Re: [PATCH v6 2/3] x86/resctrl: Use total bandwidth for mba_MBps option when local isn't present

[Peter Newman <peternewman@google.com>]

On Thu, Dec 7, 2023 at 11:56 AM Tony Luck <tony.luck@intel.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@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, 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@google.com>