Skip to content

L
linux
Switch branch/tag
  1. 09 May, 2020 27 commits
  3. 07 May, 2020 2 commits
  5. 05 May, 2020 1 commit
    • Tejun Heo's avatar
      iocost: protect iocg->abs_vdebt with iocg->waitq.lock · 0b80f986
      Tejun Heo authored 
      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: default avatarTejun Heo <tj@kernel.org>
Reported-by: default avatarVlad Dmitriev <vvd@fb.com>
Cc: stable@vger.kernel.org # v5.4+
Fixes: e1518f63 ("blk-iocost: Don't let merges push vtime into the future")
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
      0b80f986
  7. 04 May, 2020 7 commits
  9. 30 Apr, 2020 3 commits
    • Tejun Heo's avatar
      iocost_monitor: drop string wrap around numbers when outputting json · 21f3cfea
      Tejun Heo authored 
      Wrapping numbers in strings is used by some to work around bit-width issues in
some enviroments. The problem isn't innate to json and the workaround seems to
cause more integration problems than help. Let's drop the string wrapping.
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
      21f3cfea
    • Tejun Heo's avatar
      iocost_monitor: exit successfully if interval is zero · f4fe3ea6
      Tejun Heo authored 
      This is to help external tools to decide whether iocost_monitor has all its
requirements met or not based on the exit status of an -i0 run.
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
      f4fe3ea6
    • Tejun Heo's avatar
      blk-iocost: account for IO size when testing latencies · cd006509
      Tejun Heo authored 
      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: default avatarTejun Heo <tj@kernel.org>
Cc: Andy Newell <newella@fb.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
      cd006509
GitLab Nexedi Edition | About GitLab | About Nexedi | 沪ICP备2021021310号-2 | 沪ICP备2021021310号-7