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

["Moger, Babu" <babu.moger@amd.com>]

Hi Peter,

On 7/15/25 08:53, Peter Newman wrote:
> 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.
> 

Agree. Thanks for pointing it out.
-- 
Thanks
Babu Moger