Re: 32bit resctrl? (was Re: [PATCH v2] fs/resctrl: fix domid loss precision issue)

[Reinette Chatre]

On 3/14/2024 5:04 PM, Peter Newman wrote:
> On Thu, Mar 14, 2024 at 8:25 AM Reinette Chatre
> <reinette.chatre@xxxxxxxxx> wrote:
>>
>> +x86 maintainers, Tony, Babu, Peter
>>
>> Hi Everybody,
>>
>> On 3/12/2024 12:53 AM, Rex Nie wrote:
>>> Below statement from mkdir_mondata_subdir function will loss precision,
>>> because it assigns int to 14 bits bitfield.
>>>       priv.u.domid = d->id;
>>>
>>> On some platforms(e.g.,x86), the max cache_id is the amount of L3 caches,
>>> so it is not in the range of 0x3fff. But some platforms use higher
>>> cache_id, e.g., arm uses cache_id as locator for cache MSC. This will
>>> cause below issue if cache_id > 0x3fff likes:
>>> /sys/fs/resctrl/mon_groups/p1/mon_data/mon_L3_1048564 # cat llc_occupancy
> 
> This domain ID seems unreadable in decimal and I'm wondering whether
> it's the best value to use to identify the domain. Does this system
> have over 1 million L3 domains?

I propose that Rex includes the information about Arm's cache IDs [1]
in future changelogs.

Reinette


[1] https://lore.kernel.org/lkml/KL1PR0601MB577303C9D0B1247436BB06F8E6242@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/