Re: [RFC PATCH v3 17/17] x86/resctrl: Introduce interface to modify assignment states of the groups

Moger, Babu
2024-05-02T18:11:48Z

Hi Dave,

On 5/2/24 12:52, Reinette Chatre wrote:
> Hi Dave,
>
> On 5/2/2024 9:21 AM, Dave Martin wrote:
>> On Thu, Mar 28, 2024 at 08:06:50PM -0500, Babu Moger wrote:
>>> diff --git a/Documentation/arch/x86/resctrl.rst b/Documentation/arch/x86/resctrl.rst
>>> index 2d96565501ab..64ec70637c66 100644
>>> --- a/Documentation/arch/x86/resctrl.rst
>>> +++ b/Documentation/arch/x86/resctrl.rst
>>> @@ -328,6 +328,77 @@ with the following files:
>>> None of events are assigned on this mon group. This is a child
>>> monitor group of the non default control mon group.
>>>
>>> + Assignment state can be updated by writing to this interface.
>>> +
>>> + NOTE: Assignment on one domain applied on all the domains. User can
>>> + pass one valid domain and assignment will be updated on all the
>>> + available domains.
>>> +
>>> + Format is similar to the list format with addition of op-code for the
>>> + assignment operation.
>>> +
>>> + * Default CTRL_MON group:
>>> + "//<domain_id><op-code><assignment_flags>"
>>> +
>>> + * Non-default CTRL_MON group:
>>> + "<CTRL_MON group>//<domain_id><op-code><assignment_flags>"
>>> +
>>> + * Child MON group of default CTRL_MON group:
>>> + "/<MON group>/<domain_id><op-code><assignment_flags>"
>>> +
>>> + * Child MON group of non-default CTRL_MON group:
>>> + "<CTRL_MON group>/<MON group>/<domain_id><op-code><assignment_flags>"
>>
>> The final bullet seems to cover everything, if we allow <CTRL_MON group>
>> and <MON group> to be independently empty strings to indicate the
>> default control and/or monitoring group respectively.
>>
>> Would that be simpler than treating this as four separate cases?

That is correct. I will add a generic format before this description and
then add these 4 cases. That way it will be more clear.

>>
>> Also, will this go wrong if someone creates a resctrl group with '\n'
>> (i.e., a newline character) in the name?
>
> There is a check for this in rdtgroup_mkdir().
>
>>
>>> +
>>> + Op-code can be one of the following:
>>> + ::
>>> +
>>> + = Update the assignment to match the flags
>>> + + Assign a new state
>>> + - Unassign a new state
>>> + _ Unassign all the states
>>
>> I can't remember whether I already asked this, but is "_" really
>> needed here?
>
> Asked twice:
> https://lore.kernel.org/lkml/ZiaRXrmDDjc194JI@e133380.arm.com/
> https://lore.kernel.org/lkml/ZiervIprcwoApAqw@e133380.arm.com/
>
> Answered:
> https://lore.kernel.org/lkml/4cd220cc-2e8e-4193-b01a-d3cd798c7118@amd.com/
>
> You seemed ok with answer then:
> https://lore.kernel.org/lkml/ZiffF93HM8bE3qo7@e133380.arm.com/
>
>>
>> Wouldn't it be the case that
>>
>> //*_
>>
>> would mean just the same thing as
>>
>> //*=_
>>
>> ...? (assuming the "*" = "all domains" convention already discussed)
>>
>> Maybe I'm missing something here.
>
> I believe have an explicit operator ("+", "=", or "-") simplifies
> parsing while providing an interface consistent with what users are already
> used to.
>
> Reinette

--
Thanks
Babu Moger