linux-kernel - Re: [PATCH v11 00/23] x86/resctrl : Support AMD Assignable Bandwidth Monitoring Counters (ABMC)

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Message-ID: <CALPaoCh7WpohzpXhSAbumjSZBv1_+1bXON7_V1pwG4bdEBr52Q@mail.gmail.com>
Date: Mon, 17 Feb 2025 11:26:50 +0100
From: Peter Newman <peternewman@...gle.com>
To: Reinette Chatre <reinette.chatre@...el.com>
Cc: "Moger, Babu" <bmoger@....com>, Dave Martin <Dave.Martin@....com>, Babu Moger <babu.moger@....com>, 
	corbet@....net, tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, 
	dave.hansen@...ux.intel.com, tony.luck@...el.com, x86@...nel.org, 
	hpa@...or.com, paulmck@...nel.org, akpm@...ux-foundation.org, 
	thuth@...hat.com, rostedt@...dmis.org, xiongwei.song@...driver.com, 
	pawan.kumar.gupta@...ux.intel.com, daniel.sneddon@...ux.intel.com, 
	jpoimboe@...nel.org, perry.yuan@....com, sandipan.das@....com, 
	kai.huang@...el.com, xiaoyao.li@...el.com, seanjc@...gle.com, 
	xin3.li@...el.com, andrew.cooper3@...rix.com, ebiggers@...gle.com, 
	mario.limonciello@....com, james.morse@....com, tan.shaopeng@...itsu.com, 
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org, 
	maciej.wieczor-retman@...el.com, eranian@...gle.com
Subject: Re: [PATCH v11 00/23] x86/resctrl : Support AMD Assignable Bandwidth
 Monitoring Counters (ABMC)

Hi Reinette,

On Fri, Feb 14, 2025 at 8:18 PM Reinette Chatre
<reinette.chatre@...el.com> wrote:
>
> Hi Babu,
>
> On 2/14/25 10:31 AM, Moger, Babu wrote:
> > On 2/14/2025 12:26 AM, Reinette Chatre wrote:
> >> On 2/13/25 9:37 AM, Dave Martin wrote:
> >>> On Wed, Feb 12, 2025 at 03:33:31PM -0800, Reinette Chatre wrote:
> >>>> On 2/12/25 9:46 AM, Dave Martin wrote:
> >>>>> On Wed, Jan 22, 2025 at 02:20:08PM -0600, Babu Moger wrote:
>
> (quoting relevant parts with goal to focus discussion on new possible syntax)
>
> >>>> I see the support for MPAM events distinct from the support of assignable counters.
> >>>> Once the MPAM events are sorted, I think that they can be assigned with existing interface.
> >>>> Please help me understand if you see it differently.
> >>>>
> >>>> Doing so would need to come up with alphabetical letters for these events,
> >>>> which seems to be needed for your proposal also? If we use possible flags of:
> >>>>
> >>>> mbm_local_read_bytes a
> >>>> mbm_local_write_bytes b
> >>>>
> >>>> Then mbm_assign_control can be used as:
> >>>> # echo '//0=ab;1=b' >/sys/fs/resctrl/info/L3_MON/mbm_assign_control
> >>>> # cat /sys/fs/resctrl/mon_data/mon_L3_00/mbm_local_read_bytes
> >>>> <value>
> >>>> # cat /sys/fs/resctrl/mon_data/mon_L3_00/mbm_local_bytes
> >>>> <sum of mbm_local_read_bytes and mbm_local_write_bytes>
> >>>>
> >>>> One issue would be when resctrl needs to support more than 26 events (no more flags available),
> >>>> assuming that upper case would be used for "shared" counters (unless this interface is defined
> >>>> differently and only few uppercase letters used for it). Would this be too low of a limit?
>
> As mentioned above, one possible issue with existing interface is that
> it is limited to 26 events (assuming only lower case letters are used). The limit
> is low enough to be of concern.

The events which can be monitored by a single counter on ABMC and MPAM
so far are combinable, so 26 counters per group today means it limits
breaking down MBM traffic for each group 26 ways. If a user complained
that a 26-way breakdown of a group's MBM traffic was limiting their
investigation, I would question whether they know what they're looking
for.

-Peter