Re: [PATCH v5 07/20] x86/resctrl: Introduce the interface to display monitor mode

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

Hi Reinette,

On 7/12/24 17:06, Reinette Chatre wrote:
> Hi Babu,
> 
> On 7/3/24 2:48 PM, Babu Moger wrote:
>> The ABMC feature provides an option to the user to assign a hardware
>> counter to an RMID and monitor the bandwidth as long as it is assigned.
>> ABMC mode is enabled by default when supported. System can be one mode
>> at a time (Legacy monitor mode or ABMC mode).
>>
>> Provide an interface to display the monitor mode on the system.
>>      $cat /sys/fs/resctrl/info/L3_MON/mbm_mode
>>      [abmc]
>>      legacy
> 
> <insert snippet about what happens when user switches from one mode
> to another>

Sure.

> 
>>
>> Signed-off-by: Babu Moger <babu.moger@amd.com>
>> ---
>> v5: Changed interface name to mbm_mode.
>>      It will be always available even if ABMC feature is not supported.
>>      Added description in resctrl.rst about ABMC mode.
>>      Fixed display abmc and legacy consistantly.
>>
>> v4: Fixed the checks for legacy and abmc mode. Default it ABMC.
>>
>> v3: New patch to display ABMC capability.
>> ---
>>   Documentation/arch/x86/resctrl.rst     | 30 ++++++++++++++++++++++++++
>>   arch/x86/kernel/cpu/resctrl/monitor.c  |  2 ++
>>   arch/x86/kernel/cpu/resctrl/rdtgroup.c | 26 ++++++++++++++++++++++
>>   3 files changed, 58 insertions(+)
>>
>> diff --git a/Documentation/arch/x86/resctrl.rst
>> b/Documentation/arch/x86/resctrl.rst
>> index 30586728a4cd..108e494fd7cc 100644
>> --- a/Documentation/arch/x86/resctrl.rst
>> +++ b/Documentation/arch/x86/resctrl.rst
>> @@ -257,6 +257,36 @@ with the following files:
>>           # cat /sys/fs/resctrl/info/L3_MON/mbm_local_bytes_config
>>           0=0x30;1=0x30;3=0x15;4=0x15
>>   +"mbm_mode":
>> +    Reports the list of assignable monitoring features supported. The
>> +    enclosed brackets indicate which feature is enabled.
>> +    ::
>> +
>> +      cat /sys/fs/resctrl/info/L3_MON/mbm_mode
>> +      [abmc]
>> +      legacy
>> +
> 
> "mbm_cntr" mode can be documented here with the details on how AMD's ABMC is
> one example of how it may be implemented on a system.

Will display as "mbm_cntr_assignable".

Yes. Will add details specific about AMD's ABMC.

> 
>> +    The bandwidth monitoring feature on AMD system only guarantees that
>> +    RMIDs currently assigned to a processor will be tracked by hardware.
>> +    The counters of any other RMIDs which are no longer being tracked
>> +    will be reset to zero. The MBM event counters return "Unavailable"
>> +    for the RMIDs that are not tracked by hardware. So, there can be
>> +    only limited number of groups that can give guaranteed monitoring
>> +    numbers. With ever changing configurations there is no way to
>> +    definitely know which of these groups are being tracked for certain
>> +    point of time. Users do not have the option to monitor a group or
>> +    set of groups for certain period of time without worrying about
>> +    RMID being reset in between.
>> +
>> +    The ABMC feature provides an option to the user to assign a
>> +    hardware counter to an RMID and monitor the bandwidth as long as
>> +    it is assigned. The assigned RMID will be tracked by the hardware
>> +    until the user unassigns it manually. There is no need to worry
>> +    about counters being reset during this period.
>> +
>> +    Without ABMC enabled, monitoring will work in "legacy" mode
>> +    without assignment option.
> 
> Let "legacy" be a distinct mode, instead of an alternative to ABMC.

Will add as another mode.

> 
>> +
>>   "max_threshold_occupancy":
>>           Read/write file provides the largest value (in
>>           bytes) at which a previously used LLC_occupancy
>> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c
>> b/arch/x86/kernel/cpu/resctrl/monitor.c
>> index 12793762ca24..6c4cb36b4b50 100644
>> --- a/arch/x86/kernel/cpu/resctrl/monitor.c
>> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c
>> @@ -1245,6 +1245,8 @@ int __init rdt_get_mon_l3_config(struct
>> rdt_resource *r)
>>           }
>>       }
>>   +    resctrl_file_fflags_init("mbm_mode", RFTYPE_MON_INFO);
>> +
> 
> Is this special flag assignment necessary? With file always visible I
> think it
> can just be initialized in res_common_files below with the flag already
> assigned?

Yes. We can do that.

> 
>>       l3_mon_evt_init(r);
>>         r->mon_capable = true;
>> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> index 471fc0dbd7c3..3988d7b86817 100644
>> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
>> @@ -845,6 +845,26 @@ static int rdtgroup_rmid_show(struct
>> kernfs_open_file *of,
>>       return ret;
>>   }
>>   +static int rdtgroup_mbm_mode_show(struct kernfs_open_file *of,
>> +                  struct seq_file *s, void *v)
>> +{
>> +    struct rdt_resource *r = of->kn->parent->priv;
>> +
>> +    if (r->mon.abmc_capable) {
>> +        if (resctrl_arch_get_abmc_enabled()) {
>> +            seq_puts(s, "[abmc]\n");
>> +            seq_puts(s, "legacy\n");
>> +        } else {
>> +            seq_puts(s, "abmc\n");
>> +            seq_puts(s, "[legacy]\n");
>> +        }
>> +    } else {
>> +        seq_puts(s, "[legacy]\n");
>> +    }
>> +
>> +    return 0;
>> +}
>> +
>>   #ifdef CONFIG_PROC_CPU_RESCTRL
>>     /*
>> @@ -1901,6 +1921,12 @@ static struct rftype res_common_files[] = {
>>           .seq_show    = mbm_local_bytes_config_show,
>>           .write        = mbm_local_bytes_config_write,
>>       },
>> +    {
>> +        .name        = "mbm_mode",
>> +        .mode        = 0444,
>> +        .kf_ops        = &rdtgroup_kf_single_ops,
>> +        .seq_show    = rdtgroup_mbm_mode_show,
>> +    },
>>       {
>>           .name        = "cpus",
>>           .mode        = 0644,
> 
> Reinette
> 

-- 
Thanks
Babu Moger