Messages in this thread | | | Subject | Re: [PATCH v3 6/7] arm64: topology: Enable ACPI/PPTT based CPU topology. | From | Jeremy Linton <> | Date | Fri, 20 Oct 2017 11:14:31 -0500 |
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Hi,
On 10/20/2017 04:14 AM, Lorenzo Pieralisi wrote: > On Thu, Oct 19, 2017 at 11:13:27AM -0500, Jeremy Linton wrote: >> On 10/19/2017 10:56 AM, Lorenzo Pieralisi wrote: >>> On Thu, Oct 12, 2017 at 02:48:55PM -0500, Jeremy Linton wrote: >>>> Propagate the topology information from the PPTT tree to the >>>> cpu_topology array. We can get the thread id, core_id and >>>> cluster_id by assuming certain levels of the PPTT tree correspond >>>> to those concepts. The package_id is flagged in the tree and can be >>>> found by passing an arbitrary large level to setup_acpi_cpu_topology() >>>> which terminates its search when it finds an ACPI node flagged >>>> as the physical package. If the tree doesn't contain enough >>>> levels to represent all of thread/core/cod/package then the package >>>> id will be used for the missing levels. >>>> >>>> Since server/ACPI machines are more likely to be multisocket and NUMA, >>> >>> I think this stuff is vague enough already so to start with I would drop >>> patch 4 and 5 and stop assuming what machines are more likely to ship >>> with ACPI than DT. >>> >>> I am just saying, for the umpteenth time, that these levels have no >>> architectural meaning _whatsoever_, level is a hierarchy concept >>> with no architectural meaning attached. >> >> ? >> >> Did anyone say anything about that? No, I think the only thing being >> guaranteed here is that the kernel's physical_id maps to an ACPI >> defined socket. Which seems to be the mindset of pretty much the >> entire !arm64 community meaning they are optimizing their software >> and the kernel with that concept in mind. >> >> Are you denying the existence of non-uniformity between threads >> running on different physical sockets? > > No, I have not explained my POV clearly, apologies. > > AFAIK, the kernel currently deals with 2 (3 - if SMT) topology layers. > > 1) thread > 2) core > 3) package > > What I wanted to say is, that, to simplify this series, you do not need > to introduce the COD topology level, since it is just another arbitrary > topology level (ie there is no way you can pinpoint which level > corresponds to COD with PPTT - or DT for the sake of this discussion) > that would not be used in the kernel (apart from big.LITTLE cpufreq > driver and PSCI checker whose usage of topology_physical_package_id() is > questionable anyway).
Oh! But, i'm at a loss as to what to do with those two users if I set the node which has the physical socket flag set, as the "cluster_id" in the topology.
Granted, this being ACPI I don't expect the cpufreq driver to be active (given CPPC) and the psci checker might be ignored? Even so, its a bit of a misnomer what is actually happening. Are we good with this?
> > PPTT allows you to define what level corresponds to a package, use > it to initialize the package topology level (that on ARM internal > variables we call cluster) and be done with it. > > I do not think that adding another topology level improves anything as > far as ACPI topology detection is concerned, you are not able to use it > in the scheduler or from userspace to group CPUs anyway.
Correct, and AFAIK after having poked a bit at the scheduler its sort of redundant as the generic cache sharing levels are more useful anyway.
> > Does this answer your question ? Yes, other than what to do with the two drivers.
> > Thanks, > Lorenzo >
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