[PATCH 1/3] docs: block/bfq: describe per-device weight
From: Kir Kolyshkin <hidden>
Date: 2021-06-11 03:07:52
Also in:
linux-doc
Subsystem:
bfq i/o scheduler, block layer, documentation, the rest · Maintainers:
Yu Kuai, Jens Axboe, Jonathan Corbet, Linus Torvalds
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 <redacted> --- Documentation/block/bfq-iosched.rst | 38 ++++++++++++++++++++--------- 1 file changed, 27 insertions(+), 11 deletions(-)
diff --git a/Documentation/block/bfq-iosched.rst b/Documentation/block/bfq-iosched.rst
index 66c5a4e54130..7200152c461e 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 cat 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`. [1]
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2.31.1