linux-kernel - RE: [PATCH] Documentation/x86: Document resctrl bandwidth control units are MiB

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Date: Tue, 2 Apr 2024 15:43:44 +0000
From: "Luck, Tony" <tony.luck@...el.com>
To: "Chatre, Reinette" <reinette.chatre@...el.com>
CC: "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>, "Yu, Fenghua"
	<fenghua.yu@...el.com>, Peter Newman <peternewman@...gle.com>, James Morse
	<james.morse@....com>, Babu Moger <babu.moger@....com>, Drew Fustini
	<dfustini@...libre.com>, "x86@...nel.org" <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"patches@...ts.linux.dev" <patches@...ts.linux.dev>
Subject: RE: [PATCH] Documentation/x86: Document resctrl bandwidth control
 units are MiB

> Changing the documentation does seem like the least controversial approach.
> The consequence is that resctrl documentation itself now switches back and
> forth between the units ... it uses MiBps for the software controller and
> GBps when referring to AMD and talking about memory bandwidth in general
> (see section Memory bandwidth Allocation and monitoring). I hope that it
> is clear enough that MiBps is just related to the software
> controller.

Babu,

In this section that Reinette refers to above:

  Reading/writing the schemata file (on AMD systems)
  --------------------------------------------------
  Reading the schemata file will show the current bandwidth limit on all
  domains. The allocated resources are in multiples of one eighth GB/s.
  When writing to the file, you need to specify what cache id you wish to
  configure the bandwidth limit. Reading the schemata file will show the current bandwidth limit on all
  domains. The allocated resources are in multiples of one eighth GB/s.
  When writing to the file, you need to specify what cache id you wish to
  configure the bandwidth limit.

Does "one eighth GB/s" mean 134217728 bytes/s or 125000000 bytes/s?

I.e. is the documentation accurate, or sloppily using GB/s when it should
have said GiB/s?

Thanks

-Tony