linux-kernel - Re: [PATCH 13/21] x86/intel_rdt/cqm: Add cpus file support

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Date:   Sun, 2 Jul 2017 14:29:27 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Vikas Shivappa <vikas.shivappa@...ux.intel.com>
cc:     x86@...nel.org, linux-kernel@...r.kernel.org, hpa@...or.com,
        peterz@...radead.org, ravi.v.shankar@...el.com,
        vikas.shivappa@...el.com, tony.luck@...el.com,
        fenghua.yu@...el.com, andi.kleen@...el.com
Subject: Re: [PATCH 13/21] x86/intel_rdt/cqm: Add cpus file support

On Mon, 26 Jun 2017, Vikas Shivappa wrote:
> -static ssize_t rdtgroup_cpus_write(struct kernfs_open_file *of,
> -				   char *buf, size_t nbytes, loff_t off)
> +static ssize_t cpus_mon_write(struct kernfs_open_file *of,
> +			      char *buf, size_t nbytes,
> +			      struct rdtgroup *rdtgrp)

Again. Please make the split of rdtgroup_cpus_write() as a seperate
preparatory change first and just move the guts of the existing write
function out into cpus_ctrl_write() and then add the mon_write stuff as an
extra patch.

>  {
> +	struct rdtgroup *pr = rdtgrp->parent, *cr;

 *pr and *cr really suck. 

>  	cpumask_var_t tmpmask, newmask;
> -	struct rdtgroup *rdtgrp, *r;
> +	struct list_head *llist;
>  	int ret;
>  
> -	if (!buf)
> -		return -EINVAL;
> -
>  	if (!zalloc_cpumask_var(&tmpmask, GFP_KERNEL))
>  		return -ENOMEM;
>  	if (!zalloc_cpumask_var(&newmask, GFP_KERNEL)) {
> @@ -233,10 +235,89 @@ static ssize_t rdtgroup_cpus_write(struct kernfs_open_file *of,
>  		return -ENOMEM;
>  	}
>  
> -	rdtgrp = rdtgroup_kn_lock_live(of->kn);
> -	if (!rdtgrp) {
> -		ret = -ENOENT;
> -		goto unlock;
> +	if (is_cpu_list(of))
> +		ret = cpulist_parse(buf, newmask);
> +	else
> +		ret = cpumask_parse(buf, newmask);

The cpuask allocation and parsing of the user buffer can be done in the
common code. No point in duplicating that.

> +
> +	if (ret)
> +		goto out;
> +
> +	/* check that user didn't specify any offline cpus */
> +	cpumask_andnot(tmpmask, newmask, cpu_online_mask);
> +	if (cpumask_weight(tmpmask)) {
> +		ret = -EINVAL;
> +		goto out;
> +	}

Common code.

> +	/* Check whether cpus belong to parent ctrl group */
> +	cpumask_andnot(tmpmask, newmask, &pr->cpu_mask);
> +	if (cpumask_weight(tmpmask)) {
> +		ret = -EINVAL;
> +		goto out;
> +	}
> +
> +	/* Check whether cpus are dropped from this group */
> +	cpumask_andnot(tmpmask, &rdtgrp->cpu_mask, newmask);
> +	if (cpumask_weight(tmpmask)) {
> +		/* Give any dropped cpus to parent rdtgroup */
> +		cpumask_or(&pr->cpu_mask, &pr->cpu_mask, tmpmask);

This does not make any sense. The check above verifies that all cpus in
newmask belong to the parent->cpu_mask. If they don't then you return
-EINVAL, but here you give them back to parent->cpu_mask. How is that
supposed to work? You never get into this code path!

So you need a seperate mask in the parent rdtgroup to store the CPUs which
are valid in any monitoring group which belongs to it. So the logic
becomes:

	/*
	 * Check whether the CPU mask is a subset of the CPUs
	 * which belong to the parent group.
	 */
	cpumask_andnot(tmpmask, newmask, parent->cpus_valid_mask);
	if (cpumask_weight(tmpmask))
		return -EINVAL;

When CAT is not available, then parent->cpus_valid_mask is a pointer to
cpu_online_mask. When CAT is enabled, then parent->cpus_valid_mask is a
pointer to the CAT group cpu mask.

> +		update_closid_rmid(tmpmask, pr);
> +	}
> +
> +	/*
> +	 * If we added cpus, remove them from previous group that owned them
> +	 * and update per-cpu rmid
> +	 */
> +	cpumask_andnot(tmpmask, newmask, &rdtgrp->cpu_mask);
> +	if (cpumask_weight(tmpmask)) {
> +		llist = &pr->crdtgrp_list;

llist is a bad name. We have a facility llist, i.e. lockless list. head ?

> +		list_for_each_entry(cr, llist, crdtgrp_list) {
> +			if (cr == rdtgrp)
> +				continue;
> +			cpumask_andnot(&cr->cpu_mask, &cr->cpu_mask, tmpmask);
> +		}
> +		update_closid_rmid(tmpmask, rdtgrp);
> +	}

> +static void cpumask_rdtgrp_clear(struct rdtgroup *r, struct cpumask *m)
> +{
> +	struct rdtgroup *cr;
> +
> +	cpumask_andnot(&r->cpu_mask, &r->cpu_mask, m);
> +	/* update the child mon group masks as well*/
> +	list_for_each_entry(cr, &r->crdtgrp_list, crdtgrp_list)
> +		cpumask_and(&cr->cpu_mask, &r->cpu_mask, &cr->cpu_mask);

That's equally wrong. See above.

Thanks,

	tglx