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docs: block/bfq: describe per-device weight

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The functionality of setting per-device weight for BFQ was added
in v5.4 (commit 795fe54c2a), but the documentation was never
updated.

While at it, improve formatting a bit.

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
Link: https://lore.kernel.org/r/20210614214109.207430-1-kolyshkin@gmail.com
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Kir Kolyshkin 2021-06-14 14:41:09 -07:00 • committed by Jens Axboe
parent a72c374f97
commit fda0b5ba9d
1 changed files with 27 additions and 11 deletions
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28
Documentation/block/bfq-iosched.rst
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@ -553,14 +553,21 @@ throughput sustainable with bfq, because updating the blkio.bfq.*
stats is rather costly, especially for some of the stats enabled by stats is rather costly, especially for some of the stats enabled by
CONFIG_BFQ_CGROUP_DEBUG. CONFIG_BFQ_CGROUP_DEBUG.
Parameters to set Parameters
----------------- ----------
For each group, there is only the following parameter to set. For each group, the following parameters can be set:
weight (namely blkio.bfq.weight or io.bfq-weight): the weight of the weight
group inside its parent. Available values: 1..1000 (default 100). The This specifies the default weight for the cgroup inside its parent.
linear mapping between ioprio and weights, described at the beginning Available values: 1..1000 (default: 100).
For cgroup v1, it is set by writing the value to `blkio.bfq.weight`.
For cgroup v2, it is set by writing the value to `io.bfq.weight`.
(with an optional prefix of `default` and a space).
The linear mapping between ioprio and weights, described at the beginning
of the tunable section, is still valid, but all weights higher than of the tunable section, is still valid, but all weights higher than
IOPRIO_BE_NR*10 are mapped to ioprio 0. IOPRIO_BE_NR*10 are mapped to ioprio 0.
@ -568,6 +575,15 @@ Recall that, if low-latency is set, then BFQ automatically raises the
weight of the queues associated with interactive and soft real-time weight of the queues associated with interactive and soft real-time
applications. Unset this tunable if you need/want to control weights. applications. Unset this tunable if you need/want to control weights.
weight_device
This specifies a per-device weight for the cgroup. The syntax is
`minor:major weight`. A weight of `0` may be used to reset to the default
weight.
For cgroup v1, it is set by writing the value to `blkio.bfq.weight_device`.
For cgroup v2, the file name is `io.bfq.weight`.
[1] [1]
P. Valente, A. Avanzini, "Evolution of the BFQ Storage I/O P. Valente, A. Avanzini, "Evolution of the BFQ Storage I/O