linux-kernel - Re: [PATCH 4/5] x86/intel_rdt: Reset the cbm MSR during rmdir

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Date:   Wed, 1 Mar 2017 15:11:20 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Vikas Shivappa <vikas.shivappa@...ux.intel.com>
cc:     vikas.shivappa@...el.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 4/5] x86/intel_rdt: Reset the cbm MSR during rmdir

On Fri, 17 Feb 2017, Vikas Shivappa wrote:

> During rmdir reset the ctrl values to all 1s in the QOS_MSR for the
> directory's closid. This is done so that that next time when the closid
> is reused they dont reflect old values.

Sigh.

> +static int reset_all_ctrls(struct rdt_resource *r, u32 sclosid, u32 eclosid)

What's so wrong with using 'start' and 'end' instead of these cryptic names? 

>  {
>  	struct msr_param msr_param;
>  	cpumask_var_t cpu_mask;
> @@ -791,8 +791,8 @@ static int reset_all_cbms(struct rdt_resource *r)
>  		return -ENOMEM;
>  
>  	msr_param.res = r;
> -	msr_param.low = 0;
> -	msr_param.high = r->num_closid;
> +	msr_param.low = sclosid;
> +	msr_param.high = eclosid;
>  
>  	/*
>  	 * Disable resource control for this resource by setting all
> @@ -802,7 +802,7 @@ static int reset_all_cbms(struct rdt_resource *r)
>  	list_for_each_entry(d, &r->domains, list) {
>  		cpumask_set_cpu(cpumask_any(&d->cpu_mask), cpu_mask);
>  
> -		for (i = 0; i < r->num_closid; i++)
> +		for (i = sclosid; i < eclosid; i++)

'eclosid' or even when named 'end' is an outright bogus argument to this
function. What you really want is:

static int reset_all_ctrls(struct rdt_resource *r, u32 closid, u32 count)

which works here:

>  	for_each_enabled_rdt_resource(r)
> -		reset_all_cbms(r);
> +		reset_all_ctrls(r, 0, r->num_closid);

and makes this part understandable:

> +	/*
> +	 * Put domain control values back to default for the
> +	 * rdtgrp thats being removed.
> +	 */
> +	for_each_enabled_rdt_resource(r)
> +		reset_all_ctrls(r, rdtgrp->closid, rdtgrp->closid + 1);

		reset_all_ctrls(r, rdtgrp->closid, 1);

What you have done: 

> +		reset_all_ctrls(r, rdtgrp->closid, rdtgrp->closid + 1);

made me really look twice to figure out what the heck this is about.

Thanks,

	tglx