On Wed, Oct 07, 2020 at 07:15:46AM +0200, Greg Kroah-Hartman wrote: > On Tue, Oct 06, 2020 at 08:14:47PM -0700, Ricardo Neri wrote: > > On Tue, Oct 06, 2020 at 09:37:44AM +0200, Greg Kroah-Hartman wrote: > > > On Mon, Oct 05, 2020 at 05:57:36PM -0700, Ricardo Neri wrote: > > > > On Sat, Oct 03, 2020 at 10:53:45AM +0200, Greg Kroah-Hartman wrote: > > > > > On Fri, Oct 02, 2020 at 06:17:42PM -0700, Ricardo Neri wrote: > > > > > > Hybrid CPU topologies combine CPUs of different microarchitectures > > > > > > in the > > > > > > same die. Thus, even though the instruction set is compatible among > > > > > > all > > > > > > CPUs, there may still be differences in features (e.g., some CPUs > > > > > > may > > > > > > have counters that others CPU do not). There may be applications > > > > > > interested in knowing the type of micro-architecture topology of the > > > > > > system to make decisions about process affinity. > > > > > > > > > > > > While the existing sysfs for capacity (/sys/devices/system/cpu/cpuX/ > > > > > > cpu_capacity) may be used to infer the types of micro-architecture > > > > > > of the > > > > > > CPUs in the platform, it may not be entirely accurate. For > > > > > > instance, two > > > > > > subsets of CPUs with different types of micro-architecture may have > > > > > > the > > > > > > same capacity due to power or thermal constraints. > > > > > > > > > > > > Create the new directory /sys/devices/system/cpu/types. Under such > > > > > > directory, create individual subdirectories for each type of CPU > > > > > > micro- > > > > > > architecture. Each subdirectory will have cpulist and cpumap files. > > > > > > This > > > > > > makes it convenient for user space to read all the CPUs of the same > > > > > > type > > > > > > at once without having to inspect each CPU individually. > > > > > > > > > > > > Implement a generic interface using weak functions that > > > > > > architectures can > > > > > > override to indicate a) support for CPU types, b) the CPU type > > > > > > number, and > > > > > > c) a string to identify the CPU vendor and type. > > > > > > > > > > > > For example, an x86 system with one Intel Core and four Intel Atom > > > > > > CPUs > > > > > > would look like this (other architectures have the hooks to use > > > > > > whatever > > > > > > directory naming convention below "types" that meets their needs): > > > > > > > > > > > > user@host:~$: ls /sys/devices/system/cpu/types > > > > > > intel_atom_0 intel_core_0 > > > > > > > > > > > > user@host:~$ ls /sys/devices/system/cpu/types/intel_atom_0 > > > > > > cpulist cpumap > > > > > > > > > > > > user@host:~$ ls /sys/devices/system/cpu/types/intel_core_0 > > > > > > cpulist cpumap > > > > > > > > > > > > user@host:~$ cat /sys/devices/system/cpu/types/intel_atom_0/cpumap > > > > > > 0f > > > > > > > > > > > > user@host:~$ cat /sys/devices/system/cpu/types/intel_atom_0/cpulist > > > > > > 0-3 > > > > > > > > > > > > user@ihost:~$ cat /sys/devices/system/cpu/types/intel_core_0/cpumap > > > > > > 10 > > > > > > > > > > > > user@host:~$ cat /sys/devices/system/cpu/types/intel_core_0/cpulist > > > > > > 4 > > > > > > > > Thank you for the quick and detailed Greg! > > > > > > > > > > > > > > The output of 'tree' sometimes makes it easier to see here, or: > > > > > grep -R . * > > > > > also works well. > > > > > > > > Indeed, this would definitely make it more readable. > > > > > > > > > > > > > > > On non-hybrid systems, the /sys/devices/system/cpu/types directory > > > > > > is not > > > > > > created. Add a hook for this purpose. > > > > > > > > > > Why should these not show up if the system is not "hybrid"? > > > > > > > > My thinking was that on a non-hybrid system, it does not make sense to > > > > create this interface, as all the CPUs will be of the same type. > > > > > > Why not just have this an attribute type in the existing cpuX directory? > > > Why do this have to be a totally separate directory and userspace has to > > > figure out to look in two different spots for the same cpu to determine > > > what it is? > > > > But if the type is located under cpuX, usespace would need to traverse > > all the CPUs and create its own cpu masks. Under the types directory it > > would only need to look once for each type of CPU, IMHO. > > What does a "mask" do? What does userspace care about this?
It would only need to consume the cpu masks that sysfs provides; but it would have to implement the extra step of looking at another directory. > You would have to create it by traversing the directories you are creating > anyway, > so it's not much different, right? True, that is a good point, userspace would still end up traversing diretories anyways. > > > > That feels wasteful, it should be much simpler to use the existing > > > object, right? > > > > > > That way, you also show the "type" of all cpus, no matter if they are > > > "hybrid" or not, again, making userspace deal with things in a much > > > simpler manner. > > > > Indeed, that would be simpler to implement, and perhaps a natural extension > > of the existing interface. > > > > Lastly, legacy and non-hybrid parts will not have a type defined. Thus, > > it may not make sense for them to expose a type in sysfs. > > That's fine, not having a sysfs file if you don't know the type is fine. > Or you can fix that up and show the type of those as well, why wouldn't > you want to? What information should be used for the fixup? On legacy x86 parts, CPUID would not have the leaf that provides this information. Maybe an "unknown" type? > > > > > I thought of this as maybe intel_atcm vs a potential amd_minizen. I > > > > guess arch is sufficient, as there will never be an amd_atom. > > > > > > Even if there is, that can be part of the cpu "type" that you have for > > > your enumerated type, right? > > > > Indeed. The interface I propose lets archs define their own string > > names. > > Arches _should_ define their own names, otherwise who would? Yes, ineed. Thanks and BR, Ricardo