linux-kernel - Re: [PATCH 2/5] x86/intel_rdt: Improvements to parsing schemata

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Date:   Sat, 11 Mar 2017 08:47:37 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     "Luck, Tony" <tony.luck@...el.com>
cc:     Shivappa Vikas <vikas.shivappa@...el.com>,
        Shivappa Vikas <vikas.shivappa@...ux.intel.com>,
        linux-kernel@...r.kernel.org, x86@...nel.org, hpa@...or.com,
        mingo@...nel.org, peterz@...radead.org, ravi.v.shankar@...el.com,
        fenghua.yu@...el.com, andi.kleen@...el.com
Subject: Re: [PATCH 2/5] x86/intel_rdt: Improvements to parsing schemata

On Fri, 10 Mar 2017, Luck, Tony wrote:
> On Fri, Mar 10, 2017 at 07:58:51PM +0100, Thomas Gleixner wrote:
> > Well, we have several options to tackle this:
> > 
> > 1) Have schemata files for each resource
> > 
> >    schemata_l2, _l3 _mb
> > 
> > 2) Request a full overwrite every time (all entries required)
> > 
> >    That still does not require ordering
> > 
> > 3) Allow full overwrite and 'append' mode
> > 
> >    echo "...." > schemata
> > 
> >    Overwrites the whole file. It does not require all entries to be
> >    supplied.  Non supplied entries are reset to default
> > 
> >    echo "...." >> schemata
> > 		 
> >    "Appends" the supplied entries by overwriting the existing ones.
> > 
> > My favourite would be #1, but I have no strong opinions other than not
> > caring about resource write ordering for #2 and #3.
> 
> If you are going to head in the direction of partial update, then
> why not go for:
> 
> 4) Drop the code that check that the user wrote all
>    the fields as well as the check for all the lines. Just update
>    the bits they list, and leave the rest unchanged.
> 
> I.e. the user could say:
> 
> # echo "L3:1=0x3f" > schemata
> 
> if they just wanted to update resource L3, instance 1.

Even better

> I don't think there is much benefit to the overwrite vs. append
> semantics for the user.

Agreed.

Thanks,

	tglx