linux-kernel - Re: [PATCH] x86/intel_rdt: reinitialize cbm for new group allocation

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Date:   Mon, 9 Jan 2017 14:24:36 -0800
From:   Shaohua Li <shli@...com>
To:     Thomas Gleixner <tglx@...utronix.de>
CC:     Fenghua Yu <fenghua.yu@...el.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH] x86/intel_rdt: reinitialize cbm for new group allocation

On Mon, Jan 09, 2017 at 11:03:59PM +0100, Thomas Gleixner wrote:
> On Mon, 9 Jan 2017, Fenghua Yu wrote:
> > On Fri, Jan 06, 2017 at 04:05:19PM -0800, Shaohua Li wrote:
> > But since you come here now,  I would think reseting the CBM in
> > closid_free() is better.
> 
> No. closid_free() is the wrong place. closid_alloc/free() merily deal with
> the bitmap and nothing else.
> 
> If you really want to do that, then this needs a seperate function called
> from rmdir.
> 
> > The reason is user can see "right" max_cbm even through rdmsr after
> > rmdir, ie no gap for cbm values between rmdir and the next mkdir.
> 
> And the value pf this is?
> 
> The closid is not usable after the rmdir, so it's really completely
> uninteresting when the user can read the old value from that configuration
> MSR.
> 
> When the closid is reused then it hardly matters either what's in those cbm
> values (the old or max_cbm).

It's just a bit confusing. Ok, I'm fine with current behavior. Probably
document it somewhere in case others found the same issue.

Thanks,
Shaohua