Re: [PATCH v3 15/38] x86/resctrl: Move monitor exit work to a restrl exit call

[James Morse <james.morse@arm.com>]

Hi Reinette,

On 28/06/2024 17:46, Reinette Chatre wrote:
> On 6/14/24 8:00 AM, James Morse wrote:
>> rdt_put_mon_l3_config() is called via the architecture's
>> resctrl_arch_exit() call, and appears to free the rmid_ptrs[]
>> and closid_num_dirty_rmid[] arrays. In reality this code is marked
>> __exit, and is removed by the linker as resctl can't be built
>> as a module.
>>
>> To separate the filesystem and architecture parts of resctrl,
>> this free()ing work needs to be triggered by the filesystem,
>> as these structures belong to the filesystem code.
>>
>> Rename rdt_put_mon_l3_config() resctrl_mon_resource_exit()
>> and call it from resctrl_exit(). The kfree() is currently
>> dependent on r->mon_capable. resctrl_mon_resource_init()

> resctrl_mon_resource_init() does not exist at this point making
> this motivation difficult to follow.

Right - I re-ordered the patches to make the diffs simpler. I'll drop this paragraph.


>> takes no arguments, so resctrl_mon_resource_exit() shouldn't
>> take any either. Add the check to dom_data_exit(), making it
>> take the resource as an argument. This makes it more symmetrical
>> with dom_data_init().

>> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
>> index 3e5375c365e6..7d6aebce75c1 100644
>> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
>> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
>> @@ -965,10 +965,12 @@ static int dom_data_init(struct rdt_resource *r)
>>       return err;
>>   }
>>   -static void __exit dom_data_exit(void)
>> +static void dom_data_exit(struct rdt_resource *r)
>>   {
>> -    mutex_lock(&rdtgroup_mutex);
>> +    if (!r->mon_capable)
>> +        return;
>>   +    mutex_lock(&rdtgroup_mutex);
> 
> I know there has been a bit of back&forth on whether the mutex is needed
> here. With this change moving dom_data_exit() out from __exit I think
> the locking should aim to be consistent with existing runtime
> and thus the check of r->mon_capable should be with mutex held. Having
> this little snippet outside mutex will just cause confusion.

> Do you have motivation for needing this be done outside of mutex?

Just to avoid sleeping - then returning having done nothing.


> I think it
> ended up this way with this patch aiming to keep existing flow exactly,
> but that ended up as convenience in a flow where mutex was not really
> needed at all.

Sure - I don't think it matters either way. Its not a path where performance matters.
The property is read-only from when resctrl_init() is called. I'll make it look like
resctrl_offline_domain().


Thanks,

James