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Diffstat (limited to 'Documentation/block/bfq-iosched.rst')
| -rw-r--r-- | Documentation/block/bfq-iosched.rst | 49 |
1 files changed, 29 insertions, 20 deletions
diff --git a/Documentation/block/bfq-iosched.rst b/Documentation/block/bfq-iosched.rst index 0d237d402860..df3a8a47f58c 100644 --- a/Documentation/block/bfq-iosched.rst +++ b/Documentation/block/bfq-iosched.rst @@ -430,13 +430,13 @@ fifo_expire_async ----------------- This parameter is used to set the timeout of asynchronous requests. Default -value of this is 248ms. +value of this is 250ms. fifo_expire_sync ---------------- This parameter is used to set the timeout of synchronous requests. Default -value of this is 124ms. In case to favor synchronous requests over asynchronous +value of this is 125ms. In case to favor synchronous requests over asynchronous one, this value should be decreased relative to fifo_expire_async. low_latency @@ -492,13 +492,6 @@ set max_budget to higher values than those to which BFQ would have set it with auto-tuning. An alternative way to achieve this goal is to just increase the value of timeout_sync, leaving max_budget equal to 0. -weights -------- - -Read-only parameter, used to show the weights of the currently active -BFQ queues. - - 4. Group scheduling with BFQ ============================ @@ -560,20 +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..10000 (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] |