linux-kernel - Re: [PATCH v11 16/23] x86/resctrl: Add the functionality to unassigm MBM events

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Message-ID: <075faedf-4c1c-4762-be82-2dc6280fab98@amd.com>
Date: Fri, 21 Feb 2025 18:36:40 -0600
From: "Moger, Babu" <bmoger@....com>
To: Reinette Chatre <reinette.chatre@...el.com>, babu.moger@....com,
 corbet@....net, tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
 dave.hansen@...ux.intel.com, tony.luck@...el.com, peternewman@...gle.com
Cc: x86@...nel.org, hpa@...or.com, paulmck@...nel.org,
 akpm@...ux-foundation.org, thuth@...hat.com, rostedt@...dmis.org,
 xiongwei.song@...driver.com, pawan.kumar.gupta@...ux.intel.com,
 daniel.sneddon@...ux.intel.com, jpoimboe@...nel.org, perry.yuan@....com,
 sandipan.das@....com, kai.huang@...el.com, xiaoyao.li@...el.com,
 seanjc@...gle.com, xin3.li@...el.com, andrew.cooper3@...rix.com,
 ebiggers@...gle.com, mario.limonciello@....com, james.morse@....com,
 tan.shaopeng@...itsu.com, linux-doc@...r.kernel.org,
 linux-kernel@...r.kernel.org, maciej.wieczor-retman@...el.com,
 eranian@...gle.com
Subject: Re: [PATCH v11 16/23] x86/resctrl: Add the functionality to unassigm
 MBM events

Hi Reinette,

On 2/10/2025 12:30 PM, Reinette Chatre wrote:
> Hi Babu,
> 
> On 2/10/25 8:23 AM, Moger, Babu wrote:
>> Hi Reinette,
>>
>> On 2/5/25 21:54, Reinette Chatre wrote:
>>> Hi Babu,
>>>
>>> subject: unassigm -> unassign
>>
>> Sure.
>>
>>>
>>> On 1/22/25 12:20 PM, Babu Moger wrote:
>>>> The mbm_cntr_assign mode provides a limited number of hardware counters
>>>
>>> (now back to "limited number of hardware counters")
>>
>> How about?
>>
>> The mbm_cntr_assign mode provides "num_mbm_cntrs" number of hardware counters
> 
> ok.
> 
>>
>>>
>>>> that can be assigned to an RMID, event pair to monitor bandwidth while
>>>> assigned. If all counters are in use, the kernel will show an error
>>>> message: "Out of MBM assignable counters" when a new assignment is
>>>> requested. To make space for a new assignment, users must unassign an
>>>
>>> To me "kernel will show an error" implies the kernel ring buffer. Please make
>>> the message accurate and mention that it will be in
>>> last_cmd_status while also considering to use -ENOSPC to help user space.
>>
>> If all the counters are in use, the kernel will log the error message
>> "Unable to allocate counter in domain" in /sys/fs/resctrl/info/
>> last_cmd_status when a new assignment is requested. To make space for a
>> new assignment, users must unassign an already assigned counter and retry
>> the assignment again.
>>
> 
> This is better, but can user space receive -ENOSPC to avoid needing to check
> and parse last_cmd_status on every error?

Yes. There was a problem in passing the error in 
resctrl_process_flags(). Took care of it now.

Thanks
Babu