linux-kernel - Re: [PATCH v4 08/18] x86/intel_rdt: Pick up L3/L2 RDT parameters from CPUID

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Date:   Mon, 17 Oct 2016 09:35:25 -0700
From:   "Luck, Tony" <tony.luck@...el.com>
To:     Fenghua Yu <fenghua.yu@...el.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <h.peter.anvin@...el.com>,
        Ingo Molnar <mingo@...e.hu>,
        Peter Zijlstra <peterz@...radead.org>,
        Stephane Eranian <eranian@...gle.com>,
        Borislav Petkov <bp@...e.de>,
        Dave Hansen <dave.hansen@...el.com>,
        Nilay Vaish <nilayvaish@...il.com>, Shaohua Li <shli@...com>,
        David Carrillo-Cisneros <davidcc@...gle.com>,
        Ravi V Shankar <ravi.v.shankar@...el.com>,
        Sai Prakhya <sai.praneeth.prakhya@...el.com>,
        Vikas Shivappa <vikas.shivappa@...ux.intel.com>,
        linux-kernel <linux-kernel@...r.kernel.org>, x86 <x86@...nel.org>
Subject: Re: [PATCH v4 08/18] x86/intel_rdt: Pick up L3/L2 RDT parameters
 from CPUID

> > I wonder whether this is the proper abstraction level. We might as well do
> > the following:
> > 
> > rdtresources[] = {
> >      {
> > 	.name	= "L3",
> >      },
> >      {
> > 	.name	= "L3Data",
> >      },
> >      {
> > 	.name	= "L3Code",
> >      },
> > 
> > and enable either L3 or L3Data+L3Code. Not sure if that makes things
> > simpler, but it's definitely worth a thought or two.
> 
> This way will be better than having cdp_enabled/capable for L3 and not
> for L2.  And this doesn't change current userinterface design either,
> I think.

User interface would change if you did this. The schemata file would
look like this with CDP enabled:

# cat schemata
L3Data:0=fffff;1=fffff;2=fffff;3=fffff
L3Code:0=fffff;1=fffff;2=fffff;3=fffff

but that is easier to read than the current:

# cat schemata
L3:0=fffff,fffff;1=fffff,fffff;2=fffff,fffff;3=fffff,fffff

which gives you no clue on which mask is code and which is data.

We'd also end up with "info/L3Data/" and "info/L3code/"
which would be a little redundant (since the files in each
would contain the same numbers), but perhaps that is worth
it to get the better schemata file.

-Tony