Re: [RFC] memory tiering: use small chunk size and more tiers

[Huang, Ying]

Bharata B Rao <bharata@xxxxxxx> writes:

> On 10/28/2022 11:16 AM, Huang, Ying wrote:
>> If my understanding were correct, you think the latency / bandwidth of
>> these NUMA nodes will near each other, but may be different.
>> 
>> Even if the latency / bandwidth of these NUMA nodes isn't exactly same,
>> we should deal with that in memory types instead of memory tiers.
>> There's only one abstract distance for each memory type.
>> 
>> So, I still believe we will not have many memory tiers with my proposal.
>> 
>> I don't care too much about the exact number, but want to discuss some
>> general design choice,
>> 
>> a) Avoid to group multiple memory types into one memory tier by default
>>    at most times.
>
> Do you expect the abstract distances of two different types to be
> close enough in real life (like you showed in your example with
> CXL - 5000 and PMEM - 5100) that they will get assigned into same tier
> most times?
>
> Are you foreseeing that abstract distance that get mapped by sources
> like HMAT would run into this issue?

Only if we set abstract distance chunk size large.  So, I think that
it's better to set chunk size as small as possible to avoid potential
issue.  What is the downside to set the chunk size small?

Best Regards,
Huang, Ying