Messages in this thread | | | Date | Mon, 18 Mar 2024 09:03:19 +0800 | From | Feng Tang <> | Subject | Re: [PATCH] x86/tsc: Use topology_max_packages() to get package number |
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On Fri, Mar 15, 2024 at 09:51:32PM +0100, Thomas Gleixner wrote: > On Fri, Mar 15 2024 at 10:58, Dave Hansen wrote: > > On 3/15/24 04:26, Feng Tang wrote: > >> /* > >> * Today neither Intel nor AMD support heterogeneous systems so > >> * extrapolate the boot cpu's data to all packages. > >> */ > >> ncpus = cpu_data(0).booted_cores * topology_max_smt_threads(); > >> __max_logical_packages = DIV_ROUND_UP(total_cpus, ncpus); > > > > Because Intel obviously has heterogeneous systems today. > > Hybrid is a per package property. > > But neither Intel nor AMD support populating multi socket systems with > random packages, where socket 0 has less cores than socket 1 or socket 0 > is hybrid and socket 1 is not.
Before posting the patch, I run the latest upstream kernel with your topology refactoring patchset on one AlderLake and one MetorLake box, and they both show the number of package is 1.
> > > So I'll buy that removing 'nr_online_nodes' takes NUMA out of the > > picture (which is good), but I want to hear more about why > > topology_max_packages() and '4' are the right things to be checking. > > > > I suspect the real reason '4' was picked was to give the calculation > > some wiggle room because it's not actually all that precise. > > IIRC the TSC is only guaranteed to be synchronized up to 4 sockets, but > my memory might be wrong as usual.
Yes. I did try to increase the bar to '8' with a patch, and at that time Peter Zijlstra mentioned there was real issue with TSC found on some old 8 sockets machine.
Thanks, Feng
> > Thanks, > > tglx
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