On Sat, Oct 19, 2019 at 02:45:43PM +0800, Yunsheng Lin wrote: > As the disscusion in [1]: We need to justify this patch right here in the commit log, not with a pointer to a 50+ message email thread. > A PCI device really _MUST_ have a node assigned. No, it's not really essential. It's *nice* if we know the node closest to a PCI device, but the system should function correctly even if we don't. The only problem is that it will be slower. I think the underlying problem you're addressing is that: - NUMA_NO_NODE == -1, - dev_to_node(dev) may return NUMA_NO_NODE, - kmalloc(dev) relies on cpumask_of_node(dev_to_node(dev)), and - cpumask_of_node(NUMA_NO_NODE) makes an invalid array reference For example, on arm64, mips loongson, s390, and x86, cpumask_of_node(node) returns "node_to_cpumask_map[node]", and -1 is an invalid array index. That problem can't be solved by emitting a warning, of course. I assume some variation of your "numa: make node_to_cpumask_map() NUMA_NO_NODE aware" patch [a] will solve that problem. [a] https://lore.kernel.org/linux-mips/1568535656-158979-1-git-send-email-linyunsheng@xxxxxxxxxx/T/#u It is probably a good idea to emit a warning about the performance issue. When I run your patch on qemu, I see this: ACPI: PCI Root Bridge [PCI0] (domain 0000 [bus 00-ff]) acpi PNP0A08:00: _OSC: OS supports [ExtendedConfig ASPM ClockPM Segments MSI HPX-Type3] acpi PNP0A08:00: _OSC: platform does not support [LTR] acpi PNP0A08:00: _OSC: OS now controls [PME AER PCIeCapability] PCI host bridge to bus 0000:00 pci_bus 0000:00: root bus resource [io 0x0000-0x0cf7 window] pci_bus 0000:00: root bus resource [io 0x0d00-0xffff window] pci_bus 0000:00: root bus resource [mem 0x000a0000-0x000bffff window] pci_bus 0000:00: root bus resource [mem 0xc0000000-0xfebfffff window] pci_bus 0000:00: root bus resource [mem 0x100000000-0x8ffffffff window] pci_bus 0000:00: root bus resource [bus 00-ff] pci0000:00: [Firmware Bug]: No node assigned on NUMA capable HW by BIOS. Please contact your vendor for updates. I didn't debug it to see what's wrong with the " pci0000:00" string. Ideally it would be connected with "acpi PNP0A08:00" since that's the place where BIOS would make a fix but I suppose "pci_bus 0000:00" would be adequate. > It is possible to > have a PCI bridge shared between two nodes, such that the PCI > devices have equidistance. But the moment you scale this out, you > either get devices that are 'local' to a package while having > multiple packages, or if you maintain a single bridge in a big > system, things become so slow it all doesn't matter anyway. > Assigning a node (one of the shared) is, in the generic ase of > multiple packages, the better solution over assigning all nodes. > > As pci_device_add() will assign the pci device' node according to > the bus the device is on, which is decided by pcibus_to_node(). > Currently different arch may implement the pcibus_to_node() based > on bus->sysdata or bus device' node, which has the same node as > the bridge device. > > And for devices behind another bridge case, the child bus device > is setup with proper parent bus device and inherit its parent' > sysdata in pci_alloc_child_bus(), so the pcie device under the > child bus should have the same node as the parent bridge when > device_add() is called, which will set the node to its parent's > node when the child device' node is NUMA_NO_NODE. > > So this patch only warns about the case when a host bridge device > is registered with a node of NO_NODE in pci_register_host_bridge(). > And it only warns about that when there are more than one numa > nodes in the system. > [1] https://lore.kernel.org/lkml/1568724534-146242-1-git-send-email-linyunsheng@xxxxxxxxxx/ > > Signed-off-by: Yunsheng Lin <linyunsheng@xxxxxxxxxx> > --- > drivers/pci/probe.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c > index 3d5271a..22be96a 100644 > --- a/drivers/pci/probe.c > +++ b/drivers/pci/probe.c > @@ -927,6 +927,9 @@ static int pci_register_host_bridge(struct pci_host_bridge *bridge) > list_add_tail(&bus->node, &pci_root_buses); > up_write(&pci_bus_sem); > > + if (nr_node_ids > 1 && dev_to_node(bus->bridge) == NUMA_NO_NODE) > + dev_err(bus->bridge, FW_BUG "No node assigned on NUMA capable HW by BIOS. Please contact your vendor for updates.\n"); > + > return 0; > > unregister:
