Re: [PATCH v15 28/34] fs/resctrl: Introduce mbm_assign_on_mkdir to enable assignments on mkdir

[Peter Newman <peternewman@google.com>]

Hi Babu,

On Wed, Jul 9, 2025 at 12:22 AM Babu Moger <babu.moger@amd.com> wrote:
>
> The "mbm_event" counter assignment mode allows users to assign a hardware
> counter to an RMID, event pair and monitor the bandwidth as long as it is
> assigned.
>
> Introduce a user-configurable option that determines if a counter will
> automatically be assigned to an RMID, event pair when its associated
> monitor group is created via mkdir.
>
> Suggested-by: Peter Newman <peternewman@google.com>
> Signed-off-by: Babu Moger <babu.moger@amd.com>
> ---
> v15: Fixed the static checker warning in resctrl_mbm_assign_on_mkdir_write() reported in
>      https://lore.kernel.org/lkml/dd4a1021-b996-438e-941c-69dfcea5f22a@intel.com/
>
> v14: Added rdtgroup_mutex in resctrl_mbm_assign_on_mkdir_show().
>      Updated resctrl.rst for clarity.
>      Fixed squashing of few previous changes.
>      Added more code documentation.
>
> v13: Added Suggested-by tag.
>      Resolved conflicts caused by the recent FS/ARCH code restructure.
>      The rdtgroup.c/monitor.c file has now been split between the FS and ARCH directories.
>
> v12: New patch. Added after the discussion on the list.
>      https://lore.kernel.org/lkml/CALPaoCh8siZKjL_3yvOYGL4cF_n_38KpUFgHVGbQ86nD+Q2_SA@mail.gmail.com/
> ---
>  Documentation/filesystems/resctrl.rst | 16 ++++++++++
>  fs/resctrl/monitor.c                  |  2 ++
>  fs/resctrl/rdtgroup.c                 | 43 +++++++++++++++++++++++++++
>  include/linux/resctrl.h               |  3 ++
>  4 files changed, 64 insertions(+)
>
> diff --git a/Documentation/filesystems/resctrl.rst b/Documentation/filesystems/resctrl.rst
> index 06c8c08d0341..f9e9a8a66cae 100644
> --- a/Documentation/filesystems/resctrl.rst
> +++ b/Documentation/filesystems/resctrl.rst
> @@ -354,6 +354,22 @@ with the following files:
>           # cat /sys/fs/resctrl/info/L3_MON/event_configs/mbm_total_bytes/event_filter
>            local_reads,local_non_temporal_writes
>
> +"mbm_assign_on_mkdir":
> +       Determines if a counter will automatically be assigned to an RMID, event pair
> +       when its associated monitor group is created via mkdir. It is enabled by default
> +       on boot and users can disable by writing to the interface.
> +
> +       "0":
> +               Auto assignment is disabled.
> +       "1":
> +               Auto assignment is enabled.
> +
> +       Example::
> +
> +         # echo 0 > /sys/fs/resctrl/info/L3_MON/mbm_assign_on_mkdir
> +         # cat /sys/fs/resctrl/info/L3_MON/mbm_assign_on_mkdir
> +         0
> +
>  "max_threshold_occupancy":
>                 Read/write file provides the largest value (in
>                 bytes) at which a previously used LLC_occupancy
> diff --git a/fs/resctrl/monitor.c b/fs/resctrl/monitor.c
> index 0722e72f6cb1..ccca2330eebd 100644
> --- a/fs/resctrl/monitor.c
> +++ b/fs/resctrl/monitor.c
> @@ -984,6 +984,8 @@ int resctrl_mon_resource_init(void)
>                 resctrl_file_fflags_init("available_mbm_cntrs",
>                                          RFTYPE_MON_INFO | RFTYPE_RES_CACHE);
>                 resctrl_file_fflags_init("event_filter", RFTYPE_ASSIGN_CONFIG);
> +               resctrl_file_fflags_init("mbm_assign_on_mkdir", RFTYPE_MON_INFO |
> +                                        RFTYPE_RES_CACHE);
>         }
>
>         return 0;
> diff --git a/fs/resctrl/rdtgroup.c b/fs/resctrl/rdtgroup.c
> index 4889e7556cc7..b7289ce2b3a6 100644
> --- a/fs/resctrl/rdtgroup.c
> +++ b/fs/resctrl/rdtgroup.c
> @@ -1987,6 +1987,42 @@ static ssize_t event_filter_write(struct kernfs_open_file *of, char *buf,
>         return ret ?: nbytes;
>  }
>
> +static int resctrl_mbm_assign_on_mkdir_show(struct kernfs_open_file *of,
> +                                           struct seq_file *s, void *v)
> +{
> +       struct rdt_resource *r = rdt_kn_parent_priv(of->kn);
> +
> +       mutex_lock(&rdtgroup_mutex);
> +       rdt_last_cmd_clear();
> +
> +       seq_printf(s, "%u\n", r->mon.mbm_assign_on_mkdir);
> +
> +       mutex_unlock(&rdtgroup_mutex);
> +
> +       return 0;
> +}
> +
> +static ssize_t resctrl_mbm_assign_on_mkdir_write(struct kernfs_open_file *of,
> +                                                char *buf, size_t nbytes, loff_t off)
> +{
> +       struct rdt_resource *r = rdt_kn_parent_priv(of->kn);
> +       bool value;
> +       int ret;
> +
> +       ret = kstrtobool(buf, &value);
> +       if (ret)
> +               return ret;
> +
> +       mutex_lock(&rdtgroup_mutex);
> +       rdt_last_cmd_clear();
> +
> +       r->mon.mbm_assign_on_mkdir = value;
> +
> +       mutex_unlock(&rdtgroup_mutex);
> +
> +       return 0;

I noticed that "echo 0 > mbm_assign_on_mkdir" never completes. This
should return nbytes.

Thanks,
-Peter