[PATCH] arm64: PCI: Remove node-local allocations when initialising host controller

[lorenzo.pieralisi@arm.com (Lorenzo Pieralisi)]

On Wed, Aug 01, 2018 at 02:38:51PM -0500, Jeremy Linton wrote:
> Hi,
> 
> +CC Jiang Lui

Jiang Liu does not work on the kernel anymore so we won't know
anytime soon the reasoning behind commit 965cd0e4a5e5

> On 08/01/2018 12:31 PM, Punit Agrawal wrote:
> >Memory for host controller data structures is allocated local to the
> >node to which the controller is associated with. This has been the
> >behaviour since support for ACPI was added in
> >commit 0cb0786bac15 ("ARM64: PCI: Support ACPI-based PCI host controller").
> 
> Which was apparently influenced by:
> 
> 965cd0e4a5e5 x86, PCI, ACPI: Use kmalloc_node() to optimize for performance
> 
> Was there an actual use-case behind that change?
> 
> I think this fixes the immediate boot problem, but if there is any
> perf advantage it seems wise to keep it... Particularly since x86
> seems to be doing the node sanitation in pci_acpi_root_get_node().

I am struggling to see the perf advantage of allocating a struct
that the PCI controller will never read/write from a NUMA node that
is local to the PCI controller, happy to be corrected if there is
a sound rationale behind that.

Lorenzo

> 
> 
> 
> >
> >Drop the node local allocation as there is no benefit from doing so -
> >the usage of these structures is independent from where the controller
> >is located. It also causes problem during probe if the associated numa
> >node hasn't been initialised due to booting with restricted cpus via
> >kernel command line or where the node doesn't have cpus or memory
> >associated with it.
> >
> >Signed-off-by: Punit Agrawal <punit.agrawal@arm.com>
> >Cc: Catalin Marinas <catalin.marinas@arm.com>
> >Cc: Will Deacon <will.deacon@arm.com>
> >Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
> >---
> >Hi,
> >
> >This came up in the context of investigating the boot issues reported
> >due to restricted cpus or buggy firmware. Part of the problem is fixed
> >by Lorenzo's rework of NUMA initialisation[0].
> >
> >But there also doesn't seem to be any justification for using
> >node-local allocation to begin with.
> >
> >Thanks,
> >Punit
> >
> >[0] https://patchwork.kernel.org/patch/10486001/
> >
> >  arch/arm64/kernel/pci.c | 5 ++---
> >  1 file changed, 2 insertions(+), 3 deletions(-)
> >
> >diff --git a/arch/arm64/kernel/pci.c b/arch/arm64/kernel/pci.c
> >index 0e2ea1c78542..bb85e2f4603f 100644
> >--- a/arch/arm64/kernel/pci.c
> >+++ b/arch/arm64/kernel/pci.c
> >@@ -165,16 +165,15 @@ static void pci_acpi_generic_release_info(struct acpi_pci_root_info *ci)
> >  /* Interface called from ACPI code to setup PCI host controller */
> >  struct pci_bus *pci_acpi_scan_root(struct acpi_pci_root *root)
> >  {
> >-	int node = acpi_get_node(root->device->handle);
> >  	struct acpi_pci_generic_root_info *ri;
> >  	struct pci_bus *bus, *child;
> >  	struct acpi_pci_root_ops *root_ops;
> >-	ri = kzalloc_node(sizeof(*ri), GFP_KERNEL, node);
> >+	ri = kzalloc(sizeof(*ri), GFP_KERNEL);
> >  	if (!ri)
> >  		return NULL;
> >-	root_ops = kzalloc_node(sizeof(*root_ops), GFP_KERNEL, node);
> >+	root_ops = kzalloc(sizeof(*root_ops), GFP_KERNEL);
> >  	if (!root_ops) {
> >  		kfree(ri);
> >  		return NULL;
> >
>