Re: [External Mail] [RFC PATCH] mm/mempolicy: Weighted interleave auto-tuning

Gregory Price
2024-12-13T16:28:22Z

On Fri, Dec 13, 2024 at 03:19:20PM +0900, Hyeonggon Yoo wrote:
> On 2024-12-11 06:54 AM, Joshua Hahn wrote:
> > This patch introduces an auto-configuration for the interleave weights
> > that aims to balance the two goals of setting node weights to be
> > proportional to their bandwidths and keeping the weight values low.
> > This balance is controlled by a value max_node_weight, which defines the
> > maximum weight a single node can take.
>
> Hi Joshua,
>
> I am wondering how this is going to work for host memory + CXL memory
> interleaving. I guess by "the ACPI table" you mean the ACPI HMAT or CXL
> CDAT, both of which does not provide the bandwidth of host memory.

Then your BIOS vendor needs to fix their ACPI table generation, because
HMAT can absolutely contain that information.

[078h 0120 2] Structure Type : 0001 [System Locality Latency and Bandwidth Information]
[07Ah 0122 2] Reserved : 0000
[07Ch 0124 4] Length : 00000030
[080h 0128 1] Flags (decoded below) : 00
Memory Hierarchy : 0
Use Minimum Transfer Size : 0
Non-sequential Transfers : 0
[081h 0129 1] Data Type : 00
[082h 0130 1] Minimum Transfer Size : 00
[083h 0131 1] Reserved1 : 00
[084h 0132 4] Initiator Proximity Domains # : 00000001
[088h 0136 4] Target Proximity Domains # : 00000002
[08Ch 0140 4] Reserved2 : 00000000
[090h 0144 8] Entry Base Unit : 00000000000003E8
[098h 0152 4] Initiator Proximity Domain List : 00000000
[09Ch 0156 4] Target Proximity Domain List : 00000000
[0A0h 0160 4] Target Proximity Domain List : 00000001
[0A4h 0164 2] Entry : 006E
[0A6h 0166 2] Entry : 01FE

[0A8h 0168 2] Structure Type : 0001 [System Locality Latency and Bandwidth Information]
[0AAh 0170 2] Reserved : 0000
[0ACh 0172 4] Length : 00000030
[0B0h 0176 1] Flags (decoded below) : 00
Memory Hierarchy : 0
Use Minimum Transfer Size : 0
Non-sequential Transfers : 0
[0B1h 0177 1] Data Type : 03
[0B2h 0178 1] Minimum Transfer Size : 00
[0B3h 0179 1] Reserved1 : 00
[0B4h 0180 4] Initiator Proximity Domains # : 00000001
[0B8h 0184 4] Target Proximity Domains # : 00000002
[0BCh 0188 4] Reserved2 : 00000000
[0C0h 0192 8] Entry Base Unit : 0000000000000064
[0C8h 0200 4] Initiator Proximity Domain List : 00000000
[0CCh 0204 4] Target Proximity Domain List : 00000000
[0D0h 0208 4] Target Proximity Domain List : 00000001
[0D4h 0212 2] Entry : 1200
[0D6h 0214 2] Entry : 0064

Obviously if information is missing, then manual is the only way forward.

> > + The maximum interleave weight for a memory node. When it is
> > + updated, any previous changes to interleave weights (i.e. via
> > + the nodeN sysfs interfaces) are ignored, and new weights are
> > + calculated using ACPI-reported bandwidths and scaled.
> > +
>
> At first this paragraph sounded like "previously stored weights are
> discarded after setting max_node_weight", but I think you mean
> "User can override the default values, but defaults values are calculated
> regardless of the values set by the user". Right?
>

Agree that these comments need clarification, we'll workshop it.

~Gregory