linux-kernel - Re: [PATCH v14 12/32] x86,fs/resctrl: Support binary fixed point event counters

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Message-ID: <19a6a5ec-9039-4735-a260-613cd63a9791@intel.com>
Date: Tue, 2 Dec 2025 08:11:21 -0800
From: Reinette Chatre <reinette.chatre@...el.com>
To: Tony Luck <tony.luck@...el.com>, Fenghua Yu <fenghuay@...dia.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>, Chen Yu <yu.c.chen@...el.com>
CC: <x86@...nel.org>, <linux-kernel@...r.kernel.org>,
	<patches@...ts.linux.dev>
Subject: Re: [PATCH v14 12/32] x86,fs/resctrl: Support binary fixed point
 event counters

Hi Tony,

On 11/24/25 10:53 AM, Tony Luck wrote:
> resctrl assumes 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 final paragraph of changelog seems to actually form part of above, and did so
in v13. This new split seems unnecessary and confusing to me.

> 
> Display fixed point values with values rounded to ceil(binary_bits * log10(2))
> decimal places. Special case for zero binary bits to print "{value}.0".
> 
> Only allow architecture to use floating point format on events that the file
> system has marked with mon_evt::is_floating_point.

Considering some questions surrounding this name this could append something like:
"... which reflects the contract with user space on how the event values are displayed."

> 
> Signed-off-by: Tony Luck <tony.luck@...el.com>
> Reviewed-by: Reinette Chatre <reinette.chatre@...el.com>
> ---

Reinette