linux-kernel - RE: [PATCH v12 18/26] x86/resctrl: Add default MBM event configurations for mbm_cntr

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Message-ID: <DS7PR11MB60771546582C59A917647239FCB22@DS7PR11MB6077.namprd11.prod.outlook.com>
Date: Tue, 15 Apr 2025 19:25:58 +0000
From: "Luck, Tony" <tony.luck@...el.com>
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Subject: RE: [PATCH v12 18/26] x86/resctrl: Add default MBM event
 configurations for mbm_cntr_assign mode

> By default, each resctrl group supports two MBM events: mbm_total_bytes
> and mbm_local_bytes. These represent total and local memory bandwidth
> monitoring, respectively. Each event corresponds to a specific MBM
> configuration. Use these default configurations to set up the counters
> during mount. Allow users to modify the configurations as needed after
> initialization.

I think an update to this part of the resctrl.rst documentation is somewhat
overdue:

        In a MON group these files provide a read out of the current
        value of the event for all tasks in the group. In CTRL_MON groups
        these files provide the sum for all tasks in the CTRL_MON group
        and all tasks in MON groups. Please see example section for more
        details on usage.

The sentence about CTRL_MON groups providing the sum for all tasks
in the child MON groups is only true if counters are assigned to all of
those MON groups. What mon_event_count() actually does is to
return success if any of the CTRL_MON or child MON groups succeeded
with the count being the sum of all the successes.

-Tony