Re: [PATCH v5 10/13] hw/acpi: Generic Port Affinity Structure support

Jonathan Cameron
2024-08-28T16:54:09Z

On Mon, 15 Jul 2024 16:48:41 +0200
Igor Mammedov <imammedo@redhat.com> wrote:

> On Fri, 12 Jul 2024 12:08:14 +0100
> Jonathan Cameron <Jonathan.Cameron@huawei.com> wrote:
>
> > These are very similar to the recently added Generic Initiators
> > but instead of representing an initiator of memory traffic they
> > represent an edge point beyond which may lie either targets or
> > initiators. Here we add these ports such that they may
> > be targets of hmat_lb records to describe the latency and
> > bandwidth from host side initiators to the port. A discoverable
> > mechanism such as UEFI CDAT read from CXL devices and switches
> > is used to discover the remainder of the path, and the OS can build
> > up full latency and bandwidth numbers as need for work and data
> > placement decisions.
> >
> > Acked-by: Markus Armbruster <armbru@redhat.com>
> > Tested-by: "Huang, Ying" <ying.huang@intel.com>
> > Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
>
> ACPI tables generation LGTM
> As for the rest my review is perfunctory mostly.
Hi Igor,

Given I guess we will soon be in the 9.2 cycle, revisiting this
to prepare a v6.

Added missing parameter descriptions for properties in here
and an additional patch for the ones missing for
generic initiators. Another patch fixes the uint32_t fragilty
you pointed out for generic initiators (fixed here as well)

2 things remain, the docs and the question you are asked Markus.

See inline.

>
> > ---
> > v5: Push the definition of TYPE_ACPI_GENERIC_PORT down into the
> > c file (similar to TYPE_ACPI_GENERIC_INITIATOR in earlier patch)
> > ---
> > qapi/qom.json | 34 +++++++++
> > include/hw/acpi/aml-build.h | 4 +
> > include/hw/acpi/pci.h | 2 +-
> > include/hw/pci/pci_bridge.h | 1 +
> > hw/acpi/aml-build.c | 40 ++++++++++
> > hw/acpi/pci.c | 112 +++++++++++++++++++++++++++-
> > hw/arm/virt-acpi-build.c | 2 +-
> > hw/i386/acpi-build.c | 2 +-
> > hw/pci-bridge/pci_expander_bridge.c | 1 -
> > 9 files changed, 193 insertions(+), 5 deletions(-)
> >
> > diff --git a/qapi/qom.json b/qapi/qom.json
> > index 8e75a419c3..b97c031b73 100644
> > --- a/qapi/qom.json
> > +++ b/qapi/qom.json
> > @@ -838,6 +838,38 @@
> > 'data': { 'pci-dev': 'str',
> > 'node': 'uint32' } }
> >
> > +##
> > +# @AcpiGenericPortProperties:
> > +#
> > +# Properties for acpi-generic-port objects.
> > +#
> > +# @pci-bus: QOM path of the PCI bus of the hostbridge associated with
> > +# this SRAT Generic Port Affinity Structure. This is the same as
> > +# the bus parameter for the root ports attached to this host
> > +# bridge. The resulting SRAT Generic Port Affinity Structure will
> > +# refer to the ACPI object in DSDT that represents the host bridge
> > +# (e.g. ACPI0016 for CXL host bridges). See ACPI 6.5 Section
> > +# 5.2.16.7 for more information.
> > +#
>
> > +# @node: Similar to a NUMA node ID, but instead of providing a
> > +# reference point used for defining NUMA distances and access
> > +# characteristics to memory or from an initiator (e.g. CPU), this
> > +# node defines the boundary point between non-discoverable system
> > +# buses which must be described by firmware, and a discoverable
> > +# bus. NUMA distances and access characteristics are defined to
> > +# and from that point. For system software to establish full
> > +# initiator to target characteristics this information must be
> > +# combined with information retrieved from the discoverable part
> > +# of the path. An example would use CDAT (see UEFI.org)
> > +# information read from devices and switches in conjunction with
> > +# link characteristics read from PCIe Configuration space.
>
> you lost me here (even reading this several time doesn't help).
> Perhaps I lack specific domain knowledge, but is there a way to make it
> more comprehensible for layman?

I've had a few passes and clearly still failing :(

Maybe an example is the way to go? Does the following help?
(replacing the 'An example sentence' above).

# For example, a CXL Memory device M is directly
# plugged into a CXL root port P which is part of a
# CXL root bridge B. To calculate latency from a CPU in
# the host to the memory on M, the latency from that CPU
# to the bridge B (and hence port P)* must be added
# to the latency due to the CXL Link between P and M
# (calculated from link status registers) and that from
# the CXL port on device M to the actual memory (read from
# CDAT via a mailbox on the device).
# The CPU to root bridge latency (*) is provided by ACPI HMAT.
# HMAT latency data is indexed with the combination of the
# proximity domain for the CPU and that for the root bridge.
# This node value is the root bridge part of that index pair.

...

> > +static int build_acpi_generic_port(Object *obj, void *opaque)
> > +{
> > + MachineState *ms = MACHINE(qdev_get_machine());
> > + const char *hid = "ACPI0016";
> > + GArray *table_data = opaque;
> > + AcpiGenericPort *gp;
> > + uint32_t uid;
> > + Object *o;
> > +
> > + if (!object_dynamic_cast(obj, TYPE_ACPI_GENERIC_PORT)) {
> > + return 0;
> > + }
> > +
> > + gp = ACPI_GENERIC_PORT(obj);
> > +
> > + if (gp->node >= ms->numa_state->num_nodes) {
>
> > + error_printf("%s: node %d is invalid.\n",
> > + TYPE_ACPI_GENERIC_PORT, gp->node);
> > + exit(1);
>
> not sure,
> maybe use error_fatal instead of using exit(1)?
>
> CCing Markus to check if it's ok.

Markus?

>
>
> > + }
> > +
> > + o = object_resolve_path_type(gp->pci_bus, TYPE_PXB_CXL_BUS, NULL);
> > + if (!o) {
> > + error_printf("%s: device must be a CXL host bridge.\n",
> > + TYPE_ACPI_GENERIC_PORT);
> > + exit(1);
> > + }
> ditto
>