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

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Message-ID: <CALPaoChcJq5zoPchB2j0aM+nZpQe1xoo7w2QQUjtH+c58Yyxag@mail.gmail.com>
Date: Thu, 7 Mar 2024 15:14:25 -0800
From: Peter Newman <peternewman@...gle.com>
To: Reinette Chatre <reinette.chatre@...el.com>
Cc: babu.moger@....com, James Morse <james.morse@....com>, corbet@....net, 
	fenghua.yu@...el.com, tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, 
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	paulmck@...nel.org, rdunlap@...radead.org, tj@...nel.org, 
	peterz@...radead.org, yanjiewtw@...il.com, kim.phillips@....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 Reinette,

On Thu, Mar 7, 2024 at 2:53 PM Reinette Chatre
<reinette.chatre@...el.com> 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:
> >> 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'

The echo command uses buffered output through printf() and
putchar()[1]. The behavior of the buffering seems to be a write() call
after each newline, causing the kernel to see the request below as 32
individual commands.

>
> >
> > 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"?
> 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?

Yes, that would be helpful. The AMD implementations we use typically
have 16 domains or more.

Thanks!
-Peter

[1] https://git.savannah.gnu.org/cgit/bash.git/tree/builtins/echo.def