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authorKir Kolyshkin <kolyshkin@gmail.com>2021-06-15 00:41:09 +0300
committerJens Axboe <axboe@kernel.dk>2021-06-16 20:31:24 +0300
commitfda0b5ba9d5a9f6bfab9bc195f7a8fce13aedf61 (patch)
treeac6ff00da348051781fc017ddd645b69287e47b5 /Documentation/block/bfq-iosched.rst
parenta72c374f97a4c7b2f9dde5144c867fec4bdcd798 (diff)
downloadlinux-fda0b5ba9d5a9f6bfab9bc195f7a8fce13aedf61.tar.xz
docs: block/bfq: describe per-device weight
The functionality of setting per-device weight for BFQ was added in v5.4 (commit 795fe54c2a828099), 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>
Diffstat (limited to 'Documentation/block/bfq-iosched.rst')
-rw-r--r--Documentation/block/bfq-iosched.rst38
1 files changed, 27 insertions, 11 deletions
diff --git a/Documentation/block/bfq-iosched.rst b/Documentation/block/bfq-iosched.rst
index 66c5a4e54130..df3a8a47f58c 100644
--- a/Documentation/block/bfq-iosched.rst
+++ b/Documentation/block/bfq-iosched.rst
@@ -553,20 +553,36 @@ throughput sustainable with bfq, because updating the blkio.bfq.*
stats is rather costly, especially for some of the stats enabled by
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
-group inside its parent. Available values: 1..1000 (default 100). The
-linear mapping between ioprio and weights, described at the beginning
-of the tunable section, is still valid, but all weights higher than
-IOPRIO_BE_NR*10 are mapped to ioprio 0.
+ weight
+ This specifies the default weight for the cgroup inside its parent.
+ Available values: 1..1000 (default: 100).
-Recall that, if low-latency is set, then BFQ automatically raises the
-weight of the queues associated with interactive and soft real-time
-applications. Unset this tunable if you need/want to control weights.
+ 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
+ IOPRIO_BE_NR*10 are mapped to ioprio 0.
+
+ Recall that, if low-latency is set, then BFQ automatically raises the
+ weight of the queues associated with interactive and soft real-time
+ 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`.
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