Re: [PATCH v6 00/17] Device tree based NUMA support for Arm

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

Hi Henry,

Thank you for all your work on this series and in general upstreaming
other patches too!

How do we test it? Is there a way to test this series with QEMU and some
special device tree? I am asking because during review it would make
things easier if we could exercise the new code somehow.

I haven't had a chance to review this properly but I noticed that a few
code additions are not protected by CONFIG_NUMA. Maybe they should?

Also given that this is not a small series, I wanted to check with you
if this is a good time to do a full review of the series (in the sense
that you are OK with handling review feedback now) or whether you would
rather have us do the review at another time.

Cheers,

Stefano


On Mon, 20 Nov 2023, Henry Wang wrote:
> The preparation work to support NUMA on Arm has been merged
> and can be found at [1] and [2]. The initial discussions of
> the Arm NUMA support can be found at [3].
> 
> - Background of this series:
> 
> Xen memory allocation and scheduler modules are NUMA aware.
> But actually, on x86 has implemented the architecture APIs
> to support NUMA. Arm was providing a set of fake architecture
> APIs to make it compatible with NUMA awared memory allocation
> and scheduler.
> 
> Arm system was working well as a single node NUMA system with
> these fake APIs, because we didn't have multiple nodes NUMA
> system on Arm. But in recent years, more and more Arm devices
> support multiple nodes NUMA system.
> 
> So now we have a new problem. When Xen is running on these Arm
> devices, Xen still treat them as single node SMP systems. The
> NUMA affinity capability of Xen memory allocation and scheduler
> becomes meaningless. Because they rely on input data that does
> not reflect real NUMA layout.
> 
> Xen still think the access time for all of the memory is the
> same for all CPUs. However, Xen may allocate memory to a VM
> from different NUMA nodes with different access speeds. This
> difference can be amplified in workloads inside VM, causing
> performance instability and timeouts.
> 
> So in this patch series, we implement a set of NUMA API to use
> device tree to describe the NUMA layout. We reuse most of the
> code of x86 NUMA to create and maintain the mapping between
> memory and CPU, create the matrix between any two NUMA nodes.
> Except ACPI and some x86 specified code, we have moved other
> code to common. In next stage, when we implement ACPI based
> NUMA for Arm64, we may move the ACPI NUMA code to common too,
> but in current stage, we keep it as x86 only.
> 
> This patch serires has been tested and booted well on FVP in
> Arm64 mode with NUMA configs in device tree and one HPE x86
> NUMA machine.
> 
> [1] https://lists.xenproject.org/archives/html/xen-devel/2022-06/msg00499.html
> [2] https://lists.xenproject.org/archives/html/xen-devel/2022-11/msg01043.html
> [3] https://lists.xenproject.org/archives/html/xen-devel/2021-09/msg01903.html
> 
> Henry Wang (1):
>   xen/arm: Set correct per-cpu cpu_core_mask
> 
> Wei Chen (16):
>   xen/arm: use NR_MEM_BANKS to override default NR_NODE_MEMBLKS
>   xen/arm: implement helpers to get and update NUMA status
>   xen/arm: implement node distance helpers for Arm
>   xen/arm: use arch_get_ram_range to get memory ranges from bootinfo
>   xen/arm: build NUMA cpu_to_node map in dt_smp_init_cpus
>   xen/arm: Add boot and secondary CPU to NUMA system
>   xen/arm: introduce a helper to parse device tree processor node
>   xen/arm: introduce a helper to parse device tree memory node
>   xen/arm: introduce a helper to parse device tree NUMA distance map
>   xen/arm: unified entry to parse all NUMA data from device tree
>   xen/arm: keep guest still be NUMA unware
>   xen/arm: enable device tree based NUMA in system init
>   xen/arm: implement numa_node_to_arch_nid for device tree NUMA
>   xen/arm: use CONFIG_NUMA to gate node_online_map in smpboot
>   xen/arm: Provide Kconfig options for Arm to enable NUMA
>   docs: update numa command line to support Arm
> 
>  CHANGELOG.md                      |   1 +
>  SUPPORT.md                        |   1 +
>  docs/misc/xen-command-line.pandoc |   2 +-
>  xen/arch/arm/Kconfig              |  11 ++
>  xen/arch/arm/Makefile             |   2 +
>  xen/arch/arm/domain_build.c       |   6 +
>  xen/arch/arm/include/asm/numa.h   |  91 ++++++++-
>  xen/arch/arm/numa-dt.c            | 299 ++++++++++++++++++++++++++++++
>  xen/arch/arm/numa.c               | 184 ++++++++++++++++++
>  xen/arch/arm/setup.c              |  17 ++
>  xen/arch/arm/smpboot.c            |  38 ++++
>  xen/arch/x86/include/asm/numa.h   |   1 -
>  xen/arch/x86/srat.c               |   2 +-
>  xen/include/xen/numa.h            |  10 +
>  14 files changed, 661 insertions(+), 4 deletions(-)
>  create mode 100644 xen/arch/arm/numa-dt.c
>  create mode 100644 xen/arch/arm/numa.c
> 
> -- 
> 2.25.1
>