linux-kernel - RE: [PATCH v4 13/18] x86/intel_rdt: Add mkdir to resctrl file system

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Message-ID: <alpine.DEB.2.20.1610180059380.6407@nanos>
Date:   Tue, 18 Oct 2016 01:03:09 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     "Luck, Tony" <tony.luck@...el.com>
cc:     "Yu, Fenghua" <fenghua.yu@...el.com>,
        "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 13/18] x86/intel_rdt: Add mkdir to resctrl file
 system

On Mon, 17 Oct 2016, Luck, Tony wrote:
> > So how are we going to deal with that in the schematas? Assume the L3=16
> > and L2=8 case(no CDP). So effectively any write of L2 to CLOSID=0 will
> > affect the setting of L2 in CLOSID=8.
> >
> > Will the code tell the user that L2 cannot be set for CLOSID >= 8? 
> >
> > Will it print the setting of CLOSID - 8 for CLOSID >= 8 when you read the
> > schemata file of CLOSID >= 8?
> 
> The default and first 7 directories you make will have lines in schemata for
> both L3 and L2.  The next 8 will just have L3 (and won't let you add L2).
> 
> > And of course this becomes very interesting when CLOSID 1 is deleted, then
> > what happens to CLOSID 9? Not to talk about the case when CLOSID 1 is
> > reused again.
> 
> Deleting CLOSID 1 won't affect CLOSID 9.

How so? CLOSID 9 is using CLOSID 1 L2 settings. Are we just keeping the L2
setting of CLOSID 1 around and do not reset it to default?

>  When you make a new directory that gets allocated CLOSID 1, it will have
>  both L3 and L2 lines.

Now CLOSID 1 is reused and reset to all 1's per default and even if not
then the operator will set a new L2 value and therefor wreckaging CLOSID 9.

Thanks,

	tglx