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Message-ID: <546228e7-0a77-42d3-b2a3-ed6b507f018e@intel.com>
Date: Thu, 30 May 2024 13:21:59 -0700
User-Agent: Mozilla Thunderbird
Subject: Re: [PATCH v19 11/20] x86/resctrl: Allocate a new bit in union
 mon_data_bits
To: Tony Luck <tony.luck@intel.com>, Fenghua Yu <fenghua.yu@intel.com>,
	"Maciej Wieczor-Retman" <maciej.wieczor-retman@intel.com>, Peter Newman
	<peternewman@google.com>, James Morse <james.morse@arm.com>, Babu Moger
	<babu.moger@amd.com>, Drew Fustini <dfustini@baylibre.com>, Dave Martin
	<Dave.Martin@arm.com>
CC: <x86@kernel.org>, <linux-kernel@vger.kernel.org>,
	<patches@lists.linux.dev>
References: <20240528222006.58283-1-tony.luck@intel.com>
 <20240528222006.58283-12-tony.luck@intel.com>
Content-Language: en-US
From: Reinette Chatre <reinette.chatre@intel.com>
In-Reply-To: <20240528222006.58283-12-tony.luck@intel.com>
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Hi Tony,

Regarding shortlog: isn't the purpose of this change to _avoid_
allocating a new bit?

On 5/28/24 3:19 PM, Tony Luck wrote:
> When Sub-NUMA Cluster (SNC) mode is enabled the legacy monitor reporting
> files must report the sum of the data from all of the SNC nodes that
> share the L3 cache that is referenced by the monitor file.
> 
> Resctrl squeezes all the attributes of these files into 32-bits so they
> can be stored in the "priv" field of struct kernfs_node.
> 
> Arbitrarily choose the "evtid" field to sacrifice one bit to make
> space for a new bit. This structure is purely internal to resctrl,

Missing explanation why this is ok for this field to sacrifice a bit.

> no ABI issues with modifying it. Subsequent changes may rearrange the
> allocation of bits between each of the fields as needed.
> 
> The stolen bit is given to a new "sum" field that indicates that reading

stolen? Is that necessary? It can just be "Give the bit ..." (also
note imperative tone)

> this file must sum across SNC nodes. This bit also indicates that the
> domid field is the l3_cache_id (instead of a domain id) to find which
> domains must be summed.

l3_cache_id looks like a variable that does not exist anywhere in this series
or in existing resctrl.

Reinette