Messages in this thread | | | Date | Mon, 5 Oct 2020 17:24:04 -0700 | From | Ricardo Neri <> | Subject | Re: [PATCH 0/3] x86: Add initial support to discover Intel hybrid CPUs |
| |
On Sat, Oct 03, 2020 at 11:04:29AM +0200, Borislav Petkov wrote: > On Fri, Oct 02, 2020 at 07:17:30PM -0700, Luck, Tony wrote: > > On Sat, Oct 03, 2020 at 03:39:29AM +0200, Thomas Gleixner wrote: > > > On Fri, Oct 02 2020 at 13:19, Ricardo Neri wrote: > > > > Add support to discover and enumerate CPUs in Intel hybrid parts. A hybrid > > > > part has CPUs with more than one type of micro-architecture. Thus, certain > > > > features may only be present in a specific CPU type. > > > > > > > > It is useful to know the type of CPUs present in a system. For instance, > > > > perf may need to handle CPUs differently depending on the type of micro- > > > > architecture. Decoding machine check error logs may need the additional > > > > micro-architecture type information, so include that in the log. > > > > > > 'It is useful' as justification just makes me barf. > > > > This isn't "hetero" ... all of the cores are architecturally the same. > > But it says above "A hybrid part has CPUs with more than one type of > micro-architecture." > > So which is it?
Yes, even though they have different micro-architectures, all instructions and features will be the same across CPUs.
> > > If CPUID says that some feature is supported, then it will be supported > > on all of the cores. > > Ok. > > > There might be some model specific performance counter events that only > > apply to some cores. > > That sounds like the perf counter scheduling code would have to pay > attention to what is supported. I think we have some functionality for > that due to some AMD parts but I'd prefer if Peter comments here. > > > Or a machine check error code that is logged in the model specific > > MSCOD field of IA32_MCi_STATUS. But any and all code can run on any > > core. > > As long as that is consumed only by userspace I guess that's ok. The > moment someone starts to want to differentiate on what kind of CPU > kernel code runs and acts accordingly, then it becomes ugly so we better > hash it out upfront.
We are not planning to implement changes as such.
Thanks and BR, Ricardo
| |