Re: [PATCH v9 6/9] x86/resctrl: Add "mba_MBps_event" file to ctrl_mon directories

Luck, Tony
2024-11-21T17:42:15Z

On Tue, Nov 19, 2024 at 08:03:06PM -0800, Reinette Chatre wrote:
> Hi Tony,
>
> On 11/13/24 4:17 PM, Tony Luck wrote:
> > The "mba_MBps" mount option provides an alternate method to
> > control memory bandwidth. Instead of specifying allowable
> > bandwidth as a percentage of maximum possible, the user
> > provides a MiB/s limit value.
> >
> > Historically the limit was enforced by a feedback loop from
>
> "Historically the limit was enforced" no history needed since
> this is still the case at the time of this patch.
>
> > the measure local bandwidth to adjust the memory bandwidth
> > allocation controls.
>
> I am not sure what is meant by "a feedback loop from the measure
> local bandwidth" (that was copy&pasted to next patch).

Dropped the whole of the "Historically" paragraph.
>
> >
> > In preparation to allow the user to pick the memory bandwidth
> > monitoring event used as input to the feedback loop, provide
> > a file in each ctrl_mon group directory that shows the event
>
> In the documentation the custom is to use CTRL_MON.

Fixed here (and in several other places in the series).

> > currently in use.
>
> Much better changelog. I think it will help to add a snippet that
> mentions the file is only visible to user space if resctrl
> was mounted with mba_MBps, and thus only visible when mba_sc is
> enabled, and thus reinforcing that this maintains the contract
> that rdtgrp->mba_mbps_event is only accessed when mba_sc is enabled.

Added text to commit message about this file only being visible
when the "mba_MBps" mount option is in use.

> >
> > Suggested-by: Reinette Chatre <reinette.chatre@intel.com>
> > Signed-off-by: Tony Luck <tony.luck@intel.com>
> > ---
>
> Reinette

-Tony