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Commit 63692df1 authored by Prarit Bhargava's avatar Prarit Bhargava Committed by Bjorn Helgaas
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PCI: Allow numa_node override via sysfs 



NUMA systems with ACPI normally describe the physical topology via _PXM
methods.  But many BIOSes don't implement _PXM, which leaves the kernel
with no way to discover the device topology, which reduces performance
because we can't put memory and processes close to the device.

The NUMA node of a PCI device is already exported in the sysfs "numa_node"
file.  Make that file writable so users can workaround the lack of _PXM
methods in the BIOS.  For example:

  echo 3 > /sys/devices/pci0000:ff/0000:03:1f.3/numa_node

sets the node for PCI device 0000:03:1f.3.

Writing the file emits a FW_BUG warning to encourage users to request
firmware updates.  It also taints the kernel with TAINT_FIRMWARE_WORKAROUND
because overriding the node incorrectly can cause performance issues.

[bhelgaas: changelog, documentation text]
Signed-off-by: default avatarPrarit Bhargava <prarit@redhat.com>
Signed-off-by: default avatarBjorn Helgaas <bhelgaas@google.com>
CC: Myron Stowe <mstowe@redhat.com>
CC: Alexander Ducyk <alexander.h.duyck@redhat.com>
CC: Jiang Liu <jiang.liu@linux.intel.com>
parent f114040e

Documentation/ABI/testing/sysfs-bus-pci

+13 −0
Original line number Diff line number Diff line
@@ -281,3 +281,16 @@ Description: 
		opt-out of driver binding using a driver_override name such as

		"none".  Only a single driver may be specified in the override,

		there is no support for parsing delimiters.



What:		/sys/bus/pci/devices/.../numa_node

Date:		Oct 2014

Contact:	Prarit Bhargava <prarit@redhat.com>

Description:

		This file contains the NUMA node to which the PCI device is

		attached, or -1 if the node is unknown.  The initial value

		comes from an ACPI _PXM method or a similar firmware

		source.  If that is missing or incorrect, this file can be

		written to override the node.  In that case, please report

		a firmware bug to the system vendor.  Writing to this file

		taints the kernel with TAINT_FIRMWARE_WORKAROUND, which

		reduces the supportability of your system.

drivers/pci/pci-sysfs.c

+26 −1
Original line number Diff line number Diff line
@@ -221,12 +221,37 @@ static ssize_t enabled_show(struct device *dev, struct device_attribute *attr, 
static DEVICE_ATTR_RW(enabled);



#ifdef CONFIG_NUMA

static ssize_t numa_node_store(struct device *dev,

			       struct device_attribute *attr, const char *buf,

			       size_t count)

{

	struct pci_dev *pdev = to_pci_dev(dev);

	int node, ret;



	if (!capable(CAP_SYS_ADMIN))

		return -EPERM;



	ret = kstrtoint(buf, 0, &node);

	if (ret)

		return ret;



	if (!node_online(node))

		return -EINVAL;



	add_taint(TAINT_FIRMWARE_WORKAROUND, LOCKDEP_STILL_OK);

	dev_alert(&pdev->dev, FW_BUG "Overriding NUMA node to %d.  Contact your vendor for updates.",

		  node);



	dev->numa_node = node;

	return count;

}



static ssize_t numa_node_show(struct device *dev, struct device_attribute *attr,

			      char *buf)

{

	return sprintf(buf, "%d\n", dev->numa_node);

}

static DEVICE_ATTR_RO(numa_node);

static DEVICE_ATTR_RW(numa_node);

#endif



static ssize_t dma_mask_bits_show(struct device *dev,