bfqd->bfq_wr_max_time is set to 0 in bfq_init_queue and is never changed.
It is only used in bfq_wr_duration when bfq_wr_max_time > 0 which never
meets, so bfqd->bfq_wr_max_time is not used actually. Just remove it.
Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20230116095153.3810101-9-shikemeng@huaweicloud.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
The main service scheme of BFQ for sync I/O is serving one sync
bfq_queue at a time, for a while. In particular, BFQ enforces this
scheme when it deems the latter necessary to boost throughput or
to preserve service guarantees. Unfortunately, when BFQ enforces
this policy, only one actuator at a time gets served for a while,
because each bfq_queue contains I/O only for one actuator. The
other actuators may remain underutilized.
Actually, BFQ may serve (inject) extra I/O, taken from other
bfq_queues, in parallel with that of the in-service queue. This
injection mechanism may provide the ground for dealing also with
the above actuator-underutilization problem. Yet BFQ does not take
the actuator load into account when choosing which queue to pick
extra I/O from. In addition, BFQ may happen to inject extra I/O
only when the in-service queue is temporarily empty.
In view of these facts, this commit extends the
injection mechanism in such a way that the latter:
(1) takes into account also the actuator load;
(2) checks such a load on each dispatch, and injects I/O for an
underutilized actuator, if there is one and there is I/O for it.
To perform the check in (2), this commit introduces a load
threshold, currently set to 4. A linear scan of each actuator is
performed, until an actuator is found for which the following two
conditions hold: the load of the actuator is below the threshold,
and there is at least one non-in-service queue that contains I/O
for that actuator. If such a pair (actuator, queue) is found, then
the head request of that queue is returned for dispatch, instead
of the head request of the in-service queue.
We have set the threshold, empirically, to the minimum possible
value for which an actuator is fully utilized, or close to be
fully utilized. By doing so, injected I/O 'steals' as few
drive-queue slots as possibile to the in-service queue. This
reduces as much as possible the probability that the service of
I/O from the in-service bfq_queue gets delayed because of slot
exhaustion, i.e., because all the slots of the drive queue are
filled with I/O injected from other queues (NCQ provides for 32
slots).
This new mechanism also counters actuator underutilization in the
case of asymmetric configurations of bfq_queues. Namely if there
are few bfq_queues containing I/O for some actuators and many
bfq_queues containing I/O for other actuators. Or if the
bfq_queues containing I/O for some actuators have lower weights
than the other bfq_queues.
Reviewed-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Davide Zini <davidezini2@gmail.com>
Link: https://lore.kernel.org/r/20230103145503.71712-8-paolo.valente@linaro.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This patch implements the code to gather the content of the
independent_access_ranges structure from the request_queue and copy
it into the queue's bfq_data. This copy is done at queue initialization.
We copy the access ranges into the bfq_data to avoid taking the queue
lock each time we access the ranges.
This implementation, however, puts a limit to the maximum independent
ranges supported by the scheduler. Such a limit is equal to the constant
BFQ_MAX_ACTUATORS. This limit was placed to avoid the allocation of
dynamic memory.
Reviewed-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
Co-developed-by: Rory Chen <rory.c.chen@seagate.com>
Signed-off-by: Rory Chen <rory.c.chen@seagate.com>
Signed-off-by: Federico Gavioli <f.gavioli97@gmail.com>
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Link: https://lore.kernel.org/r/20230103145503.71712-7-paolo.valente@linaro.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Similarly to sync bfq_queues, also async bfq_queues need to be split
on a per-actuator basis.
Reviewed-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Davide Zini <davidezini2@gmail.com>
Link: https://lore.kernel.org/r/20230103145503.71712-6-paolo.valente@linaro.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
When a bfq_queue Q is merged with another queue, several pieces of
information are saved about Q. These pieces are stored in the
bfqq_data field in the bfq_io_cq data structure of the process
associated with Q.
Yet, with a multi-actuator drive, a process may get associated with
multiple bfq_queues: one queue for each of the N actuators. Each of
these queues may undergo a merge. So, the bfq_io_cq data structure
must be able to accommodate the above information for N queues.
This commit solves this problem by turning the bfqq_data scalar field
into an array of N elements (and by changing code so as to handle
this array).
This solution is written under the assumption that bfq_queues
associated with different actuators cannot be cross-merged. This
assumption holds naturally with basic queue merging: the latter is
triggered by spatial locality, and sectors for different actuators are
not close to each other (apart from the corner case of the last
sectors served by a given actuator and the first sectors served by the
next actuator). As for stable cross-merging, the assumption here is
that it is disabled.
Reviewed-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
Signed-off-by: Gabriele Felici <felicigb@gmail.com>
Signed-off-by: Gianmarco Lusvardi <glusvardi@posteo.net>
Signed-off-by: Giulio Barabino <giuliobarabino99@gmail.com>
Signed-off-by: Emiliano Maccaferri <inbox@emilianomaccaferri.com>
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Link: https://lore.kernel.org/r/20230103145503.71712-5-paolo.valente@linaro.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
With a multi-actuator drive, a process may get associated with multiple
bfq_queues: one queue for each of the N actuators. So, the bfq_io_cq
data structure must be able to accommodate its per-queue persistent
information for N queues. Currently it stores this information for
just one queue, in several scalar fields.
This is a preparatory commit for moving to accommodating persistent
information for N queues. In particular, this commit packs all the
above scalar fields into a single data structure. Then there is now
only one field, in bfq_io_cq, that stores all the above information. This
scalar field will then be turned into an array by a following commit.
Suggested-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
Reviewed-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
Signed-off-by: Gianmarco Lusvardi <glusvardi@posteo.net>
Signed-off-by: Giulio Barabino <giuliobarabino99@gmail.com>
Signed-off-by: Emiliano Maccaferri <inbox@emilianomaccaferri.com>
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Link: https://lore.kernel.org/r/20230103145503.71712-4-paolo.valente@linaro.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Single-LUN multi-actuator SCSI drives, as well as all multi-actuator
SATA drives appear as a single device to the I/O subsystem [1]. Yet
they address commands to different actuators internally, as a function
of Logical Block Addressing (LBAs). A given sector is reachable by
only one of the actuators. For example, Seagate’s Serial Advanced
Technology Attachment (SATA) version contains two actuators and maps
the lower half of the SATA LBA space to the lower actuator and the
upper half to the upper actuator.
Evidently, to fully utilize actuators, no actuator must be left idle
or underutilized while there is pending I/O for it. The block layer
must somehow control the load of each actuator individually. This
commit lays the ground for allowing BFQ to provide such a per-actuator
control.
BFQ associates an I/O-request sync bfq_queue with each process doing
synchronous I/O, or with a group of processes, in case of queue
merging. Then BFQ serves one bfq_queue at a time. While in service, a
bfq_queue is emptied in request-position order. Yet the same process,
or group of processes, may generate I/O for different actuators. In
this case, different streams of I/O (each for a different actuator)
get all inserted into the same sync bfq_queue. So there is basically
no individual control on when each stream is served, i.e., on when the
I/O requests of the stream are picked from the bfq_queue and
dispatched to the drive.
This commit enables BFQ to control the service of each actuator
individually for synchronous I/O, by simply splitting each sync
bfq_queue into N queues, one for each actuator. In other words, a sync
bfq_queue is now associated to a pair (process, actuator). As a
consequence of this split, the per-queue proportional-share policy
implemented by BFQ will guarantee that the sync I/O generated for each
actuator, by each process, receives its fair share of service.
This is just a preparatory patch. If the I/O of the same process
happens to be sent to different queues, then each of these queues may
undergo queue merging. To handle this event, the bfq_io_cq data
structure must be properly extended. In addition, stable merging must
be disabled to avoid loss of control on individual actuators. Finally,
also async queues must be split. These issues are described in detail
and addressed in next commits. As for this commit, although multiple
per-process bfq_queues are provided, the I/O of each process or group
of processes is still sent to only one queue, regardless of the
actuator the I/O is for. The forwarding to distinct bfq_queues will be
enabled after addressing the above issues.
[1] https://www.linaro.org/blog/budget-fair-queueing-bfq-linux-io-scheduler-optimizations-for-multi-actuator-sata-hard-drives/
Reviewed-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
Signed-off-by: Gabriele Felici <felicigb@gmail.com>
Signed-off-by: Carmine Zaccagnino <carmine@carminezacc.com>
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Link: https://lore.kernel.org/r/20230103145503.71712-2-paolo.valente@linaro.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
The updating of 'bfqg->ref' should be protected by 'bfqd->lock', however,
during code review, we found that bfq_pd_free() update 'bfqg->ref'
without holding the lock, which is problematic:
1) bfq_pd_free() triggered by removing cgroup is called asynchronously;
2) bfqq will grab bfqg reference, and exit bfqq will drop the reference,
which can concurrent with 1).
Unfortunately, 'bfqd->lock' can't be held here because 'bfqd' might already
be freed in bfq_pd_free(). Fix the problem by using atomic refcount apis.
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20230103084755.1256479-1-yukuai1@huaweicloud.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
The 'bfqd->num_groups_with_pending_reqs' is used when
CONFIG_BFQ_GROUP_IOSCHED is enabled, so let the variables and processes
take effect when CONFIG_BFQ_GROUP_IOSCHED is enabled.
Cc: Yu Kuai <yukuai3@huawei.com>
Signed-off-by: Yuwei Guan <Yuwei.Guan@zeekrlife.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Yu Kuai <yukuai3@huawei.com>
Link: https://lore.kernel.org/r/20221110112622.389332-1-Yuwei.Guan@zeekrlife.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Prevent unnecessary format conversion for bfqg->bfqd in multiple
places.
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Acked-by: Paolo Valente <paolo.valente@unimore.it>
Link: https://lore.kernel.org/r/20221102022542.3621219-6-yukuai1@huaweicloud.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
It's the same with bfq_weights_tree_remove() now.
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Acked-by: Paolo Valente <paolo.valente@linaro.org>
Link: https://lore.kernel.org/r/20220916071942.214222-7-yukuai1@huaweicloud.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
The 'bfq_data' and 'rb_root_cached' can both be accessed through
'bfq_queue', thus only pass 'bfq_queue' as parameter.
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Acked-by: Paolo Valente <paolo.valente@linaro.org>
Link: https://lore.kernel.org/r/20220916071942.214222-6-yukuai1@huaweicloud.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Currently, bfq can't handle sync io concurrently as long as they
are not issued from root group. This is because
'bfqd->num_groups_with_pending_reqs > 0' is always true in
bfq_asymmetric_scenario().
The way that bfqg is counted into 'num_groups_with_pending_reqs':
Before this patch:
1) root group will never be counted.
2) Count if bfqg or it's child bfqgs have pending requests.
3) Don't count if bfqg and it's child bfqgs complete all the requests.
After this patch:
1) root group is counted.
2) Count if bfqg have pending requests.
3) Don't count if bfqg complete all the requests.
With this change, the occasion that only one group is activated can be
detected, and next patch will support concurrent sync io in the
occasion.
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Acked-by: Paolo Valente <paolo.valente@linaro.org>
Link: https://lore.kernel.org/r/20220916071942.214222-4-yukuai1@huaweicloud.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Prepare to refactor the counting of 'num_groups_with_pending_reqs'.
Add a counter in bfq_group, update it while tracking if bfqq have pending
requests and when bfq_bfqq_move() is called.
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Acked-by: Paolo Valente <paolo.valente@linaro.org>
Link: https://lore.kernel.org/r/20220916071942.214222-3-yukuai1@huaweicloud.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
If entity belongs to bfqq, then entity->in_groups_with_pending_reqs
is not used currently. This patch use it to track if bfqq has pending
requests through callers of weights_tree insertion and removal.
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Acked-by: Paolo Valente <paolo.valente@linaro.org>
Link: https://lore.kernel.org/r/20220916071942.214222-2-yukuai1@huaweicloud.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
'bfqd' can be accessed through 'bfqq->bfqd', there is no need to pass
it as a parameter separately.
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20220816015631.1323948-4-yukuai1@huaweicloud.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
While doing code coverage testing(CONFIG_BFQ_CGROUP_DEBUG is disabled), we
found that some functions doesn't have caller, thus remove them.
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20220816015631.1323948-2-yukuai1@huaweicloud.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Use the new blk_opf_t type for arguments and variables that represent
request flags or a bitwise combination of a request operation and
request flags. Rename those variables from 'op' into 'opf'.
This patch does not change any functionality.
Cc: Jan Kara <jack@suse.cz>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Link: https://lore.kernel.org/r/20220714180729.1065367-8-bvanassche@acm.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Currently we look for waker only if current queue has no requests. This
makes sense for bfq queues with a single process however for shared
queues when there is a larger number of processes the condition that
queue has no requests is difficult to meet because often at least one
process has some request in flight although all the others are waiting
for the waker to do the work and this harms throughput. Relax the "no
queued request for bfq queue" condition to "the current task has no
queued requests yet". For this, we also need to start tracking number of
requests in flight for each task.
This patch (together with the following one) restores the performance
for dbench with 128 clients that regressed with commit c65e6fd460
("bfq: Do not let waker requests skip proper accounting") because
this commit makes requests of wakers properly enter BFQ queues and thus
these queues become ineligible for the old waker detection logic.
Dbench results:
Vanilla 5.18-rc3 5.18-rc3 + revert 5.18-rc3 patched
Mean 1237.36 ( 0.00%) 950.16 * 23.21%* 988.35 * 20.12%*
Numbers are time to complete workload so lower is better.
Fixes: c65e6fd460 ("bfq: Do not let waker requests skip proper accounting")
Signed-off-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20220519105235.31397-1-jack@suse.cz
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Pass the cgroup_subsys_state instead of a the blkg so that blktrace
doesn't need to poke into blk-cgroup internals, and give the name a
blk prefix as the current name is way too generic for a public
interface.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Tejun Heo <tj@kernel.org>
Link: https://lore.kernel.org/r/20220420042723.1010598-9-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>
BFQ usage of __bio_blkcg() is a relict from the past. Furthermore if bio
would not be associated with any blkcg, the usage of __bio_blkcg() in
BFQ is prone to races with the task being migrated between cgroups as
__bio_blkcg() calls at different places could return different blkcgs.
Convert BFQ to the new situation where bio->bi_blkg is initialized in
bio_set_dev() and thus practically always valid. This allows us to save
blkcg_gq lookup and noticeably simplify the code.
CC: stable@vger.kernel.org
Fixes: 0fe061b9f0 ("blkcg: fix ref count issue with bio_blkcg() using task_css")
Tested-by: "yukuai (C)" <yukuai3@huawei.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20220401102752.8599-8-jack@suse.cz
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Track whether bfq_group is still online. We cannot rely on
blkcg_gq->online because that gets cleared only after all policies are
offlined and we need something that gets updated already under
bfqd->lock when we are cleaning up our bfq_group to be able to guarantee
that when we see online bfq_group, it will stay online while we are
holding bfqd->lock lock.
CC: stable@vger.kernel.org
Tested-by: "yukuai (C)" <yukuai3@huawei.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20220401102752.8599-7-jack@suse.cz
Signed-off-by: Jens Axboe <axboe@kernel.dk>
When bfqq is shared by multiple processes it can happen that one of the
processes gets moved to a different cgroup (or just starts submitting IO
for different cgroup). In case that happens we need to split the merged
bfqq as otherwise we will have IO for multiple cgroups in one bfqq and
we will just account IO time to wrong entities etc.
Similarly if the bfqq is scheduled to merge with another bfqq but the
merge didn't happen yet, cancel the merge as it need not be valid
anymore.
CC: stable@vger.kernel.org
Fixes: e21b7a0b98 ("block, bfq: add full hierarchical scheduling and cgroups support")
Tested-by: "yukuai (C)" <yukuai3@huawei.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20220401102752.8599-3-jack@suse.cz
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Use bfq_group() instead, which do the same thing.
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Acked-by: Paolo Valente <paolo.valente@linaro.org>
Link: https://lore.kernel.org/r/20220129015924.3958918-2-yukuai3@huawei.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Partition include/linux/blk-cgroup.h into two parts: one is public part,
the other is block layer private part.
Suggested by Christoph Hellwig.
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20220211101149.2368042-4-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Instead of having helper formating bfqq pid, provide a helper to
generate full bfqq name as used in the traces. It saves some code
duplication and will save more in the coming tracepoints.
Acked-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20211125133645.27483-6-jack@suse.cz
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Currently, when process A starts issuing requests shortly after process
B has completed some IO three times in a row, we decide that B is a
"waker" of A meaning that completing IO of B is needed for A to make
progress and generally stop separating A's and B's IO much. This logic
is useful to avoid unnecessary idling and thus throughput loss for cases
where workload needs to switch e.g. between the process and the
journaling thread doing IO. However the detection heuristic tends to
frequently give false positives when A and B are fighting IO bandwidth
and other processes aren't doing much IO as we are basically deemed to
eventually accumulate three occurences of a situation where one process
starts issuing requests after the other has completed some IO. To reduce
these false positives, cancel the waker detection also if we didn't
accumulate three detected wakeups within given timeout. The rationale is
that if wakeups are really rare, the pointless idling doesn't hurt
throughput that much anyway.
This significantly reduces false waker detection for workload like:
[global]
directory=/mnt/repro/
rw=write
size=8g
time_based
runtime=30
ramp_time=10
blocksize=1m
direct=0
ioengine=sync
[slowwriter]
numjobs=1
fsync=200
[fastwriter]
numjobs=1
fsync=200
Acked-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20211125133645.27483-5-jack@suse.cz
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Store bitmap depth shift inside bfq_data so that we can use it in
bfq_limit_depth() for proportioning when limiting number of available
request tags for a cgroup.
Acked-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20211125133645.27483-3-jack@suse.cz
Signed-off-by: Jens Axboe <axboe@kernel.dk>
When we want to limit number of requests used by each bfqq and also
cgroup, we need to track also number of requests used by each cgroup.
So track number of allocated requests for each bfq_entity.
Acked-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20211125133645.27483-2-jack@suse.cz
Signed-off-by: Jens Axboe <axboe@kernel.dk>
The BFQ scheduler and ioprio_check_cap() both assume that the RT
priority class (IOPRIO_CLASS_RT) can have up to 8 different priority
levels, similarly to the BE class (IOPRIO_CLASS_iBE). This is
controlled using the IOPRIO_BE_NR macro , which is badly named as the
number of levels also applies to the RT class.
Introduce the class independent IOPRIO_NR_LEVELS macro, defined to 8,
to make things clear. Keep the old IOPRIO_BE_NR macro definition as an
alias for IOPRIO_NR_LEVELS.
Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
Link: https://lore.kernel.org/r/20210811033702.368488-6-damien.lemoal@wdc.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Many throughput-sensitive workloads are made of several parallel I/O
flows, with all flows generated by the same application, or more
generically by the same task (e.g., system boot). The most
counterproductive action with these workloads is plugging I/O dispatch
when one of the bfq_queues associated with these flows remains
temporarily empty.
To avoid this plugging, BFQ has been using a burst-handling mechanism
for years now. This mechanism has proven effective for throughput, and
not detrimental for service guarantees. This commit pushes this
mechanism a little bit further, basing on the following two facts.
First, all the I/O flows of a the same application or task contribute
to the execution/completion of that common application or task. So the
performance figures that matter are total throughput of the flows and
task-wide I/O latency. In particular, these flows do not need to be
protected from each other, in terms of individual bandwidth or
latency.
Second, the above fact holds regardless of the number of flows.
Putting these two facts together, this commits merges stably the
bfq_queues associated with these I/O flows, i.e., with the processes
that generate these IO/ flows, regardless of how many the involved
processes are.
To decide whether a set of bfq_queues is actually associated with the
I/O flows of a common application or task, and to merge these queues
stably, this commit operates as follows: given a bfq_queue, say Q2,
currently being created, and the last bfq_queue, say Q1, created
before Q2, Q2 is merged stably with Q1 if
- very little time has elapsed since when Q1 was created
- Q2 has the same ioprio as Q1
- Q2 belongs to the same group as Q1
Merging bfq_queues also reduces scheduling overhead. A fio test with
ten random readers on /dev/nullb shows a throughput boost of 40%, with
a quadcore. Since BFQ's execution time amounts to ~50% of the total
per-request processing time, the above throughput boost implies that
BFQ's overhead is reduced by more than 50%.
Tested-by: Jan Kara <jack@suse.cz>
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Tested-by: Oleksandr Natalenko <oleksandr@natalenko.name>
Link: https://lore.kernel.org/r/20210304174627.161-7-paolo.valente@linaro.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
In the presence of many parallel I/O flows, the detection of waker
bfq_queues suffers from false positives. This commits addresses this
issue by making the filtering of actual wakers more selective. In more
detail, a candidate waker must be found to meet waker requirements
three times before being promoted to actual waker.
Tested-by: Jan Kara <jack@suse.cz>
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
To prevent injection information from being lost on bfq_queue merging,
also the amount of service that a bfq_queue receives must be saved and
restored when the bfq_queue is merged and split, respectively.
Tested-by: Jan Kara <jack@suse.cz>
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
To prevent weight-raising information from being lost on bfq_queue merging,
also the amount of service that a bfq_queue receives must be saved and
restored when the bfq_queue is merged and split, respectively.
Tested-by: Jan Kara <jack@suse.cz>
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Some BFQ mechanisms make their decisions on a bfq_queue basing also on
whether the bfq_queue is I/O bound. In this respect, the current logic
for evaluating whether a bfq_queue is I/O bound is rather rough. This
commits replaces this logic with a more effective one.
The new logic measures the percentage of time during which a bfq_queue
is active, and marks the bfq_queue as I/O bound if the latter if this
percentage is above a fixed threshold.
Tested-by: Jan Kara <jack@suse.cz>
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Changes from v1:
- update commit description with proper ref-accounting justification
commit db37a34c56 ("block, bfq: get a ref to a group when adding it to a service tree")
introduce leak forbfq_group and blkcg_gq objects because of get/put
imbalance.
In fact whole idea of original commit is wrong because bfq_group entity
can not dissapear under us because it is referenced by child bfq_queue's
entities from here:
-> bfq_init_entity()
->bfqg_and_blkg_get(bfqg);
->entity->parent = bfqg->my_entity
-> bfq_put_queue(bfqq)
FINAL_PUT
->bfqg_and_blkg_put(bfqq_group(bfqq))
->kmem_cache_free(bfq_pool, bfqq);
So parent entity can not disappear while child entity is in tree,
and child entities already has proper protection.
This patch revert commit db37a34c56 ("block, bfq: get a ref to a group when adding it to a service tree")
bfq_group leak trace caused by bad commit:
-> blkg_alloc
-> bfq_pq_alloc
-> bfqg_get (+1)
->bfq_activate_bfqq
->bfq_activate_requeue_entity
-> __bfq_activate_entity
->bfq_get_entity
->bfqg_and_blkg_get (+1) <==== : Note1
->bfq_del_bfqq_busy
->bfq_deactivate_entity+0x53/0xc0 [bfq]
->__bfq_deactivate_entity+0x1b8/0x210 [bfq]
-> bfq_forget_entity(is_in_service = true)
entity->on_st_or_in_serv = false <=== :Note2
if (is_in_service)
return; ==> do not touch reference
-> blkcg_css_offline
-> blkcg_destroy_blkgs
-> blkg_destroy
-> bfq_pd_offline
-> __bfq_deactivate_entity
if (!entity->on_st_or_in_serv) /* true, because (Note2)
return false;
-> bfq_pd_free
-> bfqg_put() (-1, byt bfqg->ref == 2) because of (Note2)
So bfq_group and blkcg_gq will leak forever, see test-case below.
##TESTCASE_BEGIN:
#!/bin/bash
max_iters=${1:-100}
#prep cgroup mounts
mount -t tmpfs cgroup_root /sys/fs/cgroup
mkdir /sys/fs/cgroup/blkio
mount -t cgroup -o blkio none /sys/fs/cgroup/blkio
# Prepare blkdev
grep blkio /proc/cgroups
truncate -s 1M img
losetup /dev/loop0 img
echo bfq > /sys/block/loop0/queue/scheduler
grep blkio /proc/cgroups
for ((i=0;i<max_iters;i++))
do
mkdir -p /sys/fs/cgroup/blkio/a
echo 0 > /sys/fs/cgroup/blkio/a/cgroup.procs
dd if=/dev/loop0 bs=4k count=1 of=/dev/null iflag=direct 2> /dev/null
echo 0 > /sys/fs/cgroup/blkio/cgroup.procs
rmdir /sys/fs/cgroup/blkio/a
grep blkio /proc/cgroups
done
##TESTCASE_END:
Fixes: db37a34c56 ("block, bfq: get a ref to a group when adding it to a service tree")
Tested-by: Oleksandr Natalenko <oleksandr@natalenko.name>
Signed-off-by: Dmitry Monakhov <dmtrmonakhov@yandex-team.ru>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
A bfq_put_queue() may be invoked in __bfq_bic_change_cgroup(). The
goal of this put is to release a process reference to a bfq_queue. But
process-reference releases may trigger also some extra operation, and,
to this goal, are handled through bfq_release_process_ref(). So, turn
the invocation of bfq_put_queue() into an invocation of
bfq_release_process_ref().
Tested-by: cki-project@redhat.com
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
BFQ schedules generic entities, which may represent either bfq_queues
or groups of bfq_queues. When an entity is inserted into a service
tree, a reference must be taken, to make sure that the entity does not
disappear while still referred in the tree. Unfortunately, such a
reference is mistakenly taken only if the entity represents a
bfq_queue. This commit takes a reference also in case the entity
represents a group.
Tested-by: Oleksandr Natalenko <oleksandr@natalenko.name>
Tested-by: Chris Evich <cevich@redhat.com>
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
The flag on_st in the bfq_entity data structure is true if the entity
is on a service tree or is in service. Yet the name of the field,
confusingly, does not mention the second, very important case. Extend
the name to mention the second case too.
Tested-by: Oleksandr Natalenko <oleksandr@natalenko.name>
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
blkg_rwstat is now only used by bfq-iosched and blk-throtl when on
cgroup1. Let's move it into its own files and gate it behind a config
option.
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
When used on cgroup1, bfq uses the blkg->stat_bytes and ->stat_ios
from blk-cgroup core to populate six stat knobs. blk-cgroup core is
moving away from blkg_rwstat to improve scalability and won't be able
to support this usage.
It isn't like the sharing gains all that much. Let's break it out to
dedicated rwstat counters which are updated when on cgroup1. This
makes use of bfqg_*rwstat*() helpers outside of
CONFIG_BFQ_CGROUP_DEBUG. Move them out.
v2: Compile fix when !CONFIG_BFQ_CGROUP_DEBUG.
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
A bfq_queue Q may happen to be synchronized with another
bfq_queue Q2, i.e., the I/O of Q2 may need to be completed for Q to
receive new I/O. We call Q2 "waker queue".
If I/O plugging is being performed for Q, and Q is not receiving any
more I/O because of the above synchronization, then, thanks to BFQ's
injection mechanism, the waker queue is likely to get served before
the I/O-plugging timeout fires.
Unfortunately, this fact may not be sufficient to guarantee a high
throughput during the I/O plugging, because the inject limit for Q may
be too low to guarantee a lot of injected I/O. In addition, the
duration of the plugging, i.e., the time before Q finally receives new
I/O, may not be minimized, because the waker queue may happen to be
served only after other queues.
To address these issues, this commit introduces the explicit detection
of the waker queue, and the unconditional injection of a pending I/O
request of the waker queue on each invocation of
bfq_dispatch_request().
One may be concerned that this systematic injection of I/O from the
waker queue delays the service of Q's I/O. Fortunately, it doesn't. On
the contrary, next Q's I/O is brought forward dramatically, for it is
not blocked for milliseconds.
Reported-by: Srivatsa S. Bhat (VMware) <srivatsa@csail.mit.edu>
Tested-by: Srivatsa S. Bhat (VMware) <srivatsa@csail.mit.edu>
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This option is entirely bfq specific, give it an appropinquate name.
Also make it depend on CONFIG_BFQ_GROUP_IOSCHED in Kconfig, as all
the functionality already does so anyway.
Acked-by: Tejun Heo <tj@kernel.org>
Acked-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This structure and assorted infrastructure is only used by the bfq I/O
scheduler. Move it there instead of bloating the common code.
Acked-by: Tejun Heo <tj@kernel.org>
Acked-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
All these files have some form of the usual GPLv2 or later boilerplate.
Switch them to use SPDX tags instead.
Reviewed-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
