path: root/Documentation/ABI
diff options
authorPrarit Bhargava <prarit@redhat.com>2014-10-23 14:22:12 -0400
committerBjorn Helgaas <bhelgaas@google.com>2014-11-06 15:10:06 -0700
commit63692df103e9c76b26c382ce8079283b7df9a99a (patch)
tree677204f229cd7ad3dcf072d8d7eb44ce01018e9e /Documentation/ABI
parentf114040e3ea6e07372334ade75d1ee0775c355e1 (diff)
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: Prarit Bhargava <prarit@redhat.com> Signed-off-by: Bjorn 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>
Diffstat (limited to 'Documentation/ABI')
1 files changed, 13 insertions, 0 deletions
diff --git a/Documentation/ABI/testing/sysfs-bus-pci b/Documentation/ABI/testing/sysfs-bus-pci
index ee6c04036492..b3bc50f650ee 100644
--- a/Documentation/ABI/testing/sysfs-bus-pci
+++ b/Documentation/ABI/testing/sysfs-bus-pci
@@ -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>
+ 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.

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