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

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Message-ID: <Zwlj5TQxZphcuDSR@agluck-desk3.sc.intel.com>
Date: Fri, 11 Oct 2024 10:44:05 -0700
From: Tony Luck <tony.luck@...el.com>
To: "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

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.

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).

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?

-Tony