linux-kernel - Re: [PATCH v2 00/17] x86/resctrl : Support AMD Assignable Bandwidth Monitoring Counters (ABMC)

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Date: Fri, 23 Feb 2024 14:11:15 -0600
From: "Moger, Babu" <babu.moger@....com>
To: Reinette Chatre <reinette.chatre@...el.com>,
 James Morse <james.morse@....com>, corbet@....net, fenghua.yu@...el.com,
 tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
 dave.hansen@...ux.intel.com
Cc: x86@...nel.org, hpa@...or.com, paulmck@...nel.org, rdunlap@...radead.org,
 tj@...nel.org, peterz@...radead.org, yanjiewtw@...il.com,
 kim.phillips@....com, lukas.bulwahn@...il.com, seanjc@...gle.com,
 jmattson@...gle.com, leitao@...ian.org, jpoimboe@...nel.org,
 rick.p.edgecombe@...el.com, kirill.shutemov@...ux.intel.com,
 jithu.joseph@...el.com, kai.huang@...el.com, kan.liang@...ux.intel.com,
 daniel.sneddon@...ux.intel.com, pbonzini@...hat.com, sandipan.das@....com,
 ilpo.jarvinen@...ux.intel.com, peternewman@...gle.com,
 maciej.wieczor-retman@...el.com, linux-doc@...r.kernel.org,
 linux-kernel@...r.kernel.org, eranian@...gle.com
Subject: Re: [PATCH v2 00/17] x86/resctrl : Support AMD Assignable Bandwidth
 Monitoring Counters (ABMC)

Hi Reinette,

On 2/23/24 11:17, Reinette Chatre wrote:
> 
> 
> On 2/20/2024 12:48 PM, Moger, Babu wrote:
>> On 2/20/24 09:21, James Morse wrote:
>>> On 19/01/2024 18:22, Babu Moger wrote:
> 
>>>> e. Enable ABMC mode.
>>>>
>>>> 	#echo 1 > /sys/fs/resctrl/info/L3_MON/mbm_assign_enable
>>>>         #cat /sys/fs/resctrl/info/L3_MON/mbm_assign_enable
>>>>         1
>>>
>>> Why does this mode need enabling? Can't it be enabled automatically on hardware that
>>> supports it, or enabled implicitly when the first assignment attempt arrives?
>>>
>>> I guess this is really needed for a reset - could we implement that instead? This way
>>> there isn't an extra step user-space has to do to make the assignments work.
>>
>> Mostly the new features are added as an opt-in method. So, kept it that
>> way. If we enable this feature automatically, then we have provide an
>> option to disable it.
>>
> 
> At the same time it sounds to me like ABMC can improve current users'
> experience without requiring them to do anything. This sounds appealing.
> For example, if I understand correctly, it may be possible to start resctrl
> with ABMC enabled by default and the number of monitoring groups (currently
> exposed to user space via "num_rmids") limited to the number of counters
> supported by ABMC. Existing users would then by default obtain better behavior
> of counters not resetting.

Yes, I like the idea. But i will break compatibility with pqos
tool(intel_cmt_cat utility). pqos tool monitoring will not work without
supporting ABMC enablement in the tool. ABMC feature requires an extra
step to assign the counters for monitor to work.

> 
> The "new feature" could then be viewed as adding support for more monitoring
> groups than what hardware can support concurrently.
> 
> Reinette

-- 
Thanks
Babu Moger