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 13:20:33 -0700
From:   "Luck, Tony" <tony.luck@...el.com>
To:     "Yu, Fenghua" <fenghua.yu@...el.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        "Anvin, H Peter" <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>,
        "Hansen, Dave" <dave.hansen@...el.com>,
        Nilay Vaish <nilayvaish@...il.com>, Shaohua Li <shli@...com>,
        David Carrillo-Cisneros <davidcc@...gle.com>,
        "Shankar, Ravi V" <ravi.v.shankar@...el.com>,
        "Prakhya, Sai Praneeth" <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

On Mon, Oct 17, 2016 at 09:43:41AM -0700, Yu, Fenghua wrote:
> > > > 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.
> 
> Right.
> 
> Also changing to uniform format <resname>:<id1>=cbm1;<id2>=cbm2;...
> is lot easier to parse schemata line in CDP mode.
> 
> So I'll change the code and doc to have two new resources: L3Data and L3Code for CDP mode.

Doc change (fold into part 05):
diff --git a/Documentation/x86/intel_rdt_ui.txt b/Documentation/x86/intel_rdt_ui.txt
index e56781952f42..b9f634c9a058 100644
--- a/Documentation/x86/intel_rdt_ui.txt
+++ b/Documentation/x86/intel_rdt_ui.txt
@@ -97,13 +97,18 @@ With CDP disabled the L3 schemata format is:
 
 L3 details (CDP enabled via mount option to resctrl)
 ----------------------------------------------------
-When CDP is enabled, you need to specify separate cache bit masks for
-code and data access. The generic format is:
+When CDP is enabled L3 control is split into two separate resources
+so you can specify independent masks for code and data like this:
 
-	L3:<cache_id0>=<d_cbm>,<i_cbm>;<cache_id1>=<d_cbm>,<i_cbm>;...
+	L3data:<cache_id0>=<cbm>;<cache_id1>=<cbm>;...
+	L3code:<cache_id0>=<cbm>;<cache_id1>=<cbm>;...
 
-where the d_cbm masks are for data access, and the i_cbm masks for code.
+L2 details
+----------
+L2 cache does not support code and data prioritization, so the
+schemata format is always:
 
+	L2:<cache_id0>=<cbm>;<cache_id1>=<cbm>;...
 
 Example 1
 ---------