PATCHES/patches/doc-block-bfq-update-max-IOPS-sustainable-with-BFQ.patch

From 68017e5d87a2477d40476f1a0a06f202ee79316b Mon Sep 17 00:00:00 2001
From: Paolo Valente <paolo.valente@linaro.org>
Date: Mon, 13 Nov 2017 07:34:07 +0100
Subject: [PATCH] doc, block, bfq: update max IOPS sustainable with BFQ

We have investigated more deeply the performance of BFQ, in terms of
number of IOPS that can be processed by the CPU when BFQ is used as
I/O scheduler. In more detail, using the script [1], we have measured
the number of IOPS reached on top of a null block device configured
with zero latency, as a function of the workload (sequential read,
sequential write, random read, random write) and of the system (we
considered desktops, laptops and embedded systems).

Basing on the resulting figures, with this commit we update the
current, conservative IOPS range reported in BFQ documentation. In
particular, the documentation now reports, for each of three different
systems, the lowest number of IOPS obtained for that system with the
above test (namely, the value obtained with the workload leading to
the lowest IOPS).

[1] https://github.com/Algodev-github/IOSpeed

Reviewed-by: Lee Tibbert <lee.tibbert@gmail.com>
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Luca Miccio <lucmiccio@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 Documentation/block/bfq-iosched.txt | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/Documentation/block/bfq-iosched.txt b/Documentation/block/bfq-iosched.txt
index 3d6951d63489..7a9361508157 100644
--- a/Documentation/block/bfq-iosched.txt
+++ b/Documentation/block/bfq-iosched.txt
@@ -20,12 +20,17 @@ 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 is currently being tested on
-multi-queue devices too.
+BFQ has a non-null overhead, which limits the maximum IOPS that the
+CPU can process for a device scheduled with BFQ. To give an idea of
+the limits on slow or average CPUs, here are BFQ limits for three
+different CPUs, on, respectively, an average laptop, an old desktop,
+and a cheap embedded system, in case full hierarchical support is
+enabled (i.e., CONFIG_BFQ_GROUP_IOSCHED is set):
+- Intel i7-4850HQ: 250 KIOPS
+- AMD A8-3850: 170 KIOPS
+- ARM CortexTM-A53 Octa-core: 45 KIOPS
+
+BFQ works for multi-queue devices too.
 
 The table of contents follow. Impatients can just jump to Section 3.
 
-- 
2.13.6

1	From 68017e5d87a2477d40476f1a0a06f202ee79316b Mon Sep 17 00:00:00 2001
2	From: Paolo Valente <paolo.valente@linaro.org>
3	Date: Mon, 13 Nov 2017 07:34:07 +0100
4	Subject: [PATCH] doc, block, bfq: update max IOPS sustainable with BFQ
5
6	We have investigated more deeply the performance of BFQ, in terms of
7	number of IOPS that can be processed by the CPU when BFQ is used as
8	I/O scheduler. In more detail, using the script [1], we have measured
9	the number of IOPS reached on top of a null block device configured
10	with zero latency, as a function of the workload (sequential read,
11	sequential write, random read, random write) and of the system (we
12	considered desktops, laptops and embedded systems).
13
14	Basing on the resulting figures, with this commit we update the
15	current, conservative IOPS range reported in BFQ documentation. In
16	particular, the documentation now reports, for each of three different
17	systems, the lowest number of IOPS obtained for that system with the
18	above test (namely, the value obtained with the workload leading to
19	the lowest IOPS).
20
21	[1] https://github.com/Algodev-github/IOSpeed
22
23	Reviewed-by: Lee Tibbert <lee.tibbert@gmail.com>
24	Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
25	Signed-off-by: Luca Miccio <lucmiccio@gmail.com>
26	Signed-off-by: Jens Axboe <axboe@kernel.dk>
27	---
28	Documentation/block/bfq-iosched.txt \| 17 +++++++++++------
29	1 file changed, 11 insertions(+), 6 deletions(-)
30
31	diff --git a/Documentation/block/bfq-iosched.txt b/Documentation/block/bfq-iosched.txt
32	index 3d6951d63489..7a9361508157 100644
33	--- a/Documentation/block/bfq-iosched.txt
34	+++ b/Documentation/block/bfq-iosched.txt
35	@@ -20,12 +20,17 @@ for that device, by setting low_latency to 0. See Section 3 for
36	details on how to configure BFQ for the desired tradeoff between
37	latency and throughput, or on how to maximize throughput.
38
39	-On average CPUs, the current version of BFQ can handle devices
40	-performing at most ~30K IOPS; at most ~50 KIOPS on faster CPUs. As a
41	-reference, 30-50 KIOPS correspond to very high bandwidths with
42	-sequential I/O (e.g., 8-12 GB/s if I/O requests are 256 KB large), and
43	-to 120-200 MB/s with 4KB random I/O. BFQ is currently being tested on
44	-multi-queue devices too.
45	+BFQ has a non-null overhead, which limits the maximum IOPS that the
46	+CPU can process for a device scheduled with BFQ. To give an idea of
47	+the limits on slow or average CPUs, here are BFQ limits for three
48	+different CPUs, on, respectively, an average laptop, an old desktop,
49	+and a cheap embedded system, in case full hierarchical support is
50	+enabled (i.e., CONFIG_BFQ_GROUP_IOSCHED is set):
51	+- Intel i7-4850HQ: 250 KIOPS
52	+- AMD A8-3850: 170 KIOPS
53	+- ARM CortexTM-A53 Octa-core: 45 KIOPS
54	+
55	+BFQ works for multi-queue devices too.
56
57	The table of contents follow. Impatients can just jump to Section 3.
58
59	--
60	2.13.6
61