Hi Tony,
On 9/25/2023 5:56 PM, Tony Luck wrote:
> On Mon, Sep 25, 2023 at 04:22:29PM -0700, Reinette Chatre wrote:
>> On 8/29/2023 4:44 PM, Tony Luck wrote:
...
>>> diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
>>> index 8334eeacfec5..2db1244ae642 100644
>>> --- a/include/linux/resctrl.h
>>> +++ b/include/linux/resctrl.h
>>> @@ -144,13 +144,18 @@ struct resctrl_membw {
>>> struct rdt_parse_data;
>>> struct resctrl_schema;
>>>
>>> +enum resctrl_scope {
>>> + RESCTRL_L3_CACHE,
>>> + RESCTRL_L2_CACHE,
>>> +};
>>
>> I'm curious why L3 appears before L2? This is not a big deal but
>> I think the additional indirection that this introduces is
>> not necessary. As you had in an earlier version this could be
>> RESCTRL_L2_CACHE = 2 and then the value can just be used directly
>> (after ensuring it is used in a valid context).
>
> I appear to have misundertood your earlier comments. I thought you
> didn't like my use of RESCTRL_L2_CACHE = 2, and RESCTRL_L3_CACHE = 3
> so that the could be passed directly to get_cpu_cacheinfo_id().
>
> But I see now the issue was "after ensuring it is used in a valid
> context". Are you looking for something like this:
Indeed. My concern with the earlier version was seeing a variable that
may contain any scope be used in a context where it can only represent
a cache level.
>
> enum resctrl_scope {
> RESCTRL_UNINITIALIZED_SCOPE = 0,
> RESCTRL_L2_CACHE = 2,
> RESCTRL_L3_CACHE = 3,
> RESCTRL_L3_NODE = 4,
> };
I do not think RESCTRL_UNINITIALIZED_SCOPE is required (perhaps getting too
defensive?) but adding it would surely not do harm and indeed make it
obvious how the uninitialized case is handled. I am not familiar with
customs in this regard and would be ok either way. You can decide what
works best for you.
About the new name RESCTRL_L3_NODE. It is not clear to me why "L3" is
in the name.
>
> static int get_domain_id_from_scope(int cpu, enum resctrl_scope scope)
> {
> switch (scope) {
> case RESCTRL_L2_CACHE:
> case RESCTRL_L3_CACHE:
> return get_cpu_cacheinfo_id(cpu, scope);
> case RESCTRL_NODE:
> return cpu_to_node(cpu);
(oh - maybe the earlier RESCTRL_L3_NODE was a typo?)
> default:
> case RESCTRL_UNINITIALIZED_SCOPE:
> WARN_ON_ONCE(1);
> return -1;
> }
>
> return -1;
> }
>
I'll leave it to you to decide if you want to use
RESCTRL_UNINITIALIZED_SCOPE. If you do decide to keep it
could you please let the "default" case be the last one?
>>
>>> +
>>> /**
>>> * struct rdt_resource - attributes of a resctrl resource
>>> * @rid: The index of the resource
>>> * @alloc_capable: Is allocation available on this machine
>>> * @mon_capable: Is monitor feature available on this machine
>>> * @num_rmid: Number of RMIDs available
>>> - * @cache_level: Which cache level defines scope of this resource
>>> + * @scope: Scope of this resource
>>> * @cache: Cache allocation related data
>>> * @membw: If the component has bandwidth controls, their properties.
>>> * @domains: All domains for this resource
>>> @@ -168,7 +173,7 @@ struct rdt_resource {
>>> bool alloc_capable;
>>> bool mon_capable;
>>> int num_rmid;
>>> - int cache_level;
>>> + enum resctrl_scope scope;
>>> struct resctrl_cache cache;
>>> struct resctrl_membw membw;
>>> struct list_head domains;
>>> diff --git a/arch/x86/kernel/cpu/resctrl/core.c b/arch/x86/kernel/cpu/resctrl/core.c
>>> index 030d3b409768..0d3bae523ecb 100644
>>> --- a/arch/x86/kernel/cpu/resctrl/core.c
>>> +++ b/arch/x86/kernel/cpu/resctrl/core.c
>>> @@ -65,7 +65,7 @@ struct rdt_hw_resource rdt_resources_all[] = {
>>> .r_resctrl = {
>>> .rid = RDT_RESOURCE_L3,
>>> .name = "L3",
>>> - .cache_level = 3,
>>> + .scope = RESCTRL_L3_CACHE,
>>> .domains = domain_init(RDT_RESOURCE_L3),
>>> .parse_ctrlval = parse_cbm,
>>> .format_str = "%d=%0*x",
>>> @@ -79,7 +79,7 @@ struct rdt_hw_resource rdt_resources_all[] = {
>>> .r_resctrl = {
>>> .rid = RDT_RESOURCE_L2,
>>> .name = "L2",
>>> - .cache_level = 2,
>>> + .scope = RESCTRL_L2_CACHE,
>>> .domains = domain_init(RDT_RESOURCE_L2),
>>> .parse_ctrlval = parse_cbm,
>>> .format_str = "%d=%0*x",
>>> @@ -93,7 +93,7 @@ struct rdt_hw_resource rdt_resources_all[] = {
>>> .r_resctrl = {
>>> .rid = RDT_RESOURCE_MBA,
>>> .name = "MB",
>>> - .cache_level = 3,
>>> + .scope = RESCTRL_L3_CACHE,
>>> .domains = domain_init(RDT_RESOURCE_MBA),
>>> .parse_ctrlval = parse_bw,
>>> .format_str = "%d=%*u",
>>> @@ -105,7 +105,7 @@ struct rdt_hw_resource rdt_resources_all[] = {
>>> .r_resctrl = {
>>> .rid = RDT_RESOURCE_SMBA,
>>> .name = "SMBA",
>>> - .cache_level = 3,
>>> + .scope = RESCTRL_L3_CACHE,
>>> .domains = domain_init(RDT_RESOURCE_SMBA),
>>> .parse_ctrlval = parse_bw,
>>> .format_str = "%d=%*u",
>>> @@ -487,6 +487,21 @@ static int arch_domain_mbm_alloc(u32 num_rmid, struct rdt_hw_domain *hw_dom)
>>> return 0;
>>> }
>>>
>>> +static int get_domain_id_from_scope(int cpu, enum resctrl_scope scope)
>>> +{
>>> + switch (scope) {
>>> + case RESCTRL_L3_CACHE:
>>> + return get_cpu_cacheinfo_id(cpu, 3);
>>> + case RESCTRL_L2_CACHE:
>>> + return get_cpu_cacheinfo_id(cpu, 2);
>>> + default:
>>> + WARN_ON_ONCE(1);
>>> + break;
>>> + }
>>> +
>>> + return -1;
>>> +}
>>
>> Looking ahead at the next patch some members of rdt_resources_all[]
>> are left with a default "0" initialization of mon_scope that is a
>> valid scope of RESCTRL_L3_CACHE in this implementation that would
>> not be caught with defensive code like above. For the above to catch
>> a case like this I think that there should be some default
>> initialization - but if you do move to something like you
>> had in v3 then this may not be necessary. If the L2 scope is 2,
>> L3 scope is 3, node scope is 4, then no initialization will be zero
>> and the above default can more accurately catch failure cases.
>
> See above (with a defensive enum constant that has the value 0).
>
>>
>>> +
>>> /*
>>> * domain_add_cpu - Add a cpu to a resource's domain list.
>>> *
>>> @@ -502,7 +517,7 @@ static int arch_domain_mbm_alloc(u32 num_rmid, struct rdt_hw_domain *hw_dom)
>>> */
>>> static void domain_add_cpu(int cpu, struct rdt_resource *r)
>>> {
>>> - int id = get_cpu_cacheinfo_id(cpu, r->cache_level);
>>> + int id = get_domain_id_from_scope(cpu, r->scope);
>>> struct list_head *add_pos = NULL;
>>> struct rdt_hw_domain *hw_dom;
>>> struct rdt_domain *d;
>>> @@ -552,7 +567,7 @@ static void domain_add_cpu(int cpu, struct rdt_resource *r)
>>>
>>> static void domain_remove_cpu(int cpu, struct rdt_resource *r)
>>> {
>>> - int id = get_cpu_cacheinfo_id(cpu, r->cache_level);
>>> + int id = get_domain_id_from_scope(cpu, r->scope);
>>> struct rdt_hw_domain *hw_dom;
>>> struct rdt_domain *d;
>>>
>>> diff --git a/arch/x86/kernel/cpu/resctrl/pseudo_lock.c b/arch/x86/kernel/cpu/resctrl/pseudo_lock.c
>>> index 458cb7419502..e79324676f57 100644
>>> --- a/arch/x86/kernel/cpu/resctrl/pseudo_lock.c
>>> +++ b/arch/x86/kernel/cpu/resctrl/pseudo_lock.c
>>> @@ -279,6 +279,7 @@ static void pseudo_lock_region_clear(struct pseudo_lock_region *plr)
>>> static int pseudo_lock_region_init(struct pseudo_lock_region *plr)
>>> {
>>> struct cpu_cacheinfo *ci;
>>> + int cache_level;
>>> int ret;
>>> int i;
>>>
>>> @@ -296,8 +297,20 @@ static int pseudo_lock_region_init(struct pseudo_lock_region *plr)
>>>
>>> plr->size = rdtgroup_cbm_to_size(plr->s->res, plr->d, plr->cbm);
>>>
>>> + switch (plr->s->res->scope) {
>>> + case RESCTRL_L3_CACHE:
>>> + cache_level = 3;
>>> + break;
>>> + case RESCTRL_L2_CACHE:
>>> + cache_level = 2;
>>> + break;
>>> + default:
>>> + WARN_ON_ONCE(1);
>>> + return -ENODEV;
>>> + }
>>
>> I think this can be simplified without the indirection - a simplified
>> WARN can just test for valid values of plr->s->res->scope directly
>> (exit on failure) and then it can be used directly in the code below
>> when the enum value corresponds to a cache level.
>
> Is this what you want here?
>
> if (plr->s->res->scope != RESCTRL_L2_CACHE &&
> plr->s->res->scope != RESCTRL_L3_CACHE) {
> WARN_ON_ONCE(1);
> return -ENODEV;
> }
Something like this, yes. It could be simplified more with a:
/* Just to get line length shorter: */
enum resctrl_scope scope = plr->s->res->scope; /* or cache_level? */
if (WARN_ON_ONCE(scope != RESCTRL_L2_CACHE && scope != RESCTRL_L3_CACHE))
return -ENODEV;
Reinette
