Message-ID: <20190807152511.GB24328@zn.tnic>
Date:   Wed, 7 Aug 2019 17:25:11 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Reinette Chatre <reinette.chatre@...el.com>
Cc:     tglx@...utronix.de, fenghua.yu@...el.com, tony.luck@...el.com,
        kuo-lang.tseng@...el.com, mingo@...hat.com, hpa@...or.com,
        x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2 09/10] x86/resctrl: Pseudo-lock portions of multiple
 resources

On Tue, Jul 30, 2019 at 10:29:43AM -0700, Reinette Chatre wrote:
> A cache pseudo-locked region may span more than one level of cache. A
> part of the pseudo-locked region that falls on one cache level is
> referred to as a pseudo-lock portion that was introduced previously.
> 
> Now a pseudo-locked region is allowed to have two portions instead of
> the previous limit of one. When a pseudo-locked region consists out of
> two portions it can only span a L2 and L3 resctrl resource.
> When a pseudo-locked region consists out of a L2 and L3 portion then
> there are some requirements:
> - the L2 and L3 cache has to be in same cache hierarchy
> - the L3 portion must be same size or larger than L2 portion
> 
> As documented in previous changes the list of portions are
> maintained so that the L2 portion would always appear first in the list
> to simplify any information retrieval.
> 
> Signed-off-by: Reinette Chatre <reinette.chatre@...el.com>
> ---
>  arch/x86/kernel/cpu/resctrl/pseudo_lock.c | 142 +++++++++++++++++++++-
>  1 file changed, 139 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/resctrl/pseudo_lock.c b/arch/x86/kernel/cpu/resctrl/pseudo_lock.c
> index 717ea26e325b..7ab4e85a33a7 100644
> --- a/arch/x86/kernel/cpu/resctrl/pseudo_lock.c
> +++ b/arch/x86/kernel/cpu/resctrl/pseudo_lock.c
> @@ -339,13 +339,104 @@ static int pseudo_lock_single_portion_valid(struct pseudo_lock_region *plr,
>  	return -1;
>  }
>  
> +/**
> + * pseudo_lock_l2_l3_portions_valid - Verify region across L2 and L3
> + * @plr: Pseudo-Locked region
> + * @l2_portion: L2 Cache portion of pseudo-locked region
> + * @l3_portion: L3 Cache portion of pseudo-locked region
> + *
> + * User requested a pseudo-locked region consisting of a L2 as well as L3
> + * cache portion. The portions are tested as follows:
> + *   - L2 and L3 cache instances have to be in the same cache hierarchy.
> + *     This is tested by ensuring that the L2 portion's cpumask is a
> + *     subset of the L3 portion's cpumask.
> + *   - L3 portion must be same size or larger than L2 portion.
> + *
> + * Return: -1 if the portions are unable to be used for a pseudo-locked
> + *         region, 0 if the portions could be used for a pseudo-locked
> + *         region. When returning 0:
> + *         - the pseudo-locked region's size, line_size (cache line length)
> + *           and CPU on which locking thread will be run are set.
> + *         - CPUs associated with L2 cache portion are constrained from
> + *           entering C-state that will affect the pseudo-locked region.
> + */
> +static int pseudo_lock_l2_l3_portions_valid(struct pseudo_lock_region *plr,
> +					    struct pseudo_lock_portion *l2_p,
> +					    struct pseudo_lock_portion *l3_p)
> +{
> +	struct rdt_domain *l2_d, *l3_d;
> +	unsigned int l2_size, l3_size;
> +
> +	l2_d = rdt_find_domain(l2_p->r, l2_p->d_id, NULL);
> +	if (IS_ERR_OR_NULL(l2_d)) {
> +		rdt_last_cmd_puts("Cannot locate L2 cache domain\n");
> +		return -1;
> +	}
> +
> +	l3_d = rdt_find_domain(l3_p->r, l3_p->d_id, NULL);
> +	if (IS_ERR_OR_NULL(l3_d)) {
> +		rdt_last_cmd_puts("Cannot locate L3 cache domain\n");
> +		return -1;
> +	}
> +
> +	if (!cpumask_subset(&l2_d->cpu_mask, &l3_d->cpu_mask)) {
> +		rdt_last_cmd_puts("L2 and L3 caches need to be in same hierarchy\n");
> +		return -1;
> +	}
> +

Put that sentence above about L2 CPUs being constrained here - it is
easier when following the code.

> +	if (pseudo_lock_cstates_constrain(plr, &l2_d->cpu_mask)) {
> +		rdt_last_cmd_puts("Cannot limit C-states\n");
> +		return -1;
> +	}

Also, can that function call be last in this function so that you can
save yourself all the goto labels?

> +
> +	l2_size = rdtgroup_cbm_to_size(l2_p->r, l2_d, l2_p->cbm);
> +	l3_size = rdtgroup_cbm_to_size(l3_p->r, l3_d, l3_p->cbm);
> +
> +	if (l2_size > l3_size) {
> +		rdt_last_cmd_puts("L3 cache portion has to be same size or larger than L2 cache portion\n");
> +		goto err_size;
> +	}
> +
> +	plr->size = l2_size;
> +
> +	l2_size = get_cache_line_size(cpumask_first(&l2_d->cpu_mask),
> +				      l2_p->r->cache_level);
> +	l3_size = get_cache_line_size(cpumask_first(&l3_d->cpu_mask),
> +				      l3_p->r->cache_level);
> +	if (l2_size != l3_size) {
> +		rdt_last_cmd_puts("L2 and L3 caches have different coherency cache line sizes\n");
> +		goto err_line;
> +	}
> +
> +	plr->line_size = l2_size;
> +
> +	plr->cpu = cpumask_first(&l2_d->cpu_mask);
> +
> +	if (!cpu_online(plr->cpu)) {
> +		rdt_last_cmd_printf("CPU %u associated with cache not online\n",
> +				    plr->cpu);
> +		goto err_cpu;
> +	}
> +
> +	return 0;
> +
> +err_cpu:
> +	plr->line_size = 0;
> +	plr->cpu = 0;
> +err_line:
> +	plr->size = 0;
> +err_size:
> +	pseudo_lock_cstates_relax(plr);
> +	return -1;
> +}
> +
>  /**
>   * pseudo_lock_region_init - Initialize pseudo-lock region information
>   * @plr: pseudo-lock region
>   *
>   * Called after user provided a schemata to be pseudo-locked. From the
>   * schemata the &struct pseudo_lock_region is on entry already initialized
> - * with the resource, domain, and capacity bitmask. Here the
> + * with the resource(s), domain(s), and capacity bitmask(s). Here the
>   * provided data is validated and information required for pseudo-locking
>   * deduced, and &struct pseudo_lock_region initialized further. This
>   * information includes:
> @@ -355,13 +446,24 @@ static int pseudo_lock_single_portion_valid(struct pseudo_lock_region *plr,
>   * - a cpu associated with the cache instance on which the pseudo-locking
>   *   flow can be executed
>   *
> + * A user provides a schemata for a pseudo-locked region. This schemata may
> + * contain portions that span different resources, for example, a cache
> + * pseudo-locked region that spans L2 and L3 cache. After the schemata is
> + * parsed into portions it needs to be verified that the provided portions
> + * are valid with the following tests:
> + *
> + * - L2 only portion on system that has only L2 resource - OK
> + * - L3 only portion on any system that supports it - OK
> + * - L2 portion on system that has L3 resource - require L3 portion
> + **
> + *
>   * Return: 0 on success, <0 on failure. Descriptive error will be written
>   * to last_cmd_status buffer.
>   */
>  static int pseudo_lock_region_init(struct pseudo_lock_region *plr)
>  {
>  	struct rdt_resource *l3_resource = &rdt_resources_all[RDT_RESOURCE_L3];
> -	struct pseudo_lock_portion *p;
> +	struct pseudo_lock_portion *p, *n_p, *tmp;
>  	int ret;
>  
>  	if (list_empty(&plr->portions)) {
> @@ -397,8 +499,42 @@ static int pseudo_lock_region_init(struct pseudo_lock_region *plr)
>  			rdt_last_cmd_puts("Invalid resource or just L2 provided when L3 is required\n");
>  			goto out_region;
>  		}
> +	}
> +
> +	/*
> +	 * List is neither empty nor singular, process first and second portions
> +	 */
> +	p = list_first_entry(&plr->portions, struct pseudo_lock_portion, list);
> +	n_p = list_next_entry(p, list);
> +
> +	/*
> +	 * If the second portion is not also the last portion user provided
> +	 * more portions than can be supported.
> +	 */
> +	tmp = list_last_entry(&plr->portions, struct pseudo_lock_portion, list);
> +	if (n_p != tmp) {
> +		rdt_last_cmd_puts("Only two pseudo-lock portions supported\n");
> +		goto out_region;
> +	}
> +
> +	if (p->r->rid == RDT_RESOURCE_L2 && n_p->r->rid == RDT_RESOURCE_L3) {
> +		ret = pseudo_lock_l2_l3_portions_valid(plr, p, n_p);
> +		if (ret < 0)
> +			goto out_region;
> +		return 0;
> +	} else if (p->r->rid == RDT_RESOURCE_L3 &&
> +		   n_p->r->rid == RDT_RESOURCE_L2) {
> +		if (pseudo_lock_l2_l3_portions_valid(plr, n_p, p) == 0) {

		if (!pseudo_...

> +			/*
> +			 * Let L2 and L3 portions appear in order in the
> +			 * portions list in support of consistent output to
> +			 * user space.
> +			 */
> +			list_rotate_left(&plr->portions);
> +			return 0;
> +		}
>  	} else {
> -		rdt_last_cmd_puts("Multiple pseudo-lock portions unsupported\n");
> +		rdt_last_cmd_puts("Invalid combination of resources\n");
>  	}
>  
>  out_region:
> -- 
> 2.17.2
> 

-- 
Regards/Gruss,
    Boris.

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