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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