linux-kernel - Re: [PATCH v8 08/25] x86/resctrl: Introduce interface to display number of monitoring counters

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Message-ID: <8af0ce3a-1327-3ffc-ac5c-e495f9cdf5d0@amd.com>
Date: Fri, 11 Oct 2024 15:49:48 -0500
From: "Moger, Babu" <bmoger@....com>
To: Tony Luck <tony.luck@...el.com>, "Moger, Babu" <babu.moger@....com>
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Subject: Re: [PATCH v8 08/25] x86/resctrl: Introduce interface to display
 number of monitoring counters

Hi Tony,

On 10/11/2024 12:44 PM, Tony Luck wrote:
> On Thu, Oct 10, 2024 at 03:32:08PM -0500, Moger, Babu wrote:
>>> # cat /sys/fs/resctrl/info/L3_MON/mbm_assign_control
>>> //0=tl;1=tl;
>>>
>>> there aren't separate counts from each of domain 0 and domain 1.
>>
>> Yes. There is. Each domain has its own count. I am not sure about your config.
> 
> I've been reading the code and see better now.
> 
> There are a bunch (32) of counters per domain.
> 
> But you have a system-wide allocator. So when making
> a group you may allocate counters 2 and 3 for total
> and local respectively. Then configure the local instance
> of counter 2 on each domain (recording that in the per-domain
> bitmap) for total bandwidth. Ditto for counter 3 instances
> on each domain.

Yes. That is correct.
> 
> If the user updates the configuration to stop counting
> on domain 1. Then the per-domain bitmap is updated to
> show counters 2 and 3 are no longer in use on this domain.
> But those counters aren't freed (because domain 0 is still
> using them).

Yes. Correct.


> 
> Is there some hardware limitation that would prevent
> re-using domain 1 counters 2 & 3 for some other group (RMID)?
> 
> Or is this just a s/w implementation detail because
> you have a system wide allocator for counters?
> 

There is no hardware limitation. It is how resctrl is designed.
In case of Intel(with two sockets, 16 CLOSIDs), You can only create 16 
groups. Each group will have two domains(domain 0 for socket 0 and 
domain 1 for socket 1).

# cat schemata
     MB:0=100;1=100
     L3:0=ffff;1=ffff;


We may have to think of addressing this sometime in the future.
-- 
- Babu Moger