linux-kernel - Re: [PATCH v5 10/18] x86/intel_rdt: Build structures for each resource based on cache topology

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Date:   Wed, 26 Oct 2016 15:02:56 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Fenghua Yu <fenghua.yu@...el.com>
cc:     "H. Peter Anvin" <h.peter.anvin@...el.com>,
        Ingo Molnar <mingo@...e.hu>, Tony Luck <tony.luck@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Stephane Eranian <eranian@...gle.com>,
        Borislav Petkov <bp@...e.de>,
        Dave Hansen <dave.hansen@...el.com>,
        Nilay Vaish <nilayvaish@...il.com>, Shaohua Li <shli@...com>,
        David Carrillo-Cisneros <davidcc@...gle.com>,
        Ravi V Shankar <ravi.v.shankar@...el.com>,
        Sai Prakhya <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 v5 10/18] x86/intel_rdt: Build structures for each resource
 based on cache topology

On Sat, 22 Oct 2016, Fenghua Yu wrote:
> +void rdt_cbm_update(void *arg)
> +{
> +	struct msr_param *m = (struct msr_param *)arg;
> +	struct rdt_resource *r = m->res;
> +	int i, cpu = smp_processor_id();
> +	struct rdt_domain *d;
> +
> +	list_for_each_entry(d, &r->domains, list) {

> +static struct rdt_domain *rdt_find_domain(struct rdt_resource *r, int id,
> +					  struct list_head **pos)
> +{
> +	struct rdt_domain *d;
> +	struct list_head *l;
> +
> +	if (id < 0)
> +		return ERR_PTR(id);
> +
> +	list_for_each(l, &r->domains) {
> +		d = list_entry(l, struct rdt_domain, list);

So above you converted to list_for_each_entry(). Is there a sensible
reason, aside of being sloppy, why is this still using list_for_each()?

> +		/* When id is found, return its domain. */
> +		if (id == d->id)
> +			return d;
> +		/* Stop searching when finding id's position in sorted list. */

What is the reason that this needs to be in a sorted list?

I haven't found one so far. And if there is none, then this can use a hlist.

> +		if (id < d->id)
> +			break;
> +	}
> +	/*
> +	 * No id is found in resource domains. Record the position
> +	 * that the new domain will be added. The posistion is not used
> +	 * when removing a domain.

This comment makes no sense. If you want to document that a caller does not
require the @pos argument, then you really should make it optional and do

	if (pos)
		*pos = l;

But before doing that blindly, you want to explain why sorting is required
at all.

> +	 */
> +	*pos = l;
> +
> +	return NULL;
> +}
> +
> +static void domain_add_cpu(int cpu, struct rdt_resource *r)
> +{
> +	int i, id = get_cache_id(cpu, r->cache_level);
> +	struct list_head *add_pos = NULL;
> +	struct rdt_domain *d;
> +
> +	d = rdt_find_domain(r, id, &add_pos);
> +	if (IS_ERR(d)) {
> +		pr_warn("Could't find cache id for cpu %d\n", cpu);
> +		return;
> +	}
> +
> +	if (d) {
> +		cpumask_set_cpu(cpu, &d->cpu_mask);
> +		return;
> +	}
> +
> +	if (!add_pos) {
> +		pr_warn("Couldn't add cpu %d in %s domain\n", cpu, r->name);

Errm, how can add_pos ever be NULL if you get here? Not at all AFAICT.

> +		return;
> +	}
> +
> +	d = kzalloc_node(sizeof(*d), GFP_KERNEL, cpu_to_node(cpu));
> +	if (!d)
> +		return;
> +
> +	d->id = id;

Please move this after the allocation. This random code ordering just makes
reading hard as one expects that d->id is a prerequisite for the
allocation.

> +	d->cbm = kmalloc_array(r->num_closid, sizeof(*d->cbm), GFP_KERNEL);
> +	if (!d->cbm) {
> +		pr_warn("Failed to alloc CBM array for cpu %d\n", cpu);
> +		kfree(d);
> +		return;
> +	}

New line please. Visually seperating logical code blocks enhances
readability.

> +	for (i = 0; i < r->num_closid; i++) {

Thanks,

	tglx