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authorPaolo Valente <paolo.valente@linaro.org>2017-08-31 21:00:30 +0300
committerJens Axboe <axboe@kernel.dk>2017-08-31 22:55:25 +0300
commit233f0bf415e28adca96f61289e424ce4cfa9a9c0 (patch)
tree00330826c9febe0f105d3ea39f110a8a1f58c3f8 /Documentation/block
parent43cade803ebeb002403d4b704e041ce800e5b0e1 (diff)
downloadlinux-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.txt66
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
============================