On 6/17/21 4:46 AM, David Gibson wrote:
On Tue, Jun 15, 2021 at 12:35:17PM +0530, Aneesh Kumar K.V wrote:
David Gibson <da...@gibson.dropbear.id.au> writes:
On Tue, Jun 15, 2021 at 11:27:50AM +0530, Aneesh Kumar K.V wrote:
David Gibson <da...@gibson.dropbear.id.au> writes:
On Mon, Jun 14, 2021 at 10:10:03PM +0530, Aneesh Kumar K.V wrote:
FORM2 introduce a concept of secondary domain which is identical to the
conceept of FORM1 primary domain. Use secondary domain as the numa node
when using persistent memory device. For DAX kmem use the logical domain
id introduced in FORM2. This new numa node
Signed-off-by: Aneesh Kumar K.V <aneesh.ku...@linux.ibm.com>
---
arch/powerpc/mm/numa.c | 28 +++++++++++++++++++++++
arch/powerpc/platforms/pseries/papr_scm.c | 26 +++++++++++++--------
arch/powerpc/platforms/pseries/pseries.h | 1 +
3 files changed, 45 insertions(+), 10 deletions(-)
diff --git a/arch/powerpc/mm/numa.c b/arch/powerpc/mm/numa.c
index 86cd2af014f7..b9ac6d02e944 100644
--- a/arch/powerpc/mm/numa.c
+++ b/arch/powerpc/mm/numa.c
@@ -265,6 +265,34 @@ static int associativity_to_nid(const __be32
*associativity)
return nid;
}
+int get_primary_and_secondary_domain(struct device_node *node, int *primary, int *secondary)
+{
+ int secondary_index;
+ const __be32 *associativity;
+
+ if (!numa_enabled) {
+ *primary = NUMA_NO_NODE;
+ *secondary = NUMA_NO_NODE;
+ return 0;
+ }
+
+ associativity = of_get_associativity(node);
+ if (!associativity)
+ return -ENODEV;
+
+ if (of_read_number(associativity, 1) >= primary_domain_index) {
+ *primary = of_read_number(&associativity[primary_domain_index],
1);
+ secondary_index = of_read_number(&distance_ref_points[1], 1);
Secondary ID is always the second reference point, but primary depends
on the length of resources? That seems very weird.
primary_domain_index is distance_ref_point[0]. With Form2 we would find
both primary and secondary domain ID same for all resources other than
persistent memory device. The usage w.r.t. persistent memory is
explained in patch 7.
Right, I misunderstood
With Form2 the primary domainID and secondary domainID are used to identify the
NUMA nodes
the kernel should use when using persistent memory devices.
This seems kind of bogus. With Form1, the primary/secondary ID are a
sort of heirarchy of distance (things with same primary ID are very
close, things with same secondary are kinda-close, etc.). With Form2,
it's referring to their effective node for different purposes.
Using the same terms for different meanings seems unnecessarily
confusing.
They are essentially domainIDs. The interpretation of them are different
between Form1 and Form2. Hence I kept referring to them as primary and
secondary domainID. Any suggestion on what to name them with Form2?
My point is that reusing associativity-reference-points for something
with completely unrelated semantics seems like a very poor choice.
I agree that this reuse can be confusing. I could argue that there is
precedent for that in PAPR - FORM0 puts a different spin on the same
property as well - but there is no need to keep following existing PAPR
practices in new spec (and some might argue it's best not to).
As far as QEMU goes, renaming this property to "numa-associativity-mode"
(just an example) is a quick change to do since we separated FORM1 and FORM2
code over there.
Doing such a rename can also help with the issue of having to describe new
FORM2 semantics using "least significant boundary" or "primary domain" or
any FORM0|FORM1 related terminology.
Thanks,
Daniel
Persistent memory devices
can also be used as regular memory using DAX KMEM driver and primary domainID
indicates
the numa node number OS should use when using these devices as regular memory.
Secondary
domainID is the numa node number that should be used when using this device as
persistent memory.
It's weird to me that you'd want to consider them in different nodes
for those different purposes.
--------------------------------------
| NUMA node0 |
| ProcA -----> MEMA |
| | |
| | |
| -------------------> PMEMB |
| |
---------------------------------------
---------------------------------------
| NUMA node1 |
| |
| ProcB -------> MEMC |
| | |
| -------------------> PMEMD |
| |
| |
---------------------------------------
For a topology like the above application running of ProcA wants to find out
persistent memory mount local to its NUMA node. Hence when using it as
pmem fsdax mount or devdax device we want PMEMB to have associativity
of NUMA node0 and PMEMD to have associativity of NUMA node 1. But when
we want to use it as memory using dax kmem driver, we want both PMEMB
and PMEMD to appear as memory only NUMA node at a distance that is
derived based on the latency of the media.
I'm still not understanding why the latency we care about is different
in the two cases. Can you give an example of when this would result
in different actual node assignments for the two different cases?
