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Message-ID: <3fe3f235-d8a6-453b-b69d-6b7f81c07ae1@amd.com>
Date: Fri, 23 Feb 2024 14:11:15 -0600
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Reply-To: babu.moger@amd.com
Subject: Re: [PATCH v2 00/17] x86/resctrl : Support AMD Assignable Bandwidth
 Monitoring Counters (ABMC)
Content-Language: en-US
To: Reinette Chatre <reinette.chatre@intel.com>,
 James Morse <james.morse@arm.com>, corbet@lwn.net, fenghua.yu@intel.com,
 tglx@linutronix.de, mingo@redhat.com, bp@alien8.de,
 dave.hansen@linux.intel.com
Cc: x86@kernel.org, hpa@zytor.com, paulmck@kernel.org, rdunlap@infradead.org,
 tj@kernel.org, peterz@infradead.org, yanjiewtw@gmail.com,
 kim.phillips@amd.com, lukas.bulwahn@gmail.com, seanjc@google.com,
 jmattson@google.com, leitao@debian.org, jpoimboe@kernel.org,
 rick.p.edgecombe@intel.com, kirill.shutemov@linux.intel.com,
 jithu.joseph@intel.com, kai.huang@intel.com, kan.liang@linux.intel.com,
 daniel.sneddon@linux.intel.com, pbonzini@redhat.com, sandipan.das@amd.com,
 ilpo.jarvinen@linux.intel.com, peternewman@google.com,
 maciej.wieczor-retman@intel.com, linux-doc@vger.kernel.org,
 linux-kernel@vger.kernel.org, eranian@google.com
References: <20231201005720.235639-1-babu.moger@amd.com>
 <cover.1705688538.git.babu.moger@amd.com>
 <2f373abf-f0c0-4f5d-9e22-1039a40a57f0@arm.com>
 <474ebe02-2d24-4ce3-b26a-46c520efd453@amd.com>
 <b6bb6a59-67c2-47bc-b8d3-04cf8fd21219@intel.com>
From: "Moger, Babu" <babu.moger@amd.com>
In-Reply-To: <b6bb6a59-67c2-47bc-b8d3-04cf8fd21219@intel.com>
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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