Re: [PATCH v8 02/21] x86/resctrl: Remove the limit on the number of CLOSID

[James Morse]

Hi Shaopeng Tan,

On 25/04/2025 03:56, Shaopeng Tan (Fujitsu) wrote:
>> From: Amit Singh Tomar <amitsinght@xxxxxxxxxxx>
>>
>> Resctrl allocates and finds free CLOSID values using the bits of a u32.
>> This restricts the number of control groups that can be created by user-space.
>>
>> MPAM has an architectural limit of 2^16 CLOSID values, Intel x86 could be
>> extended beyond 32 values. There is at least one MPAM platform which
>> supports more than 32 CLOSID values.
>>
>> Replace the fixed size bitmap with calls to the bitmap API to allocate an array of
>> a sufficient size.
>>
>> ffs() returns '1' for bit 0, hence the existing code subtracts 1 from the index to
>> get the CLOSID value. find_first_bit() returns the bit number which does not
>> need adjusting.

>> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> index 776c8e347654..4e0308040c6e 100644
>> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c

>> @@ -2765,20 +2775,22 @@ static int rdt_get_tree(struct fs_context *fc)
>>  		goto out_ctx;
>>  	}

> Not relevant to this patch, but some of the code around here needs improvement. Maybe consider fixing it together?

>        ret = schemata_list_create();
>        if (ret) {
> -              schemata_list_destroy();
> -              goto out_ctx;
> +             goto out_schemata_free;
>        }

Hmmm, that doesn't make a difference, but it does save a line. As I'm not changing that
code in this series, I don't want to touch it as part of this series. (its already getting
too big!)

It got written like that because list_create() doesn't do all the cleanup when it fails,
this makes it the odd one out..

If you think this version is better, please send a patch!


Thanks,

James