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

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Message-ID: <46065d68-8334-4b76-bc68-c2695e7b98de@amd.com>
Date: Thu, 7 Mar 2024 21:50:21 -0600
From: "Moger, Babu" <babu.moger@....com>
To: Reinette Chatre <reinette.chatre@...el.com>,
 Peter Newman <peternewman@...gle.com>
Cc: 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, 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
Subject: Re: [PATCH v2 00/17] x86/resctrl : Support AMD Assignable Bandwidth
 Monitoring Counters (ABMC)

Hi Reinette/Peter,


On 3/7/24 16:53, Reinette Chatre wrote:
> Hi Peter,
> 
> On 3/7/2024 2:33 PM, Peter Newman wrote:
>> Hi Reinette,
>>
>> On Thu, Mar 7, 2024 at 12:41 PM Reinette Chatre
>> <reinette.chatre@...el.com> wrote:
>>>
>>> Hi Peter,
>>>
>>> On 3/7/2024 10:57 AM, Peter Newman wrote:
>>>> 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 intent of this interface is to support modification of several
>>> groups with a single write. These examples only show impact to a single
>>> group at a time, but multiple groups can be modified by separating
>>> configurations with a "\n". I believe Babu was planning to add some
>>> of these examples in his next iteration since it is not obvious yet.
>>>
>>>>
>>>> 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.
>>>
>>> I understood the proposed interface appeared to focus on one use case
>>> while the goal is to find an interface to support all requirements.
>>> With this proposed interface it it possible to make large scale changes
>>> with a single sysfs write.
>>
>> Ok I see you requested[1] one such example earlier.
>>
>> From what I've read, is this what you had in mind of reassigning 32
>> counters from the first 16 groups to the next?
>>
>> I had found that it's hard to get a single write() syscall out of a
>> string containing newlines, so I'm using one explicit call:
> 
> Apologies but this is not clear to me, could you please elaborate?
> 
> If you are referring to testing via shell you can try ANSI-C Quoting like:
> 	echo -n $'c1/m1/00=_\nc2/m2/00=_\n'
> 
>>
>> write([mbm_assign_control fd],
>> "/c1/m1/00=_;02=_;03=_;04=_;05=_;06=_;07=_;08=_;09=_;10=_;11=_;12=_;13=_;14=_;15=_\n"
>> "/c1/m2/00=_;01=_;02=_;03=_;04=_;05=_;06=_;07=_;08=_;09=_;10=_;11=_;12=_;13=_;14=_;15=_\n"
>> "/c1/m3/00=_;01=_;02=_;03=_;04=_;05=_;06=_;07=_;08=_;09=_;10=_;11=_;12=_;13=_;14=_;15=_\n"
>> [...]
>> "/c1/m14/00=_;01=_;02=_;03=_;04=_;05=_;06=_;07=_;08=_;09=_;10=_;11=_;12=_;13=_;14=_;15=_\n"
>> "/c1/m15/00=_;01=_;02=_;03=_;04=_;05=_;06=_;07=_;08=_;09=_;10=_;11=_;12=_;13=_;14=_;15=_\n"
>> "/c1/m16/00=lt;01=lt;02=lt;03=lt;04=lt;05=lt;06=lt;07=lt;08=lt;09=lt;10=lt;11=lt;12=lt;13=lt;14=lt;15=lt\n"
>> "/c1/m17/00=lt;01=lt;02=lt;03=lt;04=lt;05=lt;06=lt;07=lt;08=lt;09=lt;10=lt;11=lt;12=lt;13=lt;14=lt;15=lt\n"
>> "/c1/m18/00=lt;01=lt;02=lt;03=lt;04=lt;05=lt;06=lt;07=lt;08=lt;09=lt;10=lt;11=lt;12=lt;13=lt;14=lt;15=lt\n"
>> [...]
>> "/c1/m30/00=lt;01=lt;02=lt;03=lt;04=lt;05=lt;06=lt;07=lt;08=lt;09=lt;10=lt;11=lt;12=lt;13=lt;14=lt;15=lt\n"
>> "/c1/m31/00=lt;01=lt;02=lt;03=lt;04=lt;05=lt;06=lt;07=lt;08=lt;09=lt;10=lt;11=lt;12=lt;13=lt;14=lt;15=lt\n",
>> size);
> 
> (so far no "/" needed as prefix)
> 
> We could also consider some syntax to mean "all domains". For example,
> if no domain given then it can mean "all domains"?

Yea. Sound good to me. Will let you know if there are any troubles when I
start working on it.

I am also thinking about replacing the newline requirement for multiple
groups. Domains separate by "," and groups separate by ";".

Something like this..

"/c1/m1/00=_,01=_;/c1/m2/00=_,01=_;/c1/m3/00=lt,01=lt"

Thoughts?

> So, your example could possibly also be accomplished with a
> 
> 	c1/m1/=_\nc1/m2/=_\nc1/m3/=_\n [...] c1/m16/=lt\nc1/m17/=lt\nc1/m18/=_\n [...]
> 
> Any thoughts?
> 
> Reinette

-- 
Thanks
Babu Moger