Re: [PATCH 5/7] x86/resctrl: Add interface to enable/disable SDCIAE

[Reinette Chatre]

Hi Babu,

On 9/18/24 1:10 PM, Moger, Babu wrote:
> On 9/13/24 15:51, Reinette Chatre wrote:
>> On 8/16/24 9:16 AM, Babu Moger wrote:

...

>>> +        if (enable) {
>>> +            ret = closid_alloc_sdciae(r);
>>> +            if (ret < 0) {
>>> +                rdt_last_cmd_puts("SDCIAE CLOSID is not available\n");
>>> +                goto out_sdciae;
>>> +            }
>>> +        } else {
>>> +            sdciae_closid = get_sdciae_closid(r);
>>> +            closid_free(sdciae_closid);
>>> +        }
>>
>>
>>> +
>>> +        ret = resctrl_arch_set_sdciae_enabled(RDT_RESOURCE_L3, enable);
>>
>> I assume that once SDCIAE is enabled the I/O traffic will start flowing to
>> whatever
>> was the last CBM of the max CLOSID? Is this intended or should there be
>> some default
>> CBM that this feature should start with?
> 
> It will start with whatever the last CBM for max CLOSID.

This seems arbitrary based on whatever allocation the previous resource group
using the CLOSID has. When a new resource group is created resctrl ensures
that it is created with all usable allocations, see rdtgroup_init_cat().
Letting cache injection start with whatever allocation remnant programmed
in a register does not seem ideal. What if, for example, after that resource
group was removed, a new exclusive resource group was created that overlaps
with that allocation? 

Reinette