linux-kernel - Re: [PATCH v6 2/3] x86/resctrl: Use total bandwidth for mba

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Message-ID: <CALPaoCgR5qNsSegKLzg2g2eE8EgQB9vixAdDOryQOr8HQ+CPAw@mail.gmail.com>
Date:   Fri, 8 Dec 2023 10:26:06 -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 2/3] x86/resctrl: Use total bandwidth for mba_MBps
 option when local isn't present

On Thu, Dec 7, 2023 at 11:56 AM Tony Luck <tony.luck@...el.com> wrote:
>
> On Intel systems the memory bandwidth monitoring events are
> independently enumerated. It is possible for a system to support
> total memory bandwidth monitoring, but not support local bandwidth
> monitoring. On such a system a user could not enable mba_sc mode.
> Users will see this highly unhelpful error message from mount:
>
>  # mount -t resctrl -o mba_MBps resctrl /sys/fs/resctrl
>  mount: /sys/fs/resctrl: wrong fs type, bad option, bad superblock on
>  resctrl, missing codepage or helper program, or other error.
>  dmesg(1) may have more information after failed mount system call.
>
> dmesg(1) does not provide any additional information.
>
> Modify the existing "mba_MBps" mount option to switch to total bandwidth
> monitoring if local monitoring is not available.
>
> Signed-off-by: Tony Luck <tony.luck@...el.com>
> ---
>  arch/x86/kernel/cpu/resctrl/rdtgroup.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> index 5f64a0b2597c..7410513db45a 100644
> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> @@ -2725,6 +2725,8 @@ static int rdt_parse_param(struct fs_context *fc, struct fs_parameter *param)
>                         return -EINVAL;
>                 if (is_mbm_local_enabled())
>                         ctx->enable_mba_mbps_local = true;
> +               else if (is_mbm_total_enabled())
> +                       ctx->enable_mba_mbps_total = true;
>                 else
>                         return -EINVAL;
>                 return 0;
> --
> 2.41.0
>

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