linux-kernel - Re: [PATCH v6 14/30] x86,fs/resctrl: Support binary fixed point event counters

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Message-ID: <e93f23fb-b38e-4f6d-a801-dca5cc182b1b@nvidia.com>
Date: Fri, 27 Jun 2025 14:49:57 -0700
From: Fenghua Yu <fenghuay@...dia.com>
To: Tony Luck <tony.luck@...el.com>,
 Reinette Chatre <reinette.chatre@...el.com>,
 Maciej Wieczor-Retman <maciej.wieczor-retman@...el.com>,
 Peter Newman <peternewman@...gle.com>, James Morse <james.morse@....com>,
 Babu Moger <babu.moger@....com>, Drew Fustini <dfustini@...libre.com>,
 Dave Martin <Dave.Martin@....com>,
 Anil Keshavamurthy <anil.s.keshavamurthy@...el.com>,
 Chen Yu <yu.c.chen@...el.com>
Cc: x86@...nel.org, linux-kernel@...r.kernel.org, patches@...ts.linux.dev
Subject: Re: [PATCH v6 14/30] x86,fs/resctrl: Support binary fixed point event
 counters

Hi, Tony,

On 6/26/25 09:49, Tony Luck wrote:
> Resctrl was written with the assumption that all monitor events can be
> displayed as unsigned decimal integers.
>
> Hardware architecture counters may provide some telemetry events with
> greater precision where the event is not a simple count, but is a
> measurement of some sort (e.g. Joules for energy consumed).
>
> Add a new argument to resctrl_enable_mon_event() for architecture code
> to inform the file system that the value for a counter is a fixed-point
> value with a specific number of binary places.  The file system will
> only allow architecture to use floating point format on events that it
> marked with mon_evt::is_floating_point.
>
> Fixed point values are displayed with values rounded to an appropriate
> number of decimal places for the precision of the number of binary places
> provided. In general one extra decimal place is added for every three
> additional binary places. There are some exceptions for low precision
> binary values where exact representation is possible:
>
>    1 binary place is 0.0 or 0.5.			=> 1 decimal place
>    2 binary places is 0.0. 0.25, 0.5, 0.75	=> 2 decimal places

nit. s/0.0./0.0,/

[SNIP]

Thanks.

-Fenghua