linux-kernel - Re: [PATCH v2 00/17] x86/resctrl : Support AMD Assignable Bandwidth Monitoring Counters (ABMC)

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Message-ID: <CALPaoCi=PCWr6U5zYtFPmyaFHU_iqZtZL-LaHC2mYxbETXk3ig@mail.gmail.com>
Date: Thu, 7 Mar 2024 10:57:45 -0800
From: Peter Newman <peternewman@...gle.com>
To: babu.moger@....com
Cc: Reinette Chatre <reinette.chatre@...el.com>, James Morse <james.morse@....com>, corbet@....net, 
	fenghua.yu@...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, 
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	maciej.wieczor-retman@...el.com, linux-doc@...r.kernel.org, 
	linux-kernel@...r.kernel.org, eranian@...gle.com
Subject: Re: [PATCH v2 00/17] x86/resctrl : Support AMD Assignable Bandwidth
 Monitoring Counters (ABMC)

Hi Babu,

On Mon, Mar 4, 2024 at 2:24 PM Moger, Babu <bmoger@....com> wrote:
> Based on our discussion, I am listing few examples here. Let me know if
> I missed something.
>
>    mount  -t resctrl resctrl /sys/fs/resctrl/
>
> 1. Assign both local and total counters to default group on domain 0 and 1.
>     $echo "//00=lt;01=lt" > /sys/fs/resctrl/info/L3_MON/mbm_assign_control
>
>     $cat /sys/fs/resctrl/info/L3_MON/mbm_assign_control
>     //00=lt;01=lt
>
> 2. Assign a total event to mon group inside the default group for both
> domain 0 and 1.
>
>     $mkdir /sys/fs/resctrl/mon_groups/mon_a
>     $echo "/mon_a/00+t;01+t" >
> /sys/fs/resctrl/info/L3_MON/mbm_assign_control
>
>     $cat /sys/fs/resctrl/info/L3_MON/mbm_assign_control
>     //00=lt;01=lt
>     /mon_a/00=t;01=t
>
> 3. Assign a local event to non-default control mon group both domain 0
> and 1.
>     $mkdir /sys/fs/resctrl/ctrl_a
>     $echo "/ctrl_a/00=l;01=l"  >
> /sys/fs/resctrl/info/L3_MON/mbm_assign_control
>
>     $cat /sys/fs/resctrl/info/L3_MON/mbm_assign_control
>     //00=lt;01=lt
>     /mon_a/00=t;01=t
>     /ctrl_a/00=l;01=l
>
> 4. Assign a both counters to mon group inside another control
> group(non-default).
>     $mkdir /sys/fs/resctrl/ctrl_a/mon_ab/
>     $echo "ctrl_a/mon_ab/00=lt;01=lt" >
> /sys/fs/resctrl/nfo/L3_MON/mbm_assign_contro
>
>     $cat /sys/fs/resctrl/info/L3_MON/mbm_assign_control
>     //00=lt;01=lt
>     /mon_a/00=t;01=t
>     /ctrl_a/00=l;01=l
>     ctrl_a/mon_ab/00=lt;01=lt
>
> 5. Unassign a counter to mon group inside another control
> group(non-default).
>     $echo "ctrl_a/mon_ab/00-l;01-l" >
> /sys/fs/resctrl/nfo/L3_MON/mbm_assign_control
>
>    $cat /sys/fs/resctrl/info/L3_MON/mbm_assign_control
>    //00=lt;01=lt
>    /mon_a/00=t;01=t
>    /ctrl_a/00=l;01=l
>    ctrl_a/mon_ab/00=t;01=t
>
> 6. Unassign all the counters on a specific group.
>     $echo "ctrl_a/mon_ab/00=_" >
> /sys/fs/resctrl/nfo/L3_MON/mbm_assign_control
>
>     $cat /sys/fs/resctrl/info/L3_MON/mbm_assign_control
>     //00=lt;01=lt
>     /mon_a/00=t;01=t
>     /ctrl_a/00=l;01=l
>     ctrl_a/mon_ab/00=_;01=_

The use case I'm interested in is iterating 32 counters over 256
groups[1]. If it's not possible to reassign 32 counters in a single
write system call, with just one IPI per domain per batch reassignment
operation, then I don't see any advantage over the original proposal
with the assignment control file in every group directory. We already
had fine-grained control placing assign/unassign nodes throughout the
directory hierarchy, with the scope implicit in the directory
location.

The interface I proposed in [1] aims to reduce the per-domain IPIs by
a factor of the number of counters, rather than sending off 2 rounds
of IPIs to each domain for each monitoring group.

-Peter

[1] https://lore.kernel.org/lkml/CALPaoChhKJiMAueFtgCTc7ffO++S5DJCySmxqf9ZDmhR9RQapw@mail.gmail.com/