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>
In case a device has three tags available we still reserve two of them
for sync IO. That leaves only a single tag for async IO such as
writeback from flusher thread which results in poor performance.
Allow async IO to consume two tags in case queue has three tag availabe
to get a decent async write performance.
This patch improves streaming write performance on a machine with such disk
from ~21 MB/s to ~52 MB/s. Also postmark throughput in presence of
streaming writer improves from 8 to 12 transactions per second so sync
IO doesn't seem to be harmed in presence of heavy async writer.
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Code in blkdev.c moves a device inode to default_backing_dev_info when
the last reference to the device is put and moves the device inode back
to its bdi when the first reference is acquired. This includes moving to
wb.b_dirty list if the device inode is dirty. The code however doesn't
setup timer to wake corresponding flusher thread and while wb.b_dirty
list is non-empty __mark_inode_dirty() will not set it up either. Thus
periodic writeback is effectively disabled until a sync(2) call which can
lead to unexpected data loss in case of crash or power failure.
Fix the problem by setting up a timer for periodic writeback in case we
add the first dirty inode to wb.b_dirty list in bdev_inode_switch_bdi().
Reported-by: Bert De Jonghe <Bert.DeJonghe@amplidata.com>
CC: stable@vger.kernel.org # >= 3.0
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
With the recent updates, blk-throttle is finally ready for proper
hierarchy support. Dispatching now honors service_queue->parent_sq
and propagates correctly. The only thing missing is setting
->parent_sq correctly so that throtl_grp hierarchy matches the cgroup
hierarchy.
This patch updates throtl_pd_init() such that service_queues form the
same hierarchy as the cgroup hierarchy if sane_behavior is enabled.
As this concludes proper hierarchy support for blkcg, the shameful
.broken_hierarchy tag is removed from blkio_subsys.
v2: Updated blkio-controller.txt as suggested by Vivek.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Vivek Goyal <vgoyal@redhat.com>
Cc: Li Zefan <lizefan@huawei.com>
blk_throtl_bio() has a quick exit path for throtl_grps without limits
configured. It looks at the bps and iops limits and if both are not
configured, the bio is issued immediately. While this is correct in
the current flat hierarchy as each throtl_grp behaves completely
independently, it would become wrong in proper hierarchy mode. A
group without any limits could still be limited by one of its
ancestors and bio's queued for such group should not bypass
blk-throtl.
As having a quick bypass mechanism is beneficial, this patch
reimplements the mechanism such that it's correct even with proper
hierarchy. throtl_grp->has_rules[] is added. These booleans are
updated for the whole subtree whenever a config is updated so that
has_rules[] of the whole subtree stays synchronized. They're also
updated when a new throtl_grp comes online so that it can't escape the
limits of its ancestors.
As no throtl_grp has another throtl_grp as parent now, this patch
doesn't yet make any behavior differences.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Vivek Goyal <vgoyal@redhat.com>
With the planned proper hierarchy support, a bio will climb up the
tree before actually being dispatched. This makes sure bio is also
subjected to parent's throttling limits, if any.
It might happen that parent is idle and when bio is transferred to
parent, a new slice starts fresh. But that is incorrect as parents
wait time should have started when bio was queued in child group and
causes IOs to be throttled more than configured as they climb the
hierarchy.
Given the fact that we have not written hierarchical algorithm in a
way where child's and parents time slices are synchronized, we
transfer the child's start time to parent if parent was idling. If
parent was busy doing dispatch of other bios all this while, this is
not an issue.
Child's slice start time is passed to parent. Parent looks at its
last expired slice start time. If child's start time is after parents
old start time, that means parent had been idle and after parent
went idle, child had an IO queued. So use child's start time as
parent start time.
If parent's start time is after child's start time, that means,
when IO got queued in child group, parent was not idle. But later
it dispatched some IO, its slice got trimmed and then it went idle.
After a while child's request got shifted in parent group. In this
case use parent's old start time as new start time as that's the
duration of slice we did not use.
This logic is far from perfect as if there are multiple childs
then first child transferring the bio decides the start time while
a bio might have queued up even earlier in other child, which is
yet to be transferred up to parent. In that case we will lose
time and bandwidth in parent. This patch is just an approximation
to make situation somewhat better.
Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
With flat hierarchy, there's only single level of dispatching
happening and fairness beyond that point is the responsibility of the
rest of the block layer and driver, which usually works out okay;
however, with the planned hierarchy support,
service_queue->bio_lists[] can be filled up by bios from a single
source. While the limits would still be honored, it'd be very easy to
starve IOs from siblings or children.
To avoid such starvation, this patch implements throtl_qnode and
converts service_queue->bio_lists[] to lists of per-source qnodes
which in turn contains the bio's. For example, when a bio is
dispatched from a child group, the bio doesn't get queued on
->bio_lists[] directly but it first gets queued on the group's qnode
which in turn gets queued on service_queue->queued[]. When
dispatching for the upper level, the ->queued[] list is consumed in
round-robing order so that the dispatch windows is consumed fairly by
all IO sources.
There are two ways a bio can come to a throtl_grp - directly queued to
the group or dispatched from a child. For the former
throtl_grp->qnode_on_self[rw] is used. For the latter, the child's
->qnode_on_parent[rw].
Note that this means that the child which is contributing a bio to its
parent should stay pinned until all its bios are dispatched to its
grand-parent. This patch moves blkg refcnting from bio add/remove
spots to qnode activation/deactivation so that the blkg containing an
active qnode is always pinned. As child pins the parent, this is
sufficient for keeping the relevant sub-tree pinned while bios are in
flight.
The starvation issue was spotted by Vivek Goyal.
v2: The original patch used the same throtl_grp->qnode_on_self/parent
for reads and writes causing RWs to be queued incorrectly if there
already are outstanding IOs in the other direction. They should
be throtl_grp->qnode_on_self/parent[2] so that READs and WRITEs
can use different qnodes. Spotted by Vivek Goyal.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Vivek Goyal <vgoyal@redhat.com>
throtl_pending_timer_fn() currently assumes that the parent_sq is the
top level one and the bio's dispatched are ready to be issued;
however, this assumption will be wrong with proper hierarchy support.
This patch makes the following changes to make
throtl_pending_timer_fn() ready for hiearchy.
* If the parent_sq isn't the top-level one, update the parent
throtl_grp's dispatch time and schedule the next dispatch as
necessary. If the parent's dispatch time is now, repeat the
function for the parent throtl_grp.
* If the parent_sq is the top-level one, kick issue work_item as
before.
* The debug message printed by throtl_log() now prints out the
service_queue's nr_queued[] instead of the total nr_queued as the
latter becomes uninteresting and misleading with hierarchical
dispatch.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Vivek Goyal <vgoyal@redhat.com>
tg_dispatch_one_bio() currently assumes that the parent_sq is the top
level one and the bio being dispatched is ready to be issued; however,
this assumption will be wrong with proper hierarchy support. This
patch makes the following changes to make tg_dispatch_on_bio() ready
for hiearchy.
* throtl_data->nr_queued[] is incremented in blk_throtl_bio() instead
of throtl_add_bio_tg() so that throtl_add_bio_tg() can be used to
transfer a bio from a child tg to its parent.
* tg_dispatch_one_bio() is updated to distinguish whether its parent
is another throtl_grp or the throtl_data. If former, the bio is
transferred to the parent throtl_grp using throtl_add_bio_tg(). If
latter, the bio is ready to be issued and put on the top-level
service_queue's bio_lists[] and throtl_data->nr_queued is
decremented.
As all throtl_grps currently have the top level service_queue as their
->parent_sq, this patch in itself doesn't make any behavior
difference.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Vivek Goyal <vgoyal@redhat.com>
Currently, blk_throtl_bio() issues the passed in bio directly if it's
within limits of its associated tg (throtl_grp). This behavior
becomes incorrect with hierarchy support as the bio should be
accounted to and throttled by the ancestor throtl_grps too.
This patch makes the direct issue path of blk_throtl_bio() to loop
until it reaches the top-level service_queue or gets throttled. If
the former, the bio can be issued directly; otherwise, it gets queued
at the first layer it was above limits.
As tg->parent_sq is always the top-level service queue currently, this
patch in itself doesn't make any behavior differences.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Vivek Goyal <vgoyal@redhat.com>
The current blk_throtl_drain() assumes that all active throtl_grps are
queued on throtl_data->service_queue, which won't be true once
hierarchy support is implemented.
This patch makes blk_throtl_drain() perform post-order walk of the
blkg hierarchy draining each associated throtl_grp, which guarantees
that all bios will eventually be pushed to the top-level service_queue
in throtl_data.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Vivek Goyal <vgoyal@redhat.com>
Currently, blk_throtl_dispatch_work_fn() is responsible for both
dispatching bio's from throtl_grp's according to their limits and then
issuing the dispatched bios.
This patch moves the dispatch part to throtl_pending_timer_fn() so
that the work item is kicked iff there are bio's to issue. This is to
avoid work item execution at each step when hierarchy support is
enabled. bio's will be dispatched towards the top-level service_queue
from the timers at each layer and the work item will only be used to
issue the bio's which reached the top-level service_queue.
While fetching bio's to issue from bio_lists[],
blk_throtl_dispatch_work_fn() fetches all READs before WRITEs. While
the original code also dispatched READs first, if multiple throtl_grps
are dispatched on the same run, WRITEs from throtl_grp which is
dispatched first would precede READs from throtl_grps which are
dispatched later. While this is a behavior change, given that the
previous code already prioritized READs and block layer generally
prioritizes and segregates READs from WRITEs, this isn't likely to
make any noticeable differences.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Vivek Goyal <vgoyal@redhat.com>
throtl_select_dispatch() only dispatches throtl_quantum bios on each
invocation. blk_throtl_dispatch_work_fn() in turn depends on
throtl_schedule_next_dispatch() scheduling the next dispatch window
immediately so that undue delays aren't incurred. This effectively
chains multiple dispatch work item executions back-to-back when there
are more than throtl_quantum bios to dispatch on a given tick.
There is no reason to finish the current work item just to repeat it
immediately. This patch makes throtl_schedule_next_dispatch() return
%false without doing anything if the current dispatch window is still
open and updates blk_throtl_dispatch_work_fn() repeat dispatching
after cpu_relax() on %false return.
This change will help implementing hierarchy support as dispatching
will be done from pending_timer and immediate reschedule of timer
function isn't supported and doesn't make much sense.
While this patch changes how dispatch behaves when there are more than
throtl_quantum bios to dispatch on a single tick, the behavior change
is immaterial.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Vivek Goyal <vgoyal@redhat.com>
Currently, throtl_data->dispatch_work is a delayed_work item which
handles both delayed dispatch and issuing bios. The two tasks will be
separated to support proper hierarchy. To prepare for that, this
patch separates out the timer into throtl_service_queue->pending_timer
from throtl_data->dispatch_work and make the latter a work_struct.
* As the timer is now per-service_queue, it's initialized and
del_sync'd as its corresponding service_queue is created and
destroyed. The timer, when triggered, simply schedules
throtl_data->dispathc_work for execution.
* throtl_schedule_delayed_work() is renamed to
throtl_schedule_pending_timer() and takes @sq and @expires now.
* Simiarly, throtl_schedule_next_dispatch() now takes @sq, which
should be the parent_sq of the service_queue which just got a new
bio or updated. As the parent_sq is always the top-level
service_queue now, this doesn't change anything at this point.
This patch doesn't introduce any behavior differences.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Vivek Goyal <vgoyal@redhat.com>
With proper hierarchy support, a bio can be dispatched multiple times
until it reaches the top-level service_queue and we don't want to
update dispatch stats at each step. They are local stats and will be
kept local. If recursive stats are necessary, they should be
implemented separately and definitely not by updating counters
recursively on each dispatch.
This patch moves REQ_THROTTLED setting to throtl_charge_bio() and gate
stats update with it so that dispatch stats are updated only on the
first time the bio is charged to a throtl_grp, which will always be
the throtl_grp the bio was originally queued to.
This means that REQ_THROTTLED would be set even for bios which don't
get throttled. As we don't want bios to leave blk-throtl with the
flag set, move REQ_THROTLLED clearing to the end of blk_throtl_bio()
and clear if the bio is being issued directly.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Vivek Goyal <vgoyal@redhat.com>
Now that both throtl_data and throtl_grp embed throtl_service_queue,
we can unify throtl_log() and throtl_log_tg().
* sq_to_tg() is added. This returns the throtl_grp a service_queue is
embedded in. If the service_queue is the top-level one embedded in
throtl_data, NULL is returned.
* sq_to_td() is added. A service_queue is always associated with a
throtl_data. This function finds the associated td and returns it.
* throtl_log() is updated to take throtl_service_queue instead of
throtl_data. If the service_queue is one embedded in throtl_grp, it
prints the same header as throtl_log_tg() did. If it's one embedded
in throtl_data, it behaves the same as before. This renders
throtl_log_tg() unnecessary. Removed.
This change is necessary for hierarchy support as we're gonna be using
the same code paths to dispatch bios to intermediate service_queues
embedded in throtl_grps and the top-level service_queue embedded in
throtl_data.
This patch doesn't make any behavior changes.
v2: throtl_log() didn't print a space after blkg path. Updated so
that it prints a space after throtl_grp path. Spotted by Vivek.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Vivek Goyal <vgoyal@redhat.com>
To prepare for hierarchy support, this patch adds
throtl_service_queue->service_sq which points to the arent
service_queue. Currently, for all service_queues embedded in
throtl_grps, it points to throtl_data->service_queue. As
throtl_data->service_queue doesn't have a parent its parent_sq is set
to NULL.
There are a number of functions which take both throtl_grp *tg and
throtl_service_queue *parent_sq. With this patch, the parent
service_queue can be determined from @tg and the @parent_sq arguments
are removed.
This patch doesn't make any behavior differences.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Vivek Goyal <vgoyal@redhat.com>
When blk_throtl_bio() wants to queue a bio to a tg (throtl_grp), it
avoids invoking tg_update_disptime() and
throtl_schedule_next_dispatch() if the tg already has bios queued in
that direction. As a new bio is appeneded after the existing ones, it
can't change the tg's next dispatch time or the parent's dispatch
schedule.
This optimization is currently open coded in blk_throtl_bio().
Whether the target biolist was occupied was recorded in a local
variable and later used to skip disptime update. This patch moves
generalizes it so that throtl_add_bio_tg() sets a new flag
THROTL_TG_WAS_EMPTY if the biolist was empty before the new bio was
added. tg_update_disptime() clears the flag automatically.
blk_throtl_bio() is updated to simply test the flag before updating
disptime.
This patch doesn't make any functional differences now but will enable
using the same optimization for recursive dispatch.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Vivek Goyal <vgoyal@redhat.com>
throtl_service_queues will eventually form a tree which is anchored at
throtl_data->service_queue and queue bios will climb the tree to the
top service_queue to be executed.
This patch makes the dispatch paths in blk_throtl_dispatch_work_fn()
and blk_throtl_drain() to dispatch bios to
throtl_data->service_queue.bio_lists[] instead of the on-stack
bio_lists. This will keep the final dispatch to the top level
service_queue share the same mechanism as dispatches through the rest
of the hierarchy.
As bio's should be issued in a sleepable context,
blk_throtl_dispatch_work_fn() transfers all dispatched bio's from the
service_queue bio_lists[] into an onstack one before dropping
queue_lock and issuing the bio's.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Vivek Goyal <vgoyal@redhat.com>
throtl_service_queues will eventually form a tree which is anchored at
throtl_data->service_queue and queue bios will climb the tree to the
top service_queue to be executed.
This patch moves bio_lists[] and nr_queued[] from throtl_grp to its
service_queue to prepare for that. As currently only the
throtl_data->service_queue is in use, this patch just ends up moving
throtl_grp->bio_lists[] and ->nr_queued[] to
throtl_grp->service_queue.bio_lists[] and ->nr_queued[] without making
any functional differences.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Vivek Goyal <vgoyal@redhat.com>
Currently, there's single service_queue per queue -
throtl_data->service_queue. All active throtl_grp's are queued on the
queue and dispatched according to their limits. To support hierarchy,
this will be expanded such that active throtl_grp's form a tree
anchored at throtl_data->service_queue and chained through each
intermediate throtl_grp's service_queue.
This patch adds throtl_grp->service_queue to prepare for hierarchy
support. The initialization function - throtl_service_queue_init() -
is added and replaces the macro initializer. The newly added
tg->service_queue isn't used yet. Following patches will do.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Vivek Goyal <vgoyal@redhat.com>
throtl_service_queue will be the building block of hierarchy support
and will form a tree. This patch updates its usages as arguments to
reduce confusion.
* When a service queue is used as the parent role - the host of the
rbtree - use @parent_sq instead of @sq.
* For functions taking both @tg and @parent_sq, reorder them so that
the order is (@tg, @parent_sq) not the other way around. This makes
the code follow the usual convention of specifying the primary
target of the operation as the first argument.
This patch doesn't make any functional differences.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Vivek Goyal <vgoyal@redhat.com>
throtl_service_queue will be used as the basic block to implement
hierarchy support. Pass around throtl_service_queue *sq instead of
throtl_data *td in the following functions which will be used across
multiple levels of hierarchy.
* [__]throtl_enqueue/dequeue_tg()
* throtl_add_bio_tg()
* tg_update_disptime()
* throtl_select_dispatch()
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Vivek Goyal <vgoyal@redhat.com>
Add throtl_grp->td so that the td (throtl_data) a given tg
(throtl_grp) belongs to can be determined, and remove @td argument
from functions which take both @td and @tg as the former now can be
determined from the latter.
This generally simplifies the code and removes a number of cases where
@td is passed as an argument without being actually used. This will
also help hierarchy support implementation.
While at it, in multi-line conditions, move the logical operators
leading broken lines to the end of the previous line.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Vivek Goyal <vgoyal@redhat.com>
blk-throttle is still using function-defining macros to define flag
handling functions, which went out style at least a decade ago.
Just define the flag as bitmask and use direct bit operations.
This patch doesn't make any functional changes.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Vivek Goyal <vgoyal@redhat.com>
Jianpeng Ma
Jan Kara
Tejun Heo
Vivek Goyal