Re: [PATCH 2/2] xen: credit2: limit the max number of CPUs in a runqueue

[Jan Beulich <jbeulich@suse.com>]

On 28.05.2020 16:55, Dario Faggioli wrote:
> On Wed, 2020-05-27 at 08:17 +0200, Jan Beulich wrote:
>> On 27.05.2020 00:00, Dario Faggioli wrote:
>>> Just in case, is there a
>>> way to identify them easily, like with a mask or something, in the
>>> code
>>> already?
>>
>> cpu_sibling_mask still gets used for both, so there's no mask
>> to use. As per set_cpu_sibling_map() you can look at
>> cpu_data[].compute_unit_id to tell, but that's of course x86-
>> specific (as is the entire compute unit concept).
>>
> Right. And thanks for the pointers.
> 
> But then, what I am understanding by having a look there is that I
> indeed can use (again, appropriately wrapped) x86_num_siblings, for
> telling, in this function, whether a CPU has any, and if yes how many,
> HT (Intel) or CU (AMD) siblings in total, although some of them may
> currently be offline.
> 
> Which means I will be treating HTs and CUs the same which, thinking
> more about it (and thinking actually to CUs, rather than to any cache
> sharing relationship), does make sense for this feature.
> 
> Does this make sense, or am I missing or misinterpreting anything?

Well, it effectively answers the question I had raised: "What about HT
vs AMD Fam15's CUs? Do you want both to be treated the same here?"

Jan