On Thu, Feb 01, 2024 at 10:57:32AM +0800, Zhao Liu wrote: > Hi Daniel, > > On Wed, Jan 31, 2024 at 10:28:42AM +0000, Daniel P. Berrangé wrote: > > Date: Wed, 31 Jan 2024 10:28:42 +0000 > > From: "Daniel P. Berrangé" <berrange@xxxxxxxxxx> > > Subject: Re: [PATCH v8 00/21] Introduce smp.modules for x86 in QEMU > > > > On Wed, Jan 31, 2024 at 06:13:29PM +0800, Zhao Liu wrote: > > > From: Zhao Liu <zhao1.liu@xxxxxxxxx> > > [snip] > > > > However, after digging deeper into the description and use cases of > > > cluster in the device tree [3], I realized that the essential > > > difference between clusters and modules is that cluster is an extremely > > > abstract concept: > > > * Cluster supports nesting though currently QEMU doesn't support > > > nested cluster topology. However, modules will not support nesting. > > > * Also due to nesting, there is great flexibility in sharing resources > > > on clusters, rather than narrowing cluster down to sharing L2 (and > > > L3 tags) as the lowest topology level that contains cores. > > > * Flexible nesting of cluster allows it to correspond to any level > > > between the x86 package and core. > > > > > > Based on the above considerations, and in order to eliminate the naming > > > confusion caused by the mapping between general cluster and x86 module > > > in v7, we now formally introduce smp.modules as the new topology level. > > > > What is the Linux kernel calling this topology level on x86 ? > > It will be pretty unfortunate if Linux and QEMU end up with > > different names for the same topology level. > > > > Now Intel's engineers in the Linux kernel are starting to use "module" > to refer to this layer of topology [4] to avoid confusion, where > previously the scheduler developers referred to the share L2 hierarchy > collectively as "cluster". > > Looking at it this way, it makes more sense for QEMU to use the > "module" for x86. I was thinking specificially about what Linux calls this topology when exposing it in sysfs and /proc/cpuinfo. AFAICT, it looks like it is called 'clusters' in this context, and so this is the terminology that applications and users are going to expect. I think it would be a bad idea for QEMU to diverge from this and call it modules. With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
