Re: [PATCH v8 08/25] x86/resctrl: Introduce interface to display number of monitoring counters

[Moger, Babu]

Hi Tony,

On 10/10/24 13:57, Luck, Tony wrote:
>>> Why have this complexity in mbm_assign_control syntax?
>>
>> Lets take an example:
>> $ cat /sys/fs/resctrl/info/L3_MON/num_mbm_cntrs
>> Total 32
>> Available 30
>>
>> # cat /sys/fs/resctrl/info/L3_MON/mbm_assign_control
>> //0=tl;1=tl;
>>
>> Here default group has taken two counters.
>>
>> # cat /sys/fs/resctrl/info/L3_MON/mbm_assign_control
>> //0=_;1=tl;
>>
>> Here default group has two counters.
>> Domain 0 does not have counters applied. So, you wont be able to read the
>> MBM values for domain 0.
>> Domain 1 has both the counters applied.
> 
> Is there some benefit from doing this? You are still using the same
> number of counters. You now can't read them from domain 0.
> 
> You said the counters are system-wide. Does that mean that in 
> this case:

Counter are system wide. We also keep track if the counters is applied to
specific domain or not. We have two bitmaps to keep track of this.

There is a cost to applying counter to the domain(IPI needs to be sent to
the domain).


> 
> # cat /sys/fs/resctrl/info/L3_MON/mbm_assign_control
> //0=tl;1=tl;
> 
> there aren't separate counts from each of domain 0 and domain 1.

Yes. There is. Each domain has its own count. I am not sure about your config.

# cat /sys/fs/resctrl/info/L3_MON/mbm_assign_control
 //0=_;1=tl;

# grep . /sys/fs/resctrl/mon_data/*/*total*
/sys/fs/resctrl/mon_data/mon_L3_00/mbm_total_bytes:Unassigned
/sys/fs/resctrl/mon_data/mon_L3_01/mbm_total_bytes:22976

> I.e. if I read both I'd see the same value (sum of traffic on both domains):
> 
> $ grep . /sys/fs/resctrl/mon_data/*/*total*
> /sys/fs/resctrl /mon_data/mon_L3_00/mbm_total_bytes:260039467008
> /sys/fs/resctrl /mon_data/mon_L3_01/mbm_total_bytes:260039467008
> 
> -Tony

-- 
Thanks
Babu Moger