Re: [RFC PATCH 0/6] Introduce cluster cpu topology support

[wangyanan (Y)]

Hi Paolo,

On 2021/3/31 18:00, Paolo Bonzini wrote:
> On 31/03/21 11:53, Yanan Wang wrote:
> > A cluster means a group of cores that share some resources (e.g. cache)
> > among them under the LLC. For example, ARM64 server chip Kunpeng 920 has
> > 6 or 8 clusters in each NUMA, and each cluster has 4 cores. All clusters
> > share L3 cache data while cores within each cluster share the L2 cache.
>
> Is this different from what we already have with "-smp dies"?
As far as I know, yes. I think they are two architecture concepts of 
different levels.
A cpu socket/package can consist of multiple dies, and each die can 
consist of
multiple clusters, which means dies are parent for clusters. And this 
kind of cpu
hierarchy structure is normal in ARM64 platform.

Still take above ARM64 server chip Kunpeng 920 as an example, there 
totally are
2 sockets, 2 dies in each socket, 6 or 8 clusters in each die, and 4 
cores in each
cluster. Since it also supports NUMA architecture, then each NUMA actually
represents one die.

Although there is already "-smp dies=*" command line parameter for PC 
Machines,
a cluster level can be added for x86 architecture if meaningful and 
there will be more
work to do in qemu to make use of it. And I am sure that ARM needs this 
level.

If there is something wrong above, please correct me, thanks!

Thanks,
Yanan
> Paolo
>
> .