linux-kernel - Re: [PATCH v6 3/3] x86/resctrl: Add new "mba_MBps

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Date:   Fri, 8 Dec 2023 11:22:33 -0800
From:   Peter Newman <peternewman@...gle.com>
To:     Tony Luck <tony.luck@...el.com>
Cc:     Fenghua Yu <fenghua.yu@...el.com>,
        Reinette Chatre <reinette.chatre@...el.com>,
        Jonathan Corbet <corbet@....net>,
        Shuah Khan <skhan@...uxfoundation.org>, x86@...nel.org,
        Shaopeng Tan <tan.shaopeng@...itsu.com>,
        James Morse <james.morse@....com>,
        Jamie Iles <quic_jiles@...cinc.com>,
        Babu Moger <babu.moger@....com>,
        Randy Dunlap <rdunlap@...radead.org>,
        linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
        patches@...ts.linux.dev
Subject: Re: [PATCH v6 3/3] x86/resctrl: Add new "mba_MBps_event" mount option
 to documentation

On Thu, Dec 7, 2023 at 11:56 AM Tony Luck <tony.luck@...el.com> wrote:
>
> New mount option may be used to choose a specific memory bandwidth
> monitoring event to feed the MBA Software Controller(mba_sc) feedback
> loop.
>
> Signed-off-by: Tony Luck <tony.luck@...el.com>
> ---
>  Documentation/arch/x86/resctrl.rst | 16 ++++++++++++++--
>  1 file changed, 14 insertions(+), 2 deletions(-)
>
> diff --git a/Documentation/arch/x86/resctrl.rst b/Documentation/arch/x86/resctrl.rst
> index a6279df64a9d..a0c521db6786 100644
> --- a/Documentation/arch/x86/resctrl.rst
> +++ b/Documentation/arch/x86/resctrl.rst
> @@ -35,7 +35,8 @@ about the feature from resctrl's info directory.
>
>  To use the feature mount the file system::
>
> - # mount -t resctrl resctrl [-o cdp[,cdpl2][,mba_MBps][,debug]] /sys/fs/resctrl
> + # mount -t resctrl resctrl [-o cdp[,cdpl2][,mba_MBps] \
> + [,mba_MBps_event=[mbm_local_bytes|mbm_total_bytes]][,debug]] /sys/fs/resctrl
>
>  mount options are:
>
> @@ -45,7 +46,12 @@ mount options are:
>         Enable code/data prioritization in L2 cache allocations.
>  "mba_MBps":
>         Enable the MBA Software Controller(mba_sc) to specify MBA
> -       bandwidth in MBps
> +       bandwidth in MBps. Defaults to using MBM local bandwidth,
> +       but will use total bandwidth on systems that do not support
> +       local bandwidth monitoring.
> +"mba_MBps_event=[mbm_local_bytes|mbm_total_bytes]":
> +       Enable the MBA Software Controller(mba_sc) with a specific
> +       MBM event as input to the feedback loop.
>  "debug":
>         Make debug files accessible. Available debug files are annotated with
>         "Available only with debug option".
> @@ -538,6 +544,12 @@ where as user can switch to the "MBA software controller" mode using
>  a mount option 'mba_MBps'. The schemata format is specified in the below
>  sections.
>
> +By default the software feedback mechanism uses measurement of local
> +memory bandwidth to make adjustments to throttling levels. If a system
> +is running applications with poor NUMA locality users may want to use
> +the "mba_MBps_event=mbm_total_bytes" mount option which will use total
> +memory bandwidth measurements instead of local.
> +
>  L3 schemata file details (code and data prioritization disabled)
>  ----------------------------------------------------------------
>  With CDP disabled the L3 schemata format is::
> --
> 2.41.0
>

for content:

Reviewed-by: Peter Newman <peternewman@...gle.com>