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

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Message-ID: <ZwcIkf_oy2oKByNu@agluck-desk3.sc.intel.com>
Date: Wed, 9 Oct 2024 15:49:53 -0700
From: Tony Luck <tony.luck@...el.com>
To: Babu Moger <babu.moger@....com>
Cc: corbet@....net, fenghua.yu@...el.com, reinette.chatre@...el.com,
	tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
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Subject: Re: [PATCH v8 08/25] x86/resctrl: Introduce interface to display
 number of monitoring counters

On Wed, Oct 09, 2024 at 12:39:33PM -0500, Babu Moger wrote:
> +"num_mbm_cntrs":
> +	The number of monitoring counters available for assignment when the
> +	architecture supports mbm_cntr_assign mode.

It's not obvious (to me) how these counters work. When I create
a group with both local and total monitoring enabled, does that
use up two counters (even though I only used up one RMID)?

Are the counters multi-purpose. E.g. if I disable local counting
on all groups, are the freed-up counters available for use to
count total bandwidth on some additional groups?

>From the examples it looks like if there are free counters
available when user does mkdir, then they will be assigned
to the new rdtgroup. If only one counter is free, does it
get assigned to local or total?

Thanks

-Tony