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References: <20231201214737.104444-1-tony.luck@intel.com> <20231207195613.153980-1-tony.luck@intel.com>
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In-Reply-To: <20231207195613.153980-3-tony.luck@intel.com>
From:   Peter Newman <peternewman@google.com>
Date:   Fri, 8 Dec 2023 10:26:06 -0800
Message-ID: <CALPaoCgR5qNsSegKLzg2g2eE8EgQB9vixAdDOryQOr8HQ+CPAw@mail.gmail.com>
Subject: Re: [PATCH v6 2/3] x86/resctrl: Use total bandwidth for mba_MBps
 option when local isn't present
To:     Tony Luck <tony.luck@intel.com>
Cc:     Fenghua Yu <fenghua.yu@intel.com>,
        Reinette Chatre <reinette.chatre@intel.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Shuah Khan <skhan@linuxfoundation.org>, x86@kernel.org,
        Shaopeng Tan <tan.shaopeng@fujitsu.com>,
        James Morse <james.morse@arm.com>,
        Jamie Iles <quic_jiles@quicinc.com>,
        Babu Moger <babu.moger@amd.com>,
        Randy Dunlap <rdunlap@infradead.org>,
        linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
        patches@lists.linux.dev
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On Thu, Dec 7, 2023 at 11:56=E2=80=AFAM Tony Luck <tony.luck@intel.com> wro=
te:
>
> 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@intel.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, s=
truct fs_parameter *param)
>                         return -EINVAL;
>                 if (is_mbm_local_enabled())
>                         ctx->enable_mba_mbps_local =3D true;
> +               else if (is_mbm_total_enabled())
> +                       ctx->enable_mba_mbps_total =3D true;
>                 else
>                         return -EINVAL;
>                 return 0;
> --
> 2.41.0
>

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