[SOLVED] Unable to shutdown CPU1

gnourt · 03-20-2018, 05:58 AM

Hi all,
I am trying to offline cpu1 in kernel by command line.But the kernel always reboot as when I try to do it.
"
root@mx6q:~# uname -a
Linux mx6q 3.14.79-01359-g7adf8276561f #1 SMP PREEMPT Thu Mar 15 07:41:39 CET 2018 armv7l GNU/Linux
root@mx6q:~#
root@mx6q:~# cat /proc/cpuinfo | grep processor
processor : 0
processor : 1
root@mx6q:~#
root@mx6q:~# echo 0 > /sys/devices/system/cpu/cpu1/online
Write failed: Broken pipe
"
Please give me some point to understand why it fail in this case.
I can not find any where to configure make cpu1 always online.
Thanks for help in advance.

keefaz · 03-21-2018, 05:15 PM

Have you 2 physical cpus or 1 multi core cpu ?

[edit]
Oh it's arm multicore? Maybe cores can not be put offline at runtime with arm
There is a kernel parameter: maxcpus=1
will limit the available cpu cores to 1

gnourt · 03-22-2018, 04:58 AM

Thanks for your help !! keefaz

yub , it's arm multicore .
But i'm not clear why we can not be put offline at runtime with arm.
At previous kernel version. I still put offline cpu1 but in this kernel i can not put offline it.
I guess that have option to allow on/off cpu1 but i can not find it.is it maxcpus ?How can we show exactly value of maxcpus by command line?

keefaz · 03-22-2018, 07:49 AM

maxcpus is a kernel parameter, you use it as a kernel boot option in bootloader (grub, lilo etc...)
https://static.lwn.net/kerneldoc/cor...u_hotplug.html

Note that you should still be able to put the cpu1 online later at runtime
(echo 1 > /sys/devices/system/cpu/cpu1/online)

Now if putting cpu offline worked in previous version, I would try to find out if there is a configuration change between the 2 versions

schneidz · 03-22-2018, 08:13 AM

i wonder what the output of this would yield:

Code:

[schneidz@hyper womens-health-challenge]$ egrep "processor|flags|physical|core" /proc/cpuinfo 
processor	: 0
physical id	: 0
core id		: 0
cpu cores	: 2
flags		: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx lm constant_tsc arch_perfmon pebs bts nopl cpuid aperfmperf pni dtes64 monitor ds_cpl tm2 ssse3 cx16 xtpr pdcm movbe lahf_lm dtherm
address sizes	: 32 bits physical, 48 bits virtual
processor	: 1
physical id	: 0
core id		: 1
cpu cores	: 2
flags		: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx lm constant_tsc arch_perfmon pebs bts nopl cpuid aperfmperf pni dtes64 monitor ds_cpl tm2 ssse3 cx16 xtpr pdcm movbe lahf_lm dtherm
address sizes	: 32 bits physical, 48 bits virtual
processor	: 2
physical id	: 0
core id		: 0
cpu cores	: 2
flags		: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx lm constant_tsc arch_perfmon pebs bts nopl cpuid aperfmperf pni dtes64 monitor ds_cpl tm2 ssse3 cx16 xtpr pdcm movbe lahf_lm dtherm
address sizes	: 32 bits physical, 48 bits virtual
processor	: 3
physical id	: 0
core id		: 1
cpu cores	: 2
flags		: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx lm constant_tsc arch_perfmon pebs bts nopl cpuid aperfmperf pni dtes64 monitor ds_cpl tm2 ssse3 cx16 xtpr pdcm movbe lahf_lm dtherm
address sizes	: 32 bits physical, 48 bits virtual

gnourt · 04-01-2018, 11:10 PM

Thanks you so much !
I'm not person who built kernel.so I don't know the changed between the 2 versions.
I'm trying to contact kernel team to give me the kernel's configuration.
We will continues discuss later.

gnourt · 04-08-2018, 09:24 PM

Hi,
This issue happen because there are some changes in kernel source related to cpuhotplug.
Thanks for your support.