Re: [PATCH 2/4] Add tools/tests/offline_module

[Don Slutz <dslutz@verizon.com>]

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On 12/12/13 06:09, David Vrabel wrote:
> On 12/12/13 10:01, Ian Campbell wrote:
>> >On Wed, 2013-12-11 at 19:56 -0500, Don Slutz wrote:
>>> >>From: Don Slutz<dslutz@verizon.com>
>>> >>
>>> >>This is a quick and dirty linux kernel module to offline some cpus
>>> >>as far as Xen knows.
>>> >>
>>> >>This can be used to re-create the bug in hvm_save_one about
>>> >>returning the wrong data.
>> >
>> >Can this not be done via /sys/devices/system/cpu/cpu1/online etc?
>> >Documentation/cpu-hotplug.txt seems to suggest it can.
> Yes it can.
>
> echo 0 > /sys/devices/system/cpu/cpuN/online
>
> And onlined again with 1.
>
> David
I had forgotten about that when I was testing.  At least on 2.6.18-128.el5, cpu 0 does not work:

[root@P-8-0 ~]# echo 0 > /sys/devices/system/cpu/cpu0/online
-bash: /sys/devices/system/cpu/cpu0/online: Permission denied
[root@P-8-0 ~]# id
uid=0(root) gid=0(root) groups=0(root),1(bin),2(daemon),3(sys),4(adm),6(disk),10(wheel) context=root:system_r:unconfined_t:SystemLow-SystemHigh
[root@P-8-0 ~]# echo 0 > /sys/devices/system/cpu/cpu1/online
[root@P-8-0 ~]# echo 0 > /sys/devices/system/cpu/cpu3/online
[root@P-8-0 ~]# echo 0 > /sys/devices/system/cpu/cpu5/online
[root@P-8-0 ~]# echo 0 > /sys/devices/system/cpu/cpu7/online

And making cpu 0 offline was something I wanted to test.
    -Don Slutz

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