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[PATCH BUGFIX/IMPROVEMENT 0/2] doc, block, bfq: improve documentation on how to to properly configure bfq

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  [PATCH BUGFIX/IMPROVEMENT 0/2] doc, block, bfq: improve documentation on how to to properly configure bfq Paolo Valente <paolo.valente@linaro.org> - 2017-08-31 20:10 +0200
    [PATCH BUGFIX/IMPROVEMENT 1/2] doc, block, bfq: fix some typos and remove stale stuff Paolo Valente <paolo.valente@linaro.org> - 2017-08-31 20:10 +0200
    Re: [PATCH BUGFIX/IMPROVEMENT 0/2] doc, block, bfq: improve  documentation on how to to properly configure bfq Jens Axboe <axboe@kernel.dk> - 2017-08-31 22:00 +0200

#1724472 — [PATCH BUGFIX/IMPROVEMENT 0/2] doc, block, bfq: improve documentation on how to to properly configure bfq

Many users have reported the lack of an HOWTO for properly configuring
bfq as a function of the goal one wants to achieve (max
responsiveness, max throughput, ...). The second patch in this
two-patch series addresses this issue by improving the file
bfq-iosched.txt in such a way that it also provides some guidance on
this task. The first patch fixes some issues that I have found while
working on the file.

Thanks,
Paolo

Paolo Valente (2):
  doc, block, bfq: fix some typos and remove stale stuff
  doc, block, bfq: better describe how to properly configure bfq

 Documentation/block/bfq-iosched.txt | 144 ++++++++++++++++--------------------
 1 file changed, 64 insertions(+), 80 deletions(-)

--
2.10.0

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#1724473 — [PATCH BUGFIX/IMPROVEMENT 1/2] 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>
---
 Documentation/block/bfq-iosched.txt | 66 ++++++-------------------------------
 1 file changed, 10 insertions(+), 56 deletions(-)

diff --git a/Documentation/block/bfq-iosched.txt b/Documentation/block/bfq-iosched.txt
index 05e2822..03ff4cc 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
 ============================
 
-- 
2.10.0

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#1724545 — Re: [PATCH BUGFIX/IMPROVEMENT 0/2] doc, block, bfq: improve documentation on how to to properly configure bfq

On 08/31/2017 12:00 PM, Paolo Valente wrote:
> Many users have reported the lack of an HOWTO for properly configuring
> bfq as a function of the goal one wants to achieve (max
> responsiveness, max throughput, ...). The second patch in this
> two-patch series addresses this issue by improving the file
> bfq-iosched.txt in such a way that it also provides some guidance on
> this task. The first patch fixes some issues that I have found while
> working on the file.

Applied for 4.14, thanks Paolo.

-- 
Jens Axboe

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