that
all callers of blk_try_merge and elv_merge handle all potential values.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@fb.com>
When we invoke dispatch_requests(), the scheduler empties everything
into the passed in list. This isn't always a good thing, since it
means that we remove items that we could have potentially merged
with.
Change the function to dispatch single requests at the time. If
we do that, we can backoff exactly at the point where the device
can't consume more IO, and leave the rest with the scheduler for
better merging and future dispatch decision making.
Signed-off-by: Jens Axboe <axboe@fb.com>
Reviewed-by: Omar Sandoval <osandov@fb.com>
Tested-by: Hannes Reinecke <hare@suse.com>
This adds a set of hooks that intercepts the blk-mq path of
allocating/inserting/issuing/completing requests, allowing
us to develop a scheduler within that framework.
We reuse the existing elevator scheduler API on the registration
side, but augment that with the scheduler flagging support for
the blk-mq interfce, and with a separate set of ops hooks for MQ
devices.
We split driver and scheduler tags, so we can run the scheduling
independently of device queue depth.
Signed-off-by: Jens Axboe <axboe@fb.com>
Reviewed-by: Bart Van Assche <bart.vanassche@sandisk.com>
Reviewed-by: Omar Sandoval <osandov@fb.com>
Prep patch for adding MQ ops as well, since doing anon unions with
named initializers doesn't work on older compilers.
Signed-off-by: Jens Axboe <axboe@fb.com>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: Bart Van Assche <bart.vanassche@sandisk.com>
Reviewed-by: Omar Sandoval <osandov@fb.com>
Now that we don't need the common flags to overflow outside the range
of a 32-bit type we can encode them the same way for both the bio and
request fields. This in addition allows us to place the operation
first (and make some room for more ops while we're at it) and to
stop having to shift around the operation values.
In addition this allows passing around only one value in the block layer
instead of two (and eventuall also in the file systems, but we can do
that later) and thus clean up a lot of code.
Last but not least this allows decreasing the size of the cmd_flags
field in struct request to 32-bits. Various functions passing this
value could also be updated, but I'd like to avoid the churn for now.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@fb.com>
Before merging a bio into an existing request, io scheduler is called to
get its approval first. However, the requests that come from a plug
flush may get merged by block layer without consulting with io
scheduler.
In case of CFQ, this can cause fairness problems. For instance, if a
request gets merged into a low weight cgroup's request, high weight cgroup
now will depend on low weight cgroup to get scheduled. If high weigt cgroup
needs that io request to complete before submitting more requests, then it
will also lose its timeslice.
Following script demonstrates the problem. Group g1 has a low weight, g2
and g3 have equal high weights but g2's requests are adjacent to g1's
requests so they are subject to merging. Due to these merges, g2 gets
poor disk time allocation.
cat > cfq-merge-repro.sh << "EOF"
#!/bin/bash
set -e
IO_ROOT=/mnt-cgroup/io
mkdir -p $IO_ROOT
if ! mount | grep -qw $IO_ROOT; then
mount -t cgroup none -oblkio $IO_ROOT
fi
cd $IO_ROOT
for i in g1 g2 g3; do
if [ -d $i ]; then
rmdir $i
fi
done
mkdir g1 && echo 10 > g1/blkio.weight
mkdir g2 && echo 495 > g2/blkio.weight
mkdir g3 && echo 495 > g3/blkio.weight
RUNTIME=10
(echo $BASHPID > g1/cgroup.procs &&
fio --readonly --name name1 --filename /dev/sdb \
--rw read --size 64k --bs 64k --time_based \
--runtime=$RUNTIME --offset=0k &> /dev/null)&
(echo $BASHPID > g2/cgroup.procs &&
fio --readonly --name name1 --filename /dev/sdb \
--rw read --size 64k --bs 64k --time_based \
--runtime=$RUNTIME --offset=64k &> /dev/null)&
(echo $BASHPID > g3/cgroup.procs &&
fio --readonly --name name1 --filename /dev/sdb \
--rw read --size 64k --bs 64k --time_based \
--runtime=$RUNTIME --offset=256k &> /dev/null)&
sleep $((RUNTIME+1))
for i in g1 g2 g3; do
echo ---- $i ----
cat $i/blkio.time
done
EOF
# ./cfq-merge-repro.sh
---- g1 ----
8:16 162
---- g2 ----
8:16 165
---- g3 ----
8:16 686
After applying the patch:
# ./cfq-merge-repro.sh
---- g1 ----
8:16 90
---- g2 ----
8:16 445
---- g3 ----
8:16 471
Signed-off-by: Tahsin Erdogan <tahsin@google.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
This patch converts the elevator code to use separate variables
for the operation and flags, and to check req_op for the REQ_OP.
Signed-off-by: Mike Christie <mchristi@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
A previous commit wanted to make CFQ default to IOPS mode on
non-rotational storage, however it did so when the queue was
initialized and the non-rotational flag is only set later on
in the probe.
Add an elevator hook that gets called off the add_disk() path,
at that point we know that feature probing has finished, and
we can reliably check for the various flags that drivers can
set.
Fixes: 41c0126b ("block: Make CFQ default to IOPS mode on SSDs")
Tested-by: Romain Francoise <romain@orebokech.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
This reverts commit b5097e956a.
The original commit is buggy, we do use the registration functions
at runtime, for instance when loading IO schedulers through sysfs.
Reported-by: Damien Wyart <damien.wyart@gmail.com>
elv_abort_queue has no callers, and blk_abort_flushes is only called by
elv_abort_queue.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@fb.com>
elv_register is only called by elevator init functions:
__init cfq_init
__init deadline_init
__init noop_init
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Fabian Frederick <fabf@skynet.be>
Signed-off-by: Jens Axboe <axboe@fb.com>
rq_fifo_clear() reset the csd.list through INIT_LIST_HEAD for no clear
purpose. The csd.list doesn't need to be initialized as a list head
because it's only ever used as a list node.
Lets remove this useless initialization.
Reviewed-by: Jan Kara <jack@suse.cz>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jan Kara <jack@suse.cz>
Cc: Jens Axboe <axboe@fb.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
Block layer currently abuses rq->csd.list.next for storing fifo_time.
That is a terrible hack and completely unnecessary as well. Union
achieves the same space saving in a cleaner way.
Signed-off-by: Jan Kara <jack@suse.cz>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jens Axboe <axboe@fb.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
There's a race between elevator switching and normal io operation.
Because the allocation of struct elevator_queue and struct elevator_data
don't in a atomic operation.So there are have chance to use NULL
->elevator_data.
For example:
Thread A: Thread B
blk_queu_bio elevator_switch
spin_lock_irq(q->queue_block) elevator_alloc
elv_merge elevator_init_fn
Because call elevator_alloc, it can't hold queue_lock and the
->elevator_data is NULL.So at the same time, threadA call elv_merge and
nedd some info of elevator_data.So the crash happened.
Move the elevator_alloc into func elevator_init_fn, it make the
operations in a atomic operation.
Using the follow method can easy reproduce this bug
1:dd if=/dev/sdb of=/dev/null
2:while true;do echo noop > scheduler;echo deadline > scheduler;done
The test method also use this method.
Signed-off-by: Jianpeng Ma <majianpeng@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
