linux-kernel - Re: [PATCH v10 16/24] x86/resctrl: Add interface to the assign counter

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Message-ID: <7db76395-9bc0-4b26-942a-a354d5e3ff45@amd.com>
Date: Thu, 19 Dec 2024 15:38:08 -0600
From: "Moger, Babu" <bmoger@....com>
To: Reinette Chatre <reinette.chatre@...el.com>,
 "Luck, Tony" <tony.luck@...el.com>, Babu Moger <babu.moger@....com>
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Subject: Re: [PATCH v10 16/24] x86/resctrl: Add interface to the assign
 counter

Hi Reinette,

On 12/19/2024 3:12 PM, Reinette Chatre wrote:
> Hi Babu,
> 
> On 12/19/24 11:45 AM, Moger, Babu wrote:
>> Hi Reinette,
>>
>> On 12/18/2024 4:01 PM, Reinette Chatre wrote:
>>>
>>>
>>> On 12/13/24 8:54 AM, Moger, Babu wrote:
>>>> On 12/13/2024 10:24 AM, Luck, Tony wrote:
>>>>>> It is right thing to continue assignment if one of the domain is out of
>>>>>> counters. In that case how about we save the error(say error_domain) and
>>>>>> continue. And finally return success if both ret and error_domain are zeros.
>>>>>>
>>>>>>       return ret ?  ret : error_domain:
>>>>>
>>>>> If there are many domains, then you might have 3 succeed and 5 fail.
>>>>>
>>>>> I think the best you can do is return success if everything succeeded
>>>>> and an error if any failed.
>>>>
>>>> Yes. The above check should take care of this case.
>>>>
>>>
>>> If I understand correctly "error_domain" can capture the ID of
>>> a single failing domain. If there are multiple failing domains like
>>> in Tony's example then "error_domain" will not be accurate and thus
>>> can never be trusted. Instead of a single check of a failure user
>>> space is then forced to parse the more complex "mbm_assign_control"
>>> file to learn what succeeded and failed.
>>>
>>> Would it not be simpler to process sequentially and then fail on
>>> first error encountered with detailed error message? With that
>>> user space can determine exactly which portion of request
>>> succeeded and which portion failed.
>>
>> One more option is to print the error for each failure and continue. And finally return error.
>>
>> "Group mon1, domain:1 Out of MBM counters"
>>
>> We have the error information as well as the convenience of assignment on domains where counters are available when user is working with "*"(all domains).
> 
> This may be possible. Please keep in mind that any errors have to be
> easily consumed in an automated way to support the user space tools
> that interact with resctrl. I do not think we have thus far focused
> on the "last_cmd_status" buffer as part of the user space ABI so this opens
> up more considerations.
> 
> At this time the error handling of "all domains" does not seem to be
> consistent and obvious to user space. From what I can tell the
> implementation continues on to the next domain if one domain is out
> of counters but it exits immediately if a counter cannot be configured
> on a particular domain.

Yes. We can handle both the errors in the same way.

> 
>>
>> Note: I will be out of office starting next week Until Jan 10.
> 
> Thank you for letting me know. I am currently reviewing this series
> and will post feedback by tomorrow.

Sure. Thanks. I will try to get to some of it at least. The review 
comments which needs investigation may have to wait. Lets see.

Thanks
Babu