linux-kernel - Re: [PATCH v4 11/18] x86/intel_rdt: Add basic resctrl filesystem support

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Date:   Mon, 17 Oct 2016 21:35:34 +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 v4 11/18] x86/intel_rdt: Add basic resctrl filesystem
 support

On Fri, 14 Oct 2016, Fenghua Yu wrote:
> +++ b/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c
> + *
> + * More information about RDT be found in the Intel (R) x86 Architecture
> + * Software Developer Manual.

Yes, that's how it should look like.

> +static void l3_qos_cfg_update(void *arg)
> +{
> +	struct rdt_resource *r = arg;
> +
> +	wrmsrl(IA32_L3_QOS_CFG, r->cdp_enabled);
> +}
> +
> +static void set_l3_qos_cfg(struct rdt_resource *r)
> +{
> +	struct list_head *l;
> +	struct rdt_domain *d;
> +	struct cpumask cpu_mask;

You cannot have cpumasks on stack.

        cpumask_var_t mask;

        if (!zalloc_cpumask_var(&mask, GFP_KERNEL))
                return -ENOMEM;


> +	int cpu;
> +
> +	cpumask_clear(&cpu_mask);

That can go away then

> +	list_for_each(l, &r->domains) {

list_for_each_entry() again

> +		d = list_entry(l, struct rdt_domain, list);
> +		cpumask_set_cpu(cpumask_any(&d->cpu_mask), &cpu_mask);

A comment to explain what this does would be helpful.

> +	}
> +	cpu = get_cpu();
> +	/* Update QOS_CFG MSR on this cpu if it's in cpu_mask. */
> +	if (cpumask_test_cpu(cpu, &cpu_mask))
> +		l3_qos_cfg_update(r);
> +	/* Update QOS_CFG MSR on all other cpus in cpu_mask. */
> +	smp_call_function_many(&cpu_mask, l3_qos_cfg_update, r, 1);
> +	put_cpu();
> +}
> +
> +static int parse_rdtgroupfs_options(char *data)
> +{
> +	char *token, *o = data;
> +	struct rdt_resource *r = &rdt_resources_all[RDT_RESOURCE_L3];
> +
> +	r->cdp_enabled = false;
> +	while ((token = strsep(&o, ",")) != NULL) {
> +		if (!*token)
> +			return -EINVAL;
> +
> +		if (!strcmp(token, "cdp"))
> +			if (r->enabled && r->cdp_capable)
> +				r->cdp_enabled = true;
> +	}
> +
> +	return 0;
> +}
> +
> +static struct dentry *rdt_mount(struct file_system_type *fs_type,
> +				int flags, const char *unused_dev_name,
> +				void *data)
> +{
> +	struct dentry *dentry;
> +	int ret;
> +	bool new_sb;
> +
> +	mutex_lock(&rdtgroup_mutex);
> +	/*
> +	 * resctrl file system can only be mounted once.
> +	 */
> +	if (static_branch_unlikely(&rdt_enable_key)) {
> +		dentry = ERR_PTR(-EBUSY);
> +		goto out;
> +	}
> +
> +	ret = parse_rdtgroupfs_options(data);
> +	if (ret) {
> +		dentry = ERR_PTR(ret);
> +		goto out;
> +	}
> +
> +	dentry = kernfs_mount(fs_type, flags, rdt_root,
> +			      RDTGROUP_SUPER_MAGIC, &new_sb);

&new_sb is pointless here. It just tells the caller that a new superblock
has been created, So in case of a valid dentry new_sb will always be true,
and if anything failed in kernfs_mount() including the allocation of a new
superblock then new_sb is completely irrelevant as IS_ERR(dentry) will be
true. So you can just hand in NULL because you do not allow multiple
mounts.

> +	if (IS_ERR(dentry))
> +		goto out;
> +	if (!new_sb) {
> +		dentry = ERR_PTR(-EINVAL);
> +		goto out;
> +	}
> +	if (rdt_resources_all[RDT_RESOURCE_L3].cdp_capable)
> +		set_l3_qos_cfg(&rdt_resources_all[RDT_RESOURCE_L3]);
> +	static_branch_enable(&rdt_enable_key);
> +
> +out:
> +	mutex_unlock(&rdtgroup_mutex);
> +
> +	return dentry;
> +}
> +
> +static void reset_all_cbms(struct rdt_resource *r)
> +{
> +	struct list_head *l;
> +	struct rdt_domain *d;
> +	struct msr_param msr_param;
> +	struct cpumask cpu_mask;
> +	int i, cpu;
> +
> +	cpumask_clear(&cpu_mask);
> +	msr_param.res = r;
> +	msr_param.low = 0;
> +	msr_param.high = r->max_closid;
> +
> +	list_for_each(l, &r->domains) {
> +		d = list_entry(l, struct rdt_domain, list);

list_for_each_entry()

> +		cpumask_set_cpu(cpumask_any(&d->cpu_mask), &cpu_mask);
> +
> +		for (i = 0; i < r->max_closid; i++)
> +			d->cbm[i] = r->max_cbm;
> +	}
> +	cpu = get_cpu();
> +	/* Update CBM on this cpu if it's in cpu_mask. */
> +	if (cpumask_test_cpu(cpu, &cpu_mask))
> +		rdt_cbm_update(&msr_param);
> +	/* Updte CBM on all other cpus in cpu_mask. */

Update

> +	smp_call_function_many(&cpu_mask, rdt_cbm_update, &msr_param, 1);
> +	put_cpu();
> +}
> +

Thanks,

	tglx