iocost_monitor: improve it by adding iocg wait_ms

The iocg can have three throttled metrics: wait, debt, delay. This patch
add missing wait_ms to IocgStat to show the latest wait_ms of iocg.

As we are here, group iocg usage percents "inflt%" and "usage%" together,
and group iocg throttled metrics "wait", "debt" and "delay" together.

Effect after changes:

nvme0n1 RUN per=50.0ms cur_per=177105.713:v1053528.587 busy= +0 vrate=135.00%:270.00% params=ssd_dfl(CQ)
active weight hweight% inflt% usage% wait debt delay
InterfererGroup0 * 100/ 100 54.28/ 9.09 0.34 24.07 0.00 0.00 0.00
interfered * 84/ 1000 45.72/ 90.91 0.48 41.09 0.00 0.00 0.00

Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>
Acked-by: Tejun Heo <tj@kernel.org>
Link: https://lore.kernel.org/r/20230804065039.8885-3-chengming.zhou@linux.dev
Signed-off-by: Jens Axboe <axboe@kernel.dk>

iocost_monitor: print vrate inuse along with base_vrate

The real vrate iocost inuse is not base_vrate, but the atomic vtime_rate.
We need iocost_monitor tool to display this real vrate that iocost use,
to check if the boosted compensated vrate is normal.

Effect after change:

nvme0n1 RUN per=50.0ms cur_per=172116.580:v1040587.433 busy= +0 \
vrate=135.00%:270.00% params=ssd_dfl(CQ)
^
|
this is real vrate inuse

Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>
Link: https://lore.kernel.org/r/20230804065039.8885-2-chengming.zhou@linux.dev
Signed-off-by: Jens Axboe <axboe@kernel.dk>

iocost_monitor: fix kernel queue kobj changes

When I use iocost_monitor on nvme0n1, this error shows up:
"Could not find ioc for nvme0n1"

There is no kobj in struct queue in recent kernel, it seems that the commit
2bd85221a625 ("block: untangle request_queue refcounting from sysfs")
move the queue kobj to struct gendisk.

Fix it by using mq_kobj which is at the same level with queue kobj.

Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>
Link: https://lore.kernel.org/r/20230804065039.8885-1-chengming.zhou@linux.dev
Signed-off-by: Jens Axboe <axboe@kernel.dk>

iocost_monitor: reorder BlkgIterator

In order to comply with PEP 8, the first parameter of a class should be
__init__.

Signed-off-by: Elijah Conners <business@elijahpepe.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

blk-iocost: update iocost_monitor.py

iocost went through significant internal changes. Update iocost_monitor.py
accordingly.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

iocost_monitor: start from the oldest usage index

iocg usage_idx is the latest usage index, we should start from the
oldest usage index to show the consecutive NR_USAGE_SLOTS usages.

Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

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: e1518f63f246 ("blk-iocost: Don't let merges push vtime into the future")
Signed-off-by: Jens Axboe <axboe@kernel.dk>

iocost_monitor: drop string wrap around numbers when outputting json

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: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

iocost_monitor: exit successfully if interval is zero

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: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

iocost: Fix iocost_monitor.py due to helper type mismatch

iocost_monitor.py broke with recent versions of drgn due to helper
being stricter about types. Fix it so that it uses the correct type.

Signed-off-by: Tejun Heo <tj@kernel.org>
Suggested-by: Omar Sandoval <osandov@fb.com>

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>

iocost_monitor: Report more info with higher accuracy

When outputting json:

* Don't truncate numbers.

* Report address of iocg to ease drilling down further.

When outputting table:

* Use math.ceil() for delay_ms so that small delays don't read as 0.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

iocost_monitor: Always use strings for json values

Json has limited accuracy for numbers and can silently truncate 64bit
values, which can be extremely confusing. Let's consistently use
string encapsulated values for json output.

While at it, convert an unnecesary f-string to str().

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

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>