blob: 90343eb061199239f376c825d4d768e1b007a1ee (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
|
Instructions & guidelines to use Linux CPU hotplug
==================================================
A Introduction
This note describes how the Virtualizer software should
be configured for use with the Linux CPU hotplug
subsystem. It also mentions conditions that both Linux
and the Virtualizer software should fulfil for cpu
hotplug to work.
B Guidelines
A CPU hotplug operation involves migration of all tasks
and interrupts from the CPU in question before flushing
the relevant cache level(s) and shutting down the CPU.
A CPU is shutdown by programming the relevant RST_HOLDx
register in the KingFisher System Control Block (KFSCB).
The Virtualizer software traps accesses to the KFSCB made
by Linux to shutdown a CPU to save its HYP mode context
and request the Secure world to save its own context. It
then proceeds with the shutdown operation as Linux
originally intended. The key assumption made here is that
Linux will access the KFSCB RST_HOLDx registers only
during a CPU hotplug operation.
It is also assumed that its not possible to hotplug CPU0.
Hence, Linux CPU hotplug will work only with the MPx4
variant of the big.LITTLE FastModels. The CPU choice here
isn't prescriptive and does not imply that CPU0 should
always be the last man standing CPU in a hotplug capable
system. It was chosen for simplicity.
The Virtualizer software is built to switch the payload
software between clusters asynchronously. There is a
possibility of unpredictable behaviour happening if a
cluster switch is initiated when a CPU hotplug operation
is in progress. Hence the following two conditions need
to be met to be able to use the Virtualizer software in
conjunction with Linux CPU hotplug:
1. The Virtualizer software must be built to support
synchronous switching by setting the ASYNC
environment variable to FALSE prior to building it.
For example with the tcsh shell:
setenv ASYNC FALSE; make
2. Linux should invoke a cluster switch explicitly
after ensuring that no CPU hotplug operation is in
progress and vice versa. It can invoke a cluster
switch by using the "HVC #1" assembler instruction
from the relevant code.
C Instructions
1. Build a linux kernel as per the steps listed in
"docs/03-Linux-kernel-build.txt".
The configuration includes support for CPU
hotplug by default.
2. Use an existing root filesystem or build a new
one as per the steps listed in
"docs/06-Optional-rootfs-build.txt".
3. Place the kernel in the
"bootwrapper/payload/kernel" directory and the
filesystem in the "bootwrapper/payload/fsimg"
directory. Build the Virtualizer software with
support for synchronous switching as mentioned
in B.1.
4. Boot the resulting "bootwrapper/img.axf" file
using the "bootwrapper/big-little-mp4.mxscript"
file. At the command prompt, the Linux cpu
hotplug commands to hotplug CPUs should work
as expected. For example, to hotplug CPU1 do:
echo 0 > /sys/devices/system/cpu/cpu1/online
To bring CPU1 online do:
echo 1 > /sys/devices/system/cpu/cpu1/online
|
