[LTP] [PATCH] cpuset_hotplug_test/cpuset_hotplug: Fix bug for obtaining task_cpus value in root_cpu_hotplug_test

[xuyang2018.jy@fujitsu.com <xuyang2018.jy@fujitsu.com>]

Hi Samuel, Zou
> Hi,
>
> A friendly reminder for the two patchs in:
>
> https://patchwork.ozlabs.org/project/ltp/patch/1617707717-63693-1-git-send-email-zou_wei@huawei.com/
>
>
> https://patchwork.ozlabs.org/project/ltp/patch/1617701249-62196-1-git-send-email-zou_wei@huawei.com/
>
>
> Can someone please review the patchs, comment, and if appropriate commit
> them?
>
> Regards,
> Zou Wei
>
> On 2021/4/6 17:27, Zou Wei wrote:
>> --------------------------
>>
>> 1. The method of obtaining $task_cpus from root_cpu_hotplug_test is
>> incorrect, because the value of Cpus_allowed_list is related
>> to /sys/devices/system/cpu/possible and
>> /sys/devices/system/cpu/isolated.
>>
>> 2. If isolcpus is configured in cmdline, the value of
>> Cpus_allowed_list is equal to /sys/devices/system/cpu/possible minus
>> /sys/devices/system/cpu/isolated. In this case, $task_cpus is
>> inconsistent
>> with $expect_task_cpus, test will be failed.
>>
>> 3. Need to change the method of obtaining $task_cpu
>> from /sys/devices/system/cpu/present.
Thanks for your patch, I also met the same problem when 
/sys/devices/system/cpu/possible is not equal 
to/sys/devices/system/cpu/possible/present  .
Cpus_allowed_list:      0-511
but my present cpu is 0-103

Then I use possible_cpus==104 in /etc/defaut/grub, cpu_hotplug case then 
pass.

According to kernel documentation[1] and kernel fs/proc/array code[2](It 
just print cpu mask instead of present cpu), So using 
/sys/devices/system/cpu/present is right instead of getting cpu_allow_list.

possible: cpus that have been allocated resources and can be
		brought online if they are present.

present: cpus that have been identified as being present in
		the system.


Reviewed-by: Yang Xu <xuyang2018.jy@fujitsu.com>

[1]https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/ABI/testing/sysfs-devices-system-cpu
[2]https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/fs/proc/array.c#n418

ps:
Also find a kernel documentation problem and have sent a patch to remove 
non-existed cpu-hotplug.txt in admin-guide/cputopology.rst.


Best Regards
Yang Xu
>>
>> 4. The description of cpu_present_mask:
>> Bitmap of CPUs currently present in the system.
>> Not all of them may be online. When physical hotplug is processed
>> by the relevant subsystem (e.g ACPI) can change and new bit either be
>> added or removed from the map depending on the event is
>> hot-add/hot-remove. There are currently no locking rules as of now.
>> Typical usage is to init topology during boot,
>> at which time hotplug is disabled.
>>
>> Signed-off-by: Zou Wei <zou_wei@huawei.com>
>> ---
>> .../controllers/cpuset/cpuset_hotplug_test/cpuset_hotplug_test.sh | 3 +--
>> 1 file changed, 1 insertion(+), 2 deletions(-)
>>
>> diff --git
>> a/testcases/kernel/controllers/cpuset/cpuset_hotplug_test/cpuset_hotplug_test.sh
>> b/testcases/kernel/controllers/cpuset/cpuset_hotplug_test/cpuset_hotplug_test.sh
>>
>> index 155e536..2c6993a 100755
>> ---
>> a/testcases/kernel/controllers/cpuset/cpuset_hotplug_test/cpuset_hotplug_test.sh
>>
>> +++
>> b/testcases/kernel/controllers/cpuset/cpuset_hotplug_test/cpuset_hotplug_test.sh
>>
>> @@ -93,8 +93,7 @@ root_cpu_hotplug_test()
>> root_cpus="`cat $CPUSET/cpuset.cpus`"
>> - task_cpus="`cat /proc/$tst_pid/status | grep Cpus_allowed_list`"
>> - task_cpus="`echo $task_cpus | sed -e 's/Cpus_allowed_list: //'`"
>> + task_cpus="`cat /sys/devices/system/cpu/present`"
>> check_result "$root_cpus" "$expect_cpus"
>> ret=$?
>>
>