linux-kernel - Re: [PATCH V3 1/1] x86/resctrl: Remove unappropriate references to cacheinfo in the resctrl subsystem.

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Message-ID: <66d209ae-a41e-42b7-ba3d-2c3a4a9abfda@intel.com>
Date: Fri, 30 May 2025 10:29:41 -0700
From: Reinette Chatre <reinette.chatre@...el.com>
To: Qinyun Tan <qinyuntan@...ux.alibaba.com>, Tony Luck <tony.luck@...el.com>
CC: "H . Peter Anvin" <hpa@...or.com>, <linux-kernel@...r.kernel.org>,
	<x86@...nel.org>
Subject: Re: [PATCH V3 1/1] x86/resctrl: Remove unappropriate references to
 cacheinfo in the resctrl subsystem.

Hi Qinyun Tan,

On 5/29/25 7:12 PM, Qinyun Tan wrote:
> In the resctrl subsystem's Sub-NUMA Cluster (SNC) mode, the rdt_mon_domain
> structure representing a NUMA node relies on the cacheinfo interface
> (rdt_mon_domain::ci) to store L3 cache information (e.g., shared_cpu_map)
> for monitoring. The L3 cache information of a SNC NUMA node determines
> which domains are summed for the "top level" L3-scoped events.
> 
> rdt_mon_domain::ci is initialized using the first online CPU
> of a NUMA node. When this CPU goes offline, its shared_cpu_map is cleared
> to contain only the offline CPU itself.    Subsequently, attempting to read

nit: note extra spaces before "Subsequently"

> counters via smp_call_on_cpu(offline_cpu) fails (and error ignored),
> returning zero values for "top-level events" without any error indication.

nit: needs empty line here to separate the problem description and fix description into
separate paragraphs.

>   Replace the cacheinfo references in struct rdt_mon_domain and struct
> rmid_read with the cacheinfo ID (a unique identifier for the L3 cache).
> 
> rdt_domain_hdr::cpu_mask contains the online CPUs associated with that
> domain. When reading "top-level events", select a CPU from
> rdt_domain_hdr::cpu_mask and utilize its L3 shared_cpu_map to determine
> valid CPUs for reading RMID counter via the MSR interface.
> Considering all CPUs associated with the L3 cache improves the chances
> of picking a housekeeping CPU on which the counter reading work can be
> queued, avoiding an unnecessary IPI.
> 
> Fixes: 328ea68874642 ("x86/resctrl: Prepare for new Sub-NUMA Cluster (SNC) monitor files")
> Signed-off-by: Qinyun Tan <qinyuntan@...ux.alibaba.com>
> ---

The patch self did not change since v2 so Tony's "Tested-by" tag obtained
in [1] remains valid.

With spacing in changelog fixed you can also add:
| Reviewed-by: Reinette Chatre <reinette.chatre@...el.com>

Reinette

[1] https://lore.kernel.org/lkml/SJ1PR11MB6083BEDD3F7625B52E677647FC66A@SJ1PR11MB6083.namprd11.prod.outlook.com/