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

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Message-ID: <1faef062-ed33-46da-9378-7a224dbee811@intel.com>
Date: Mon, 10 Feb 2025 10:30:46 -0800
From: Reinette Chatre <reinette.chatre@...el.com>
To: <babu.moger@....com>, <corbet@....net>, <tglx@...utronix.de>,
	<mingo@...hat.com>, <bp@...en8.de>, <dave.hansen@...ux.intel.com>,
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Subject: Re: [PATCH v11 16/23] x86/resctrl: Add the functionality to unassigm
 MBM events

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?

Reinette