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

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Message-ID: <alpine.DEB.2.20.1703101952040.3723@nanos>
Date:   Fri, 10 Mar 2017 19:58:51 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Shivappa Vikas <vikas.shivappa@...el.com>
cc:     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,
        tony.luck@...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, Shivappa Vikas wrote:
> On Fri, 10 Mar 2017, Thomas Gleixner wrote:
> > It's fine to display them in a defined order, but there is no point to
> > enforce the ordering on write.
> > 
> > The real question here is whether we really have to write every line on
> > every update. IMO it's sufficient to write a single resource line and not
> > require to update all resources every time.
> 
> Ok in that case we can drop this. because my thought was that user wants to
> see the contents he wrote when he overwrites the whole file like below , IOW
> its wierd for user to do
> 
> # echo "L3:0=0xff;1=0xf0" > /sys/fs/resctrl/schemata
> then
> 
> # cat /sys/fs/resctrl/schemata
> L3:0=0xff;1=0xf0
> L2:0=0xff;1=0xf0
> MB:....
> 
> But he did not write the L2,MB when he did an overwrite of the whole file.

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.

Thanks,

	tglx