linux-kernel - Re: [RFC PATCH v3 00/17] x86/resctrl : Support AMD Assignable Bandwidth Monitoring Counters (ABMC)

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Message-ID: <ZiffF93HM8bE3qo7@e133380.arm.com>
Date: Tue, 23 Apr 2024 17:17:27 +0100
From: Dave Martin <Dave.Martin@....com>
To: "Moger, Babu" <babu.moger@....com>
Cc: Peter Newman <peternewman@...gle.com>, corbet@....net,
	fenghua.yu@...el.com, reinette.chatre@...el.com, tglx@...utronix.de,
	mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com,
	x86@...nel.org, hpa@...or.com, paulmck@...nel.org,
	rdunlap@...radead.org, tj@...nel.org, peterz@...radead.org,
	yanjiewtw@...il.com, kim.phillips@....com, lukas.bulwahn@...il.com,
	seanjc@...gle.com, jmattson@...gle.com, leitao@...ian.org,
	jpoimboe@...nel.org, rick.p.edgecombe@...el.com,
	kirill.shutemov@...ux.intel.com, jithu.joseph@...el.com,
	kai.huang@...el.com, kan.liang@...ux.intel.com,
	daniel.sneddon@...ux.intel.com, pbonzini@...hat.com,
	sandipan.das@....com, ilpo.jarvinen@...ux.intel.com,
	maciej.wieczor-retman@...el.com, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org, eranian@...gle.com,
	james.morse@....com
Subject: Re: [RFC PATCH v3 00/17] x86/resctrl : Support AMD Assignable
 Bandwidth Monitoring Counters (ABMC)

Hi Babu,

On Tue, Apr 23, 2024 at 10:43:25AM -0500, Moger, Babu wrote:
> Hi Dave,
> 
> On 4/23/24 07:38, Dave Martin wrote:
> > Hi Peter,
> > 
> > On Mon, Apr 22, 2024 at 11:23:50AM -0700, Peter Newman wrote:
> >> Hi Dave,
> >>
> >> On Mon, Apr 22, 2024 at 9:33 AM Dave Martin <Dave.Martin@....com> wrote:
> >>>
> >>> Hi Babu,
> >>>
> >>> On Thu, Mar 28, 2024 at 08:06:33PM -0500, Babu Moger wrote:
> >>>>        Assignment flags can be one of the following:
> >>>>
> >>>>         t  MBM total event is assigned
> >>>
> >>> With my MPAM hat on this looks a bit weird, although I suppose it
> >>> follows on from the way "mbm_total_bytes" and "mbm_local_bytes" are
> >>> already exposed in resctrlfs.
> >>>
> >>> From an abstract point of view, "total" and "local" are just event
> >>> selection criteria, additional to those in mbm_cfg_mask.  The different
> >>> way they are treated in the hardware feels like an x86 implementation
> >>> detail.
> >>>
> >>> For MPAM we don't currently distinguish local from non-local traffic, so
> >>> I guess this just reduces to a simple on-off (i.e., "t" or nothing),
> >>> which I guess is tolerable.
> >>>
> >>> This might want more thought if there is an expectation that more
> >>> categories will be added here, though (?)
> >>
> >> There should be a path forward whenever we start supporting
> >> user-configured counter classes. I assume the letters a-z will be
> >> enough to cover all the counter classes which could be used at once.
> > 
> > Ack, though I'd appreciate a response on the point about "_" below in
> > case people missed it.
> 
> It was based on the dynamic debug interface and also Reinette's suggestion
> as well.
> https://www.kernel.org/doc/html/v4.10/admin-guide/dynamic-debug-howto.html
> (Look for "No flags are set").
> 
> We tried to use that similar interface.

Fair enough; I haven't touched dynamic debug for quite a while and had
forgotten about this convention being used there.

Apologies for the noise on that!

Cheers
---Dave