Commit fda0b5ba authored by Kir Kolyshkin's avatar Kir Kolyshkin Committed by Jens Axboe
Browse files

docs: block/bfq: describe per-device weight 



The functionality of setting per-device weight for BFQ was added
in v5.4 (commit 795fe54c), but the documentation was never
updated.

While at it, improve formatting a bit.

Signed-off-by: default avatarKir Kolyshkin <kolyshkin@gmail.com>
Link: https://lore.kernel.org/r/20210614214109.207430-1-kolyshkin@gmail.com


Acked-by: default avatarTejun Heo <tj@kernel.org>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent a72c374f

Documentation/block/bfq-iosched.rst

+27 −11
Original line number Diff line number Diff line
@@ -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

CONFIG_BFQ_CGROUP_DEBUG.



Parameters to set

-----------------

Parameters

----------



For each group, the following parameters can be set:



  weight

        This specifies the default weight for the cgroup inside its parent.

        Available values: 1..1000 (default: 100).



For each group, there is only the following parameter to set.

        For cgroup v1, it is set by writing the value to `blkio.bfq.weight`.



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

        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.
@@ -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

        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]

    P. Valente, A. Avanzini, "Evolution of the BFQ Storage I/O