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author | Paolo Valente <paolo.valente@linaro.org> | 2017-08-31 21:00:30 +0300 |
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committer | Jens Axboe <axboe@kernel.dk> | 2017-08-31 22:55:25 +0300 |
commit | 233f0bf415e28adca96f61289e424ce4cfa9a9c0 (patch) | |
tree | 00330826c9febe0f105d3ea39f110a8a1f58c3f8 /Documentation/block | |
parent | 43cade803ebeb002403d4b704e041ce800e5b0e1 (diff) | |
download | linux-233f0bf415e28adca96f61289e424ce4cfa9a9c0.tar.xz |
doc, block, bfq: fix some typos and remove stale stuff
In addition to containing some typos and stale sentences, the file
bfq-iosched.txt still mentioned a set of sysfs parameters that have
been removed from this version of bfq. This commit fixes all these
issues.
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Reviewed-by: Jeremy Hickman <jeremywh7@gmail.com>
Reviewed-by: Laurentiu Nicola <lnicola@dend.ro>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'Documentation/block')
-rw-r--r-- | Documentation/block/bfq-iosched.txt | 66 |
1 files changed, 10 insertions, 56 deletions
diff --git a/Documentation/block/bfq-iosched.txt b/Documentation/block/bfq-iosched.txt index 05e2822a80b3..03ff4cc79911 100644 --- a/Documentation/block/bfq-iosched.txt +++ b/Documentation/block/bfq-iosched.txt @@ -16,14 +16,16 @@ throughput. So, when needed for achieving a lower latency, BFQ builds schedules that may lead to a lower throughput. If your main or only goal, for a given device, is to achieve the maximum-possible throughput at all times, then do switch off all low-latency heuristics -for that device, by setting low_latency to 0. Full details in Section 3. +for that device, by setting low_latency to 0. See Section 3 for +details on how to configure BFQ for the desired tradeoff between +latency and throughput, or on how to maximize throughput. On average CPUs, the current version of BFQ can handle devices performing at most ~30K IOPS; at most ~50 KIOPS on faster CPUs. As a reference, 30-50 KIOPS correspond to very high bandwidths with sequential I/O (e.g., 8-12 GB/s if I/O requests are 256 KB large), and -to 120-200 MB/s with 4KB random I/O. BFQ has not yet been tested on -multi-queue devices. +to 120-200 MB/s with 4KB random I/O. BFQ is currently being tested on +multi-queue devices too. The table of contents follow. Impatients can just jump to Section 3. @@ -154,10 +156,10 @@ plus a lot of code, are borrowed from CFQ. - With respect to idling for service guarantees, if several processes are competing for the device at the same time, but - all processes (and groups, after the following commit) have - the same weight, then BFQ guarantees the expected throughput - distribution without ever idling the device. Throughput is - thus as high as possible in this common scenario. + all processes and groups have the same weight, then BFQ + guarantees the expected throughput distribution without ever + idling the device. Throughput is thus as high as possible in + this common scenario. - If low-latency mode is enabled (default configuration), BFQ executes some special heuristics to detect interactive and soft @@ -191,10 +193,7 @@ plus a lot of code, are borrowed from CFQ. - Queues are scheduled according to a variant of WF2Q+, named B-WF2Q+, and implemented using an augmented rb-tree to preserve an O(log N) overall complexity. See [2] for more details. B-WF2Q+ is - also ready for hierarchical scheduling. However, for a cleaner - logical breakdown, the code that enables and completes - hierarchical support is provided in the next commit, which focuses - exactly on this feature. + also ready for hierarchical scheduling, details in Section 4. - B-WF2Q+ guarantees a tight deviation with respect to an ideal, perfectly fair, and smooth service. In particular, B-WF2Q+ @@ -427,51 +426,6 @@ Read-only parameter, used to show the weights of the currently active BFQ queues. -wr_ tunables ------------- - -BFQ exports a few parameters to control/tune the behavior of -low-latency heuristics. - -wr_coeff - -Factor by which the weight of a weight-raised queue is multiplied. If -the queue is deemed soft real-time, then the weight is further -multiplied by an additional, constant factor. - -wr_max_time - -Maximum duration of a weight-raising period for an interactive task -(ms). If set to zero (default value), then this value is computed -automatically, as a function of the peak rate of the device. In any -case, when the value of this parameter is read, it always reports the -current duration, regardless of whether it has been set manually or -computed automatically. - -wr_max_softrt_rate - -Maximum service rate below which a queue is deemed to be associated -with a soft real-time application, and is then weight-raised -accordingly (sectors/sec). - -wr_min_idle_time - -Minimum idle period after which interactive weight-raising may be -reactivated for a queue (in ms). - -wr_rt_max_time - -Maximum weight-raising duration for soft real-time queues (in ms). The -start time from which this duration is considered is automatically -moved forward if the queue is detected to be still soft real-time -before the current soft real-time weight-raising period finishes. - -wr_min_inter_arr_async - -Minimum period between I/O request arrivals after which weight-raising -may be reactivated for an already busy async queue (in ms). - - 4. Group scheduling with BFQ ============================ |