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

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Message-ID: <SJ1PR11MB60833A1571413763DE36B538FC442@SJ1PR11MB6083.namprd11.prod.outlook.com>
Date: Mon, 14 Oct 2024 17:49:02 +0000
From: "Luck, Tony" <tony.luck@...el.com>
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Subject: RE: [PATCH v8 08/25] x86/resctrl: Introduce interface to display
 number of monitoring counters

> >> I.e. the user who chose this simply gave up being able to
> >> read total bandwidth on domain 1, but didn't get an extra
> >> counter in exchange for this sacrifice. That doesn't seem
> >> like a good deal.
> >
> > As Babu mentioned earlier, this seems equivalent to the existing
> > CLOSid management. For example, if a user assigns only CPUs
> > from one domain to a resource group, it does not free up the
> > CLOSID to create a new resource group dedicated to other domain(s).

I hadn't considered the case where a user is assigning CPUs to resctrl
groups instead of assigning tasks. With that context this makes sense
to me now.  Thanks.


> Thanks for the confirmation here.
>
> I was wondering if this works differently on Intel. I was trying to figure
> out on 2 socket intel system if we can create two separate resctrl groups
> sharing the same CLOSID (one group using CLOSID 1 on socket 0 and another
> group CLOSID 1 socket 1). No. We cannot do that.
>
> Even though hardware supports separate allocation for each domain, resctrl
> design does not support that.

So CLOSIDs and counters are blanket assigned across all domains. I understand
that now.

Back to my question of why complicate code and resctrl files by providing a
mechanism to enable event counters differently per-domain.

"0=tl;1=_" requires allocation of the same counters as "0=tl;1=tl" or
"0=t;1=l"

What advantage does it have over skipping the per-domain list and
just providing a single value for all domains? You clearly expect this
will be a common user request since you implemented the "*" means
apply to all domains.

-Tony