Re: [PATCH v11 11/23] x86/resctrl: Introduce mbm_cntr_cfg to track assignable counters at domain

[Dave Martin]

Hi,

On Mon, Feb 10, 2025 at 10:10:26AM -0800, Reinette Chatre wrote:
> Hi Babu,
> 
> On 2/7/25 10:23 AM, Moger, Babu wrote:
> > On 2/5/2025 5:57 PM, Reinette Chatre wrote:
> >> On 1/22/25 12:20 PM, Babu Moger wrote:

[...]

> >>> MBM events of a monitoring group is tracked by hardware. Such queries
> >>> are acceptable because of a very small number of assignable counters.
> >>
> >> It is not obvious what "very small number" means. Is it possible to give
> >> a range to help reader understand the motivation?
> > 
> > How about?
> > 
> > MBM events of a monitoring group is tracked by hardware. Such queries
> > are acceptable because of a very small number of assignable counters(32 to 64).
> 
> Yes, thank you. This helps to understand the claim.
> 
> Reinette

Do these queries only happen when userspace reads an mbm_assign_control
file?

It might be worth documenting somewhere that writing and (especially)
reading an mbm_assign_control file is not intended to be super-fast.

It feels like userspace should not generally rely on reading
mbm_assign_control files except for diagnostic purposes, or occasional
read-modify-write transformations.  Or do expect some other usage model
that makes this a hotter path?

Cheers
---Dave