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[ Upstream commit 8c772a9bfc7c07c76f4a58b58910452fbb20843b ]
Our test reported the following stack, and vmcore showed that
->inflight counter is -1.
[ffffc9003fcc38d0] __schedule at ffffffff8173d95d
[ffffc9003fcc3958] schedule at ffffffff8173de26
[ffffc9003fcc3970] io_schedule at ffffffff810bb6b6
[ffffc9003fcc3988] blkcg_iolatency_throttle at ffffffff813911cb
[ffffc9003fcc3a20] rq_qos_throttle at ffffffff813847f3
[ffffc9003fcc3a48] blk_mq_make_request at ffffffff8137468a
[ffffc9003fcc3b08] generic_make_request at ffffffff81368b49
[ffffc9003fcc3b68] submit_bio at ffffffff81368d7d
[ffffc9003fcc3bb8] ext4_io_submit at ffffffffa031be00 [ext4]
[ffffc9003fcc3c00] ext4_writepages at ffffffffa03163de [ext4]
[ffffc9003fcc3d68] do_writepages at ffffffff811c49ae
[ffffc9003fcc3d78] __filemap_fdatawrite_range at ffffffff811b6188
[ffffc9003fcc3e30] filemap_write_and_wait_range at ffffffff811b6301
[ffffc9003fcc3e60] ext4_sync_file at ffffffffa030cee8 [ext4]
[ffffc9003fcc3ea8] vfs_fsync_range at ffffffff8128594b
[ffffc9003fcc3ee8] do_fsync at ffffffff81285abd
[ffffc9003fcc3f18] sys_fsync at ffffffff81285d50
[ffffc9003fcc3f28] do_syscall_64 at ffffffff81003c04
[ffffc9003fcc3f50] entry_SYSCALL_64_after_swapgs at ffffffff81742b8e
The ->inflight counter may be negative (-1) if
1) blk-iolatency was disabled when the IO was issued,
2) blk-iolatency was enabled before this IO reached its endio,
3) the ->inflight counter is decreased from 0 to -1 in endio()
In fact the hang can be easily reproduced by the below script,
H=/sys/fs/cgroup/unified/
P=/sys/fs/cgroup/unified/test
echo "+io" > $H/cgroup.subtree_control
mkdir -p $P
echo $$ > $P/cgroup.procs
xfs_io -f -d -c "pwrite 0 4k" /dev/sdg
echo "`cat /sys/block/sdg/dev` target=1000000" > $P/io.latency
xfs_io -f -d -c "pwrite 0 4k" /dev/sdg
This fixes the problem by freezing the queue so that while
enabling/disabling iolatency, there is no inflight rq running.
Note that quiesce_queue is not needed as this only updating iolatency
configuration about which dispatching request_queue doesn't care.
Signed-off-by: Liu Bo <bo.liu@linux.alibaba.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
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Currently, avg_lat is calculated by accumulating the mean of every
window in a long running cumulative average. As time goes on, the metric
becomes less and less useful due to the accumulated history.
This patch reuses the same calculation done in load averages to make the
avg_lat metric more lively. Unlike load averages, the avg only advances
when a window elapses (due to an io). Idle periods extend the most
recent window. Bucketing is used to limit the history of avg_lat by
binding it to the window size. So, the window range for 1/exp (decay
rate) is [1 min, 2.5 min) when windows elapse immediately.
The current sample window size is exposed in the debug info to enable
calculation of the window range.
Signed-off-by: Dennis Zhou <dennisszhou@gmail.com>
Acked-by: Tejun Heo <tj@kernel.org>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
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At this point we have a ref on the blkg, we need to drop it if we don't
have a iolat.
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
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In our longer tests we noticed that some boxes would degrade to the
point of uselessness. This is because we truncate the current time when
saving it in our bio, but I was using the raw current time to subtract
from. So once the box had been up a certain amount of time it would
appear as if our IO's were taking several years to complete. Fix this
by truncating the current time so it matches the issue time. Verified
this worked by running with this patch for a week on our test tier.
Signed-off-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
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Early versions of these patches had us waiting for seconds at a time
during submission, so we had to adjust the timing window we monitored
for latency. Now we don't do things like that so this is unnecessary
code.
Signed-off-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
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max_depth used to be a u64, but I changed it to a unsigned int but
didn't convert my comparisons over everywhere. Fix by using UINT_MAX
everywhere instead of (u64)-1.
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
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On 32-bit architectures, dividing a 64-bit number needs to use the
do_div() function or something like it to avoid a link failure:
block/blk-iolatency.o: In function `iolatency_prfill_limit':
blk-iolatency.c:(.text+0x8cc): undefined reference to `__aeabi_uldivmod'
Using div_u64() gives us the best output and avoids the need for an
explicit cast.
Fixes: d70675121546 ("block: introduce blk-iolatency io controller")
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
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Current IO controllers for the block layer are less than ideal for our
use case. The io.max controller is great at hard limiting, but it is
not work conserving. This patch introduces io.latency. You provide a
latency target for your group and we monitor the io in short windows to
make sure we are not exceeding those latency targets. This makes use of
the rq-qos infrastructure and works much like the wbt stuff. There are
a few differences from wbt
- It's bio based, so the latency covers the whole block layer in addition to
the actual io.
- We will throttle all IO types that comes in here if we need to.
- We use the mean latency over the 100ms window. This is because writes can
be particularly fast, which could give us a false sense of the impact of
other workloads on our protected workload.
- By default there's no throttling, we set the queue_depth to INT_MAX so that
we can have as many outstanding bio's as we're allowed to. Only at
throttle time do we pay attention to the actual queue depth.
- We backcharge cgroups for root cg issued IO and induce artificial
delays in order to deal with cases like metadata only or swap heavy
workloads.
In testing this has worked out relatively well. Protected workloads
will throttle noisy workloads down to 1 io at time if they are doing
normal IO on their own, or induce up to a 1 second delay per syscall if
they are doing a lot of root issued IO (metadata/swap IO).
Our testing has revolved mostly around our production web servers where
we have hhvm (the web server application) in a protected group and
everything else in another group. We see slightly higher requests per
second (RPS) on the test tier vs the control tier, and much more stable
RPS across all machines in the test tier vs the control tier.
Another test we run is a slow memory allocator in the unprotected group.
Before this would eventually push us into swap and cause the whole box
to die and not recover at all. With these patches we see slight RPS
drops (usually 10-15%) before the memory consumer is properly killed and
things recover within seconds.
Signed-off-by: Josef Bacik <jbacik@fb.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
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Liu Bo
Dennis Zhou (Facebook)
Josef Bacik
Josef Bacik
Arnd Bergmann