Re: [PATCH V2 09/10] x86/resctrl: Pseudo-lock portions of multiple resources

Reinette Chatre
2019-08-07T19:23:34Z

Hi Borislav,

On 8/7/2019 8:25 AM, Borislav Petkov wrote:
> 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@intel.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.

Will do.

>
>> + 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?

I do not fully understand this proposal. All those goto labels take care
of the the different failures that can be encountered during the
initialization of the pseudo-lock region. Each initialization failure is
associated with a goto where it jumps to the cleanup path. The
initialization starts with the constraining of the c-states
(initializing plr->pm_reqs), but if I move that I think it will not
reduce the goto labels, just change the order because of the other
initialization done (plr->size, plr->line_size, plr->cpu).

>
>> +
>> + 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_...
>

Will do. Seems that I need to check all my code for this pattern.

>> + /*
>> + * 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
>>
>

Thank you very much

Reinette