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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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