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

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Date:   Fri, 10 Mar 2017 14:05:51 -0800
From:   "Luck, Tony" <tony.luck@...el.com>
To:     Thomas Gleixner <tglx@...utronix.de>
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, 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.

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

-Tony