Re: [PATCH 0/9] Add CPU-type to topology

[Brice Goglin]

Le 19/06/2024 à 12:34, srinivas pandruvada a écrit :
> On Tue, 2024-06-18 at 18:53 -0700, Pawan Gupta wrote:
> > On Tue, Jun 18, 2024 at 02:49:10PM +0200, Brice Goglin wrote:
> > > Le 17/06/2024 à 11:11, Pawan Gupta a écrit :
> > > > Hi,
> > > >
> > > > This series adds support for CPU-type (CPUID.1A.EAX[31-24] on
> > > > Intel) to
> > > > differentiate between hybrid variants P+E, P-only, E-only that
> > > > share the
> > > > same Family/Model/Stepping. One of the use case for CPU-type is
> > > > the
> > > > affected CPU table for CPU vulnerabilities, which can now use the
> > > > CPU-type
> > > > to filter the unaffected variants.
> > > >
> > > > * Patch 1 adds cpu-type to CPU topology structure and introduces
> > > >     topology_cpu_type() to get the CPU-type.
> > > >
> > > > * Patch 2-4 replaces usages of get_this_hybrid_cpu_type() with
> > > >     topology_cpu_type().
> > > >
> > > > * Patch 5-7 Updates CPU-matching infrastructure to use CPU-type.
> > > >
> > > > * Patch 8 cleans up the affected CPU list.
> > > >
> > > > * Patch 9 uses the CPU-type to exclude P-only parts from the RFDS
> > > > affected
> > > >     list.
> > >
> > > Hello
> > >
> > > Is there still a plan to expose this info in sysfs?
> > Sure, if it helps userspace.
> >
> > > Userspace currently uses frequencies to guess which cores are E or
> > > P.
> > > Intel sent some patches several years ago [1], but they got
> > > abandoned
> > > nowhere as far as I know. There was also some discussion about
> > > using a
> > > "capacity" field like ARM does, but IIRC Intel didn't like the idea
> > > in
> > > the end.
> > There can be many ways to expose this information in sysfs. Like this
> > ...
> >
> > > [1] https://lkml.org/lkml/2020/10/2/1208
> > ... exposes /sys/devices/system/cpu/types which, in hybrid parts,
> > creates a
> > subdirectory for each type of CPU. Each subdirectory contains a CPU
> > list
> > and a CPU map that user space can query.
> >
> > The other way is to expose the CPU-type in a file:
> >
> >          /sys/devices/system/cpu/cpuN/type
> >
> > that could return the CPU-type of the CPU N. Is there a preference?
> But you still have to look at frequency or caches as there are Low
> power E-cores which will have same type but different capabilities.


Good point. From this patch series, I understand that the current kernel 
side doesn't care about these different E-cores. However it might be 
good to expose them as different cpu-types (or better name) to userspace ?

Something like type 0 = P-core, 1 = normal E-core, 2 = low power E-core ?

Brice