Commit Graph

86 Commits

Author SHA1 Message Date
Tejun Heo bd0adb91a6 blk-iocost: use WEIGHT_ONE based fixed point number for weights
To improve weight donations, we want to able to scale inuse with a greater
accuracy and down below 1. Let's make non-hierarchical weights to use
WEIGHT_ONE based fixed point numbers too like hierarchical ones.

This doesn't cause any behavior changes yet.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2020-09-01 19:38:32 -06:00
Tejun Heo fe20cdb516 blk-iocost: s/HWEIGHT_WHOLE/WEIGHT_ONE/g
We're gonna use HWEIGHT_WHOLE for regular weights too. Let's rename it to
WEIGHT_ONE.

Pure rename.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2020-09-01 19:38:32 -06:00
Tejun Heo 7b84b49e38 blk-iocost: make iocg_kick_waitq() call iocg_kick_delay() after paying debt
iocg_kick_waitq() is the function which pays debt and iocg_kick_delay()
updates the actual delay status accordingly. If iocg_kick_delay() is not
called after iocg_kick_delay() updated debt, unnecessarily large delays can
be applied temporarily.

Let's make sure such conditions don't occur by making iocg_kick_waitq()
always call iocg_kick_delay() after paying debt.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2020-09-01 19:38:31 -06:00
Tejun Heo 6ef20f787b blk-iocost: move iocg_kick_delay() above iocg_kick_waitq()
We'll make iocg_kick_waitq() call iocg_kick_delay(). Reorder them in
preparation. This is pure code reorganization.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2020-09-01 19:38:31 -06:00
Tejun Heo db84a72af6 blk-iocost: clamp inuse and skip noops in __propagate_weights()
__propagate_weights() currently expects the callers to clamp inuse within
[1, active], which is needlessly fragile. The inuse adjustment logic is
going to be revamped, in preparation, let's make __propagate_weights() clamp
inuse on entry.

Also, make it avoid weight updates altogether if neither active or inuse is
changed.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2020-09-01 19:38:31 -06:00
Tejun Heo 00410f1b09 blk-iocost: rename propagate_active_weights() to propagate_weights()
It already propagates two weights - active and inuse - and there will be
another soon. Let's drop the confusing misnomers. Rename
[__]propagate_active_weights() to [__]propagate_weights() and
commit_active_weights() to commit_weights().

This is pure rename.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2020-09-01 19:38:31 -06:00
Tejun Heo 5e124f7432 blk-iocost: use local[64]_t for percpu stat
blk-iocost has been reading percpu stat counters from remote cpus which on
some archs can lead to torn reads in really rare occassions. Use local[64]_t
for those counters.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2020-09-01 19:38:31 -06:00
Tejun Heo 5aeac7c4b1 blk-iocost: ioc_pd_free() shouldn't assume irq disabled
ioc_pd_free() grabs irq-safe ioc->lock without ensuring that irq is disabled
when it can be called with irq disabled or enabled. This has a small chance
of causing A-A deadlocks and triggers lockdep splats. Use irqsave operations
instead.

Signed-off-by: Tejun Heo <tj@kernel.org>
Fixes: 7caa47151a ("blkcg: implement blk-iocost")
Cc: stable@vger.kernel.org # v5.4+
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2020-09-01 16:48:44 -06:00
Linus Torvalds 97d052ea3f A set of locking fixes and updates:
- Untangle the header spaghetti which causes build failures in various
     situations caused by the lockdep additions to seqcount to validate that
     the write side critical sections are non-preemptible.
 
   - The seqcount associated lock debug addons which were blocked by the
     above fallout.
 
     seqcount writers contrary to seqlock writers must be externally
     serialized, which usually happens via locking - except for strict per
     CPU seqcounts. As the lock is not part of the seqcount, lockdep cannot
     validate that the lock is held.
 
     This new debug mechanism adds the concept of associated locks.
     sequence count has now lock type variants and corresponding
     initializers which take a pointer to the associated lock used for
     writer serialization. If lockdep is enabled the pointer is stored and
     write_seqcount_begin() has a lockdep assertion to validate that the
     lock is held.
 
     Aside of the type and the initializer no other code changes are
     required at the seqcount usage sites. The rest of the seqcount API is
     unchanged and determines the type at compile time with the help of
     _Generic which is possible now that the minimal GCC version has been
     moved up.
 
     Adding this lockdep coverage unearthed a handful of seqcount bugs which
     have been addressed already independent of this.
 
     While generaly useful this comes with a Trojan Horse twist: On RT
     kernels the write side critical section can become preemtible if the
     writers are serialized by an associated lock, which leads to the well
     known reader preempts writer livelock. RT prevents this by storing the
     associated lock pointer independent of lockdep in the seqcount and
     changing the reader side to block on the lock when a reader detects
     that a writer is in the write side critical section.
 
  - Conversion of seqcount usage sites to associated types and initializers.
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Merge tag 'locking-urgent-2020-08-10' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull locking updates from Thomas Gleixner:
 "A set of locking fixes and updates:

   - Untangle the header spaghetti which causes build failures in
     various situations caused by the lockdep additions to seqcount to
     validate that the write side critical sections are non-preemptible.

   - The seqcount associated lock debug addons which were blocked by the
     above fallout.

     seqcount writers contrary to seqlock writers must be externally
     serialized, which usually happens via locking - except for strict
     per CPU seqcounts. As the lock is not part of the seqcount, lockdep
     cannot validate that the lock is held.

     This new debug mechanism adds the concept of associated locks.
     sequence count has now lock type variants and corresponding
     initializers which take a pointer to the associated lock used for
     writer serialization. If lockdep is enabled the pointer is stored
     and write_seqcount_begin() has a lockdep assertion to validate that
     the lock is held.

     Aside of the type and the initializer no other code changes are
     required at the seqcount usage sites. The rest of the seqcount API
     is unchanged and determines the type at compile time with the help
     of _Generic which is possible now that the minimal GCC version has
     been moved up.

     Adding this lockdep coverage unearthed a handful of seqcount bugs
     which have been addressed already independent of this.

     While generally useful this comes with a Trojan Horse twist: On RT
     kernels the write side critical section can become preemtible if
     the writers are serialized by an associated lock, which leads to
     the well known reader preempts writer livelock. RT prevents this by
     storing the associated lock pointer independent of lockdep in the
     seqcount and changing the reader side to block on the lock when a
     reader detects that a writer is in the write side critical section.

   - Conversion of seqcount usage sites to associated types and
     initializers"

* tag 'locking-urgent-2020-08-10' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (25 commits)
  locking/seqlock, headers: Untangle the spaghetti monster
  locking, arch/ia64: Reduce <asm/smp.h> header dependencies by moving XTP bits into the new <asm/xtp.h> header
  x86/headers: Remove APIC headers from <asm/smp.h>
  seqcount: More consistent seqprop names
  seqcount: Compress SEQCNT_LOCKNAME_ZERO()
  seqlock: Fold seqcount_LOCKNAME_init() definition
  seqlock: Fold seqcount_LOCKNAME_t definition
  seqlock: s/__SEQ_LOCKDEP/__SEQ_LOCK/g
  hrtimer: Use sequence counter with associated raw spinlock
  kvm/eventfd: Use sequence counter with associated spinlock
  userfaultfd: Use sequence counter with associated spinlock
  NFSv4: Use sequence counter with associated spinlock
  iocost: Use sequence counter with associated spinlock
  raid5: Use sequence counter with associated spinlock
  vfs: Use sequence counter with associated spinlock
  timekeeping: Use sequence counter with associated raw spinlock
  xfrm: policy: Use sequence counters with associated lock
  netfilter: nft_set_rbtree: Use sequence counter with associated rwlock
  netfilter: conntrack: Use sequence counter with associated spinlock
  sched: tasks: Use sequence counter with associated spinlock
  ...
2020-08-10 19:07:44 -07:00
Chengming Zhou d9012a59db iocost: Fix check condition of iocg abs_vdebt
We shouldn't skip iocg when its abs_vdebt is not zero.

Fixes: 0b80f9866e ("iocost: protect iocg->abs_vdebt with iocg->waitq.lock")
Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2020-07-30 11:45:12 -06:00
Ahmed S. Darwish 67b7b641ca iocost: Use sequence counter with associated spinlock
A sequence counter write side critical section must be protected by some
form of locking to serialize writers. A plain seqcount_t does not
contain the information of which lock must be held when entering a write
side critical section.

Use the new seqcount_spinlock_t data type, which allows to associate a
spinlock with the sequence counter. This enables lockdep to verify that
the spinlock used for writer serialization is held when the write side
critical section is entered.

If lockdep is disabled this lock association is compiled out and has
neither storage size nor runtime overhead.

Signed-off-by: Ahmed S. Darwish <a.darwish@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Daniel Wagner <dwagner@suse.de>
Link: https://lkml.kernel.org/r/20200720155530.1173732-21-a.darwish@linutronix.de
2020-07-29 16:14:28 +02:00
Gustavo A. R. Silva f61d6e259c blk-iocost: Use struct_size() in kzalloc_node()
Make use of the struct_size() helper instead of an open-coded version
in order to avoid any potential type mistakes.

This code was detected with the help of Coccinelle and, audited and
fixed manually.

Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Addresses-KSPP-ID: https://github.com/KSPP/linux/issues/83
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2020-06-24 09:15:58 -06:00
Tejun Heo 81ca627a93 iocost: don't let vrate run wild while there's no saturation signal
When the QoS targets are met and nothing is being throttled, there's
no way to tell how saturated the underlying device is - it could be
almost entirely idle, at the cusp of saturation or anywhere inbetween.
Given that there's no information, it's best to keep vrate as-is in
this state.  Before 7cd806a9a9 ("iocost: improve nr_lagging
handling"), this was the case - if the device isn't missing QoS
targets and nothing is being throttled, busy_level was reset to zero.

While fixing nr_lagging handling, 7cd806a9a9 ("iocost: improve
nr_lagging handling") broke this.  Now, while the device is hitting
QoS targets and nothing is being throttled, vrate keeps getting
adjusted according to the existing busy_level.

This led to vrate keeping climing till it hits max when there's an IO
issuer with limited request concurrency if the vrate started low.
vrate starts getting adjusted upwards until the issuer can issue IOs
w/o being throttled.  From then on, QoS targets keeps getting met and
nothing on the system needs throttling and vrate keeps getting
increased due to the existing busy_level.

This patch makes the following changes to the busy_level logic.

* Reset busy_level if nr_shortages is zero to avoid the above
  scenario.

* Make non-zero nr_lagging block lowering nr_level but still clear
  positive busy_level if there's clear non-saturation signal - QoS
  targets are met and nr_shortages is non-zero.  nr_lagging's role is
  preventing adjusting vrate upwards while there are long-running
  commands and it shouldn't keep busy_level positive while there's
  clear non-saturation signal.

* Restructure code for clarity and add comments.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Andy Newell <newella@fb.com>
Fixes: 7cd806a9a9 ("iocost: improve nr_lagging handling")
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2020-05-14 09:32:09 -06:00
Jens Axboe 873f1c8df7 Merge branch 'block-5.7' into for-5.8/block
Pull in block-5.7 fixes for 5.8. Mostly to resolve a conflict with
the blk-iocost changes, but we also need the base of the bdi
use-after-free as well as we build on top of it.

* block-5.7:
  nvme: fix possible hang when ns scanning fails during error recovery
  nvme-pci: fix "slimmer CQ head update"
  bdi: add a ->dev_name field to struct backing_dev_info
  bdi: use bdi_dev_name() to get device name
  bdi: move bdi_dev_name out of line
  vboxsf: don't use the source name in the bdi name
  iocost: protect iocg->abs_vdebt with iocg->waitq.lock
  block: remove the bd_openers checks in blk_drop_partitions
  nvme: prevent double free in nvme_alloc_ns() error handling
  null_blk: Cleanup zoned device initialization
  null_blk: Fix zoned command handling
  block: remove unused header
  blk-iocost: Fix error on iocost_ioc_vrate_adj
  bdev: Reduce time holding bd_mutex in sync in blkdev_close()
  buffer: remove useless comment and WB_REASON_FREE_MORE_MEM, reason.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
2020-05-09 16:13:58 -06:00
Tejun Heo 0b80f9866e iocost: protect iocg->abs_vdebt with iocg->waitq.lock
abs_vdebt is an atomic_64 which tracks how much over budget a given cgroup
is and controls the activation of use_delay mechanism. Once a cgroup goes
over budget from forced IOs, it has to pay it back with its future budget.
The progress guarantee on debt paying comes from the iocg being active -
active iocgs are processed by the periodic timer, which ensures that as time
passes the debts dissipate and the iocg returns to normal operation.

However, both iocg activation and vdebt handling are asynchronous and a
sequence like the following may happen.

1. The iocg is in the process of being deactivated by the periodic timer.

2. A bio enters ioc_rqos_throttle(), calls iocg_activate() which returns
   without anything because it still sees that the iocg is already active.

3. The iocg is deactivated.

4. The bio from #2 is over budget but needs to be forced. It increases
   abs_vdebt and goes over the threshold and enables use_delay.

5. IO control is enabled for the iocg's subtree and now IOs are attributed
   to the descendant cgroups and the iocg itself no longer issues IOs.

This leaves the iocg with stuck abs_vdebt - it has debt but inactive and no
further IOs which can activate it. This can end up unduly punishing all the
descendants cgroups.

The usual throttling path has the same issue - the iocg must be active while
throttled to ensure that future event will wake it up - and solves the
problem by synchronizing the throttling path with a spinlock. abs_vdebt
handling is another form of overage handling and shares a lot of
characteristics including the fact that it isn't in the hottest path.

This patch fixes the above and other possible races by strictly
synchronizing abs_vdebt and use_delay handling with iocg->waitq.lock.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Vlad Dmitriev <vvd@fb.com>
Cc: stable@vger.kernel.org # v5.4+
Fixes: e1518f63f2 ("blk-iocost: Don't let merges push vtime into the future")
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2020-05-05 09:23:18 -06:00
Tejun Heo cd006509b0 blk-iocost: account for IO size when testing latencies
On each IO completion, iocost decides whether the IO met or missed its latency
target. Currently, the targets are fixed numbers per IO type. While this can be
good enough for loose latency targets way higher than typical completion
latencies, the effect of IO size makes it difficult to tighten the latency
target - a target adequate for 4k IOs might be too tight for 512k IOs and
vice-versa.

iocost already has all the necessary information to account for different IO
sizes when testing whether the latency target is met as iocost can calculate the
size vtime cost of a given IO. This patch updates the completion path to
calculate the size vtime cost of the IO, deduct the nsec equivalent from the
observed latency and use the adjusted value to decide whether the target is met.

This makes latency targets independent from IO size and enables determining
adequate latency targets with fixed size fio runs.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Andy Newell <newella@fb.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2020-04-30 15:54:45 -06:00
Tejun Heo 54c52e10dc blk-iocost: switch to fixed non-auto-decaying use_delay
The use_delay mechanism was introduced by blk-iolatency to hold memory
allocators accountable for the reclaim and other shared IOs they cause. The
duration of the delay is dynamically balanced between iolatency increasing the
value on each target miss and it auto-decaying as time passes and threads get
delayed on it.

While this works well for iolatency, iocost's control model isn't compatible
with it. There is no repeated "violation" events which can be balanced against
auto-decaying. iocost instead knows how much a given cgroup is over budget and
wants to prevent that cgroup from issuing IOs while over budget. Until now,
iocost has been adding the cost of force-issued IOs. However, this doesn't
reflect the amount which is already over budget and is simply not enough to
counter the auto-decaying allowing anon-memory leaking low priority cgroup to
go over its alloted share of IOs.

As auto-decaying doesn't make much sense for iocost, this patch introduces a
different mode of operation for use_delay - when blkcg_set_delay() are used
insted of blkcg_add/use_delay(), the delay duration is not auto-decayed until it
is explicitly cleared with blkcg_clear_delay(). iocost is updated to keep the
delay duration synchronized to the budget overage amount.

With this change, iocost can effectively police cgroups which generate
significant amount of force-issued IOs.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2020-04-30 15:54:45 -06:00
Waiman Long d6c8e949a3 blk-iocost: Fix error on iocost_ioc_vrate_adj
Systemtap 4.2 is unable to correctly interpret the "u32 (*missed_ppm)[2]"
argument of the iocost_ioc_vrate_adj trace entry defined in
include/trace/events/iocost.h leading to the following error:

  /tmp/stapAcz0G0/stap_c89c58b83cea1724e26395efa9ed4939_6321_aux_6.c:78:8:
  error: expected ‘;’, ‘,’ or ‘)’ before ‘*’ token
   , u32[]* __tracepoint_arg_missed_ppm

That argument type is indeed rather complex and hard to read. Looking
at block/blk-iocost.c. It is just a 2-entry u32 array. By simplifying
the argument to a simple "u32 *missed_ppm" and adjusting the trace
entry accordingly, the compilation error was gone.

Fixes: 7caa47151a ("blkcg: implement blk-iocost")
Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2020-04-21 09:49:36 -06:00
Linus Torvalds 10f36b1e80 for-5.7/block-2020-03-29
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Merge tag 'for-5.7/block-2020-03-29' of git://git.kernel.dk/linux-block

Pull block updates from Jens Axboe:

 - Online capacity resizing (Balbir)

 - Number of hardware queue change fixes (Bart)

 - null_blk fault injection addition (Bart)

 - Cleanup of queue allocation, unifying the node/no-node API
   (Christoph)

 - Cleanup of genhd, moving code to where it makes sense (Christoph)

 - Cleanup of the partition handling code (Christoph)

 - disk stat fixes/improvements (Konstantin)

 - BFQ improvements (Paolo)

 - Various fixes and improvements

* tag 'for-5.7/block-2020-03-29' of git://git.kernel.dk/linux-block: (72 commits)
  block: return NULL in blk_alloc_queue() on error
  block: move bio_map_* to blk-map.c
  Revert "blkdev: check for valid request queue before issuing flush"
  block: simplify queue allocation
  bcache: pass the make_request methods to blk_queue_make_request
  null_blk: use blk_mq_init_queue_data
  block: add a blk_mq_init_queue_data helper
  block: move the ->devnode callback to struct block_device_operations
  block: move the part_stat* helpers from genhd.h to a new header
  block: move block layer internals out of include/linux/genhd.h
  block: move guard_bio_eod to bio.c
  block: unexport get_gendisk
  block: unexport disk_map_sector_rcu
  block: unexport disk_get_part
  block: mark part_in_flight and part_in_flight_rw static
  block: mark block_depr static
  block: factor out requeue handling from dispatch code
  block/diskstats: replace time_in_queue with sum of request times
  block/diskstats: accumulate all per-cpu counters in one pass
  block/diskstats: more accurate approximation of io_ticks for slow disks
  ...
2020-03-30 11:20:13 -07:00
Weiping Zhang fa800d73c8 blk-iocost: remove duplicated lines in comments
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Weiping Zhang <zhangweiping@didiglobal.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2020-03-12 08:02:20 -06:00
Tejun Heo dcd6589b11 blk-iocost: fix incorrect vtime comparison in iocg_is_idle()
vtimes may wrap and time_before/after64() should be used to determine
whether a given vtime is before or after another. iocg_is_idle() was
incorrectly using plain "<" comparison do determine whether done_vtime
is before vtime. Here, the only thing we're interested in is whether
done_vtime matches vtime which indicates that there's nothing in
flight. Let's test for inequality instead.

Signed-off-by: Tejun Heo <tj@kernel.org>
Fixes: 7caa47151a ("blkcg: implement blk-iocost")
Cc: stable@vger.kernel.org # v5.4+
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2020-03-10 11:37:00 -06:00
Tejun Heo d7bd15a138 iocost: over-budget forced IOs should schedule async delay
When over-budget IOs are force-issued through root cgroup,
iocg_kick_delay() adjusts the async delay accordingly but doesn't
actually schedule async throttle for the issuing task.  This bug is
pretty well masked because sooner or later the offending threads are
gonna get directly throttled on regular IOs or have async delay
scheduled by mem_cgroup_throttle_swaprate().

However, it can affect control quality on filesystem metadata heavy
operations.  Let's fix it by invoking blkcg_schedule_throttle() when
iocg_kick_delay() says async delay is needed.

Signed-off-by: Tejun Heo <tj@kernel.org>
Fixes: 7caa47151a ("blkcg: implement blk-iocost")
Cc: stable@vger.kernel.org
Reported-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2019-12-16 16:10:17 -07:00
Jiufei Xue 8b37bc277f iocost: check active_list of all the ancestors in iocg_activate()
There is a bug that checking the same active_list over and over again
in iocg_activate(). The intention of the code was checking whether all
the ancestors and self have already been activated. So fix it.

Fixes: 7caa47151a ("blkcg: implement blk-iocost")
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jiufei Xue <jiufei.xue@linux.alibaba.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2019-11-14 13:56:54 -07:00
Dan Carpenter 41591a51f0 iocost: don't nest spin_lock_irq in ioc_weight_write()
This code causes a static analysis warning:

    block/blk-iocost.c:2113 ioc_weight_write() error: double lock 'irq'

We disable IRQs in blkg_conf_prep() and re-enable them in
blkg_conf_finish().  IRQ disable/enable should not be nested because
that means the IRQs will be enabled at the first unlock instead of the
second one.

Fixes: 7caa47151a ("blkcg: implement blk-iocost")
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2019-10-31 11:40:57 -06:00
Tejun Heo 7afcccafa5 iocost: bump up default latency targets for hard disks
The default hard disk param sets latency targets at 50ms.  As the
default target percentiles are zero, these don't directly regulate
vrate; however, they're still used to calculate the period length -
100ms in this case.

This is excessively low.  A SATA drive with QD32 saturated with random
IOs can easily reach avg completion latency of several hundred msecs.
A period duration which is substantially lower than avg completion
latency can lead to wildly fluctuating vrate.

Let's bump up the default latency targets to 250ms so that the period
duration is sufficiently long.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2019-09-26 01:12:01 -06:00
Tejun Heo 7cd806a9a9 iocost: improve nr_lagging handling
Some IOs may span multiple periods.  As latencies are collected on
completion, the inbetween periods won't register them and may
incorrectly decide to increase vrate.  nr_lagging tracks these IOs to
avoid those situations.  Currently, whenever there are IOs which are
spanning from the previous period, busy_level is reset to 0 if
negative thus suppressing vrate increase.

This has the following two problems.

* When latency target percentiles aren't set, vrate adjustment should
  only be governed by queue depth depletion; however, the current code
  keeps nr_lagging active which pulls in latency results and can keep
  down vrate unexpectedly.

* When lagging condition is detected, it resets the entire negative
  busy_level.  This turned out to be way too aggressive on some
  devices which sometimes experience extended latencies on a small
  subset of commands.  In addition, a lagging IO will be accounted as
  latency target miss on completion anyway and resetting busy_level
  amplifies its impact unnecessarily.

This patch fixes the above two problems by disabling nr_lagging
counting when latency target percentiles aren't set and blocking vrate
increases when there are lagging IOs while leaving busy_level as-is.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2019-09-26 01:12:00 -06:00
Tejun Heo 25d41e4aad iocost: better trace vrate changes
vrate_adj tracepoint traces vrate changes; however, it does so only
when busy_level is non-zero.  busy_level turning to zero can sometimes
be as interesting an event.  This patch also enables vrate_adj
tracepoint on other vrate related events - busy_level changes and
non-zero nr_lagging.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2019-09-26 01:11:58 -06:00
Tejun Heo 7c1ee704a1 iocost_monitor: Report debt
Report debt and rename del_ms row to delay for consistency.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2019-09-10 12:31:39 -06:00
Tejun Heo e1518f63f2 blk-iocost: Don't let merges push vtime into the future
Merges have the same problem that forced-bios had which is fixed by
the previous patch.  The cost of a merge is calculated at the time of
issue and force-advances vtime into the future.  Until global vtime
catches up, how the cgroup's hweight changes in the meantime doesn't
matter and it often leads to situations where the cost is calculated
at one hweight and paid at a very different one.  See the previous
patch for more details.

Fix it by never advancing vtime into the future for merges.  If budget
is available, vtime is advanced.  Otherwise, the cost is charged as
debt.

This brings merge cost handling in line with issue cost handling in
ioc_rqos_throttle().

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2019-09-10 12:31:39 -06:00
Tejun Heo 36a524814f blk-iocost: Account force-charged overage in absolute vtime
Currently, when a bio needs to be force-charged and there isn't enough
budget, vtime is simply pushed into the future.  This means that the
cost of the whole bio is scaled using the current hweight and then
charged immediately.  Until the global vtime advances beyond this
future vtime, the cgroup won't be allowed to issue normal IOs.

This is incorrect and can lead to, for example, exploding vrate or
extended stalls if vrate range is constrained.  Consider the following
scenario.

1. A cgroup with a very low hweight runs out of budget.

2. A storm of swap-out happens on it.  All of them are scaled
   according to the current low hweight and charged to vtime pushing
   it to a far future.

3. All other cgroups go idle and now the above cgroup has access to
   the whole device.  However, because vtime is already wound using
   the past low hweight, what its current hweight is doesn't matter
   until global vtime catches up to the local vtime.

4. As a result, either vrate gets ramped up extremely or the IOs stall
   while the underlying device is idle.

This is because the hweight the overage is calculated at is different
from the hweight that it's being paid at.

Fix it by remembering the overage in absoulte vtime and continuously
paying with the actual budget according to the current hweight at each
period.

Note that non-forced bios which wait already remembers the cost in
absolute vtime.  This brings forced-bio accounting in line.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2019-09-10 12:31:39 -06:00
Tejun Heo e036c4caba blk-iocost: Fix incorrect operation order during iocg free
ioc_pd_free() first cancels the hrtimers and then deactivates the
iocg.  However, the iocg timer can run inbetween and reschedule the
hrtimers which will end up running after the iocg is freed leading to
crashes like the following.

  general protection fault: 0000 [#1] SMP
  ...
  RIP: 0010:iocg_kick_delay+0xbe/0x1b0
  RSP: 0018:ffffc90003598ea0 EFLAGS: 00010046
  RAX: 1cee00fd69512b54 RBX: ffff8881bba48400 RCX: 00000000000003e8
  RDX: 0000000000000000 RSI: 0000000000000001 RDI: ffff8881bba48400
  RBP: 0000000000004e20 R08: 0000000000000002 R09: 00000000000003e8
  R10: 0000000000000000 R11: 0000000000000000 R12: ffffc90003598ef0
  R13: 00979f3810ad461f R14: ffff8881bba4b400 R15: 25439f950d26e1d1
  FS:  0000000000000000(0000) GS:ffff88885f800000(0000) knlGS:0000000000000000
  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
  CR2: 00007f64328c7e40 CR3: 0000000002409005 CR4: 00000000003606e0
  DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
  DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
  Call Trace:
   <IRQ>
   iocg_delay_timer_fn+0x3d/0x60
   __hrtimer_run_queues+0xfe/0x270
   hrtimer_interrupt+0xf4/0x210
   smp_apic_timer_interrupt+0x5e/0x120
   apic_timer_interrupt+0xf/0x20
   </IRQ>

Fix it by canceling hrtimers after deactivating the iocg.

Fixes: 7caa47151a ("blkcg: implement blk-iocost")
Reported-by: Dave Jones <davej@codemonkey.org.uk>
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2019-09-10 12:17:04 -06:00
Tejun Heo e916ad29d9 blkcg: add missing NULL check in ioc_cpd_alloc()
ioc_cpd_alloc() forgot to check NULL return from kzalloc().  Add it.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2019-08-30 07:16:19 -06:00
Tejun Heo 3532e72272 blkcg: fix missing free on error path of blk_iocost_init()
blk_iocost_init() forgot to free its percpu stat on the error path.
Fix it.

Fixes: 7caa47151a ("blkcg: implement blk-iocost")
Reported-by: Hillf Danton <hdanton@sina.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2019-08-29 09:59:14 -06:00
Tejun Heo 8504dea783 blkcg: add tools/cgroup/iocost_coef_gen.py
Add a script which can be used to generate device-specific iocost
linear model coefficients.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2019-08-28 21:17:17 -06:00
Tejun Heo 6954ff185e blkcg: add tools/cgroup/iocost_monitor.py
Instead of mucking with debugfs and ->pd_stat(), add drgn based
monitoring script.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Omar Sandoval <osandov@fb.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2019-08-28 21:17:14 -06:00
Tejun Heo 7caa47151a blkcg: implement blk-iocost
This patchset implements IO cost model based work-conserving
proportional controller.

While io.latency provides the capability to comprehensively prioritize
and protect IOs depending on the cgroups, its protection is binary -
the lowest latency target cgroup which is suffering is protected at
the cost of all others.  In many use cases including stacking multiple
workload containers in a single system, it's necessary to distribute
IO capacity with better granularity.

One challenge of controlling IO resources is the lack of trivially
observable cost metric.  The most common metrics - bandwidth and iops
- can be off by orders of magnitude depending on the device type and
IO pattern.  However, the cost isn't a complete mystery.  Given
several key attributes, we can make fairly reliable predictions on how
expensive a given stream of IOs would be, at least compared to other
IO patterns.

The function which determines the cost of a given IO is the IO cost
model for the device.  This controller distributes IO capacity based
on the costs estimated by such model.  The more accurate the cost
model the better but the controller adapts based on IO completion
latency and as long as the relative costs across differents IO
patterns are consistent and sensible, it'll adapt to the actual
performance of the device.

Currently, the only implemented cost model is a simple linear one with
a few sets of default parameters for different classes of device.
This covers most common devices reasonably well.  All the
infrastructure to tune and add different cost models is already in
place and a later patch will also allow using bpf progs for cost
models.

Please see the top comment in blk-iocost.c and documentation for
more details.

v2: Rebased on top of RQ_ALLOC_TIME changes and folded in Rik's fix
    for a divide-by-zero bug in current_hweight() triggered by zero
    inuse_sum.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Andy Newell <newella@fb.com>
Cc: Josef Bacik <jbacik@fb.com>
Cc: Rik van Riel <riel@surriel.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2019-08-28 21:17:12 -06:00