EDAC - Error Detection And Correction
Written by Doug Thompson <norsk5@xmission.com>
7 Dec 2005
EDAC was written by:
Thayne Harbaugh,
modified by Dave Peterson, Doug Thompson, et al,
from the bluesmoke.sourceforge.net project.
============================================================================
EDAC PURPOSE
The 'edac' kernel module goal is to detect and report errors that occur
within the computer system. In the initial release, memory Correctable Errors
(CE) and Uncorrectable Errors (UE) are the primary errors being harvested.
Detecting CE events, then harvesting those events and reporting them,
CAN be a predictor of future UE events. With CE events, the system can
continue to operate, but with less safety. Preventive maintainence and
proactive part replacement of memory DIMMs exhibiting CEs can reduce
the likelihood of the dreaded UE events and system 'panics'.
In addition, PCI Bus Parity and SERR Errors are scanned for on PCI devices
in order to determine if errors are occurring on data transfers.
The presence of PCI Parity errors must be examined with a grain of salt.
There are several addin adapters that do NOT follow the PCI specification
with regards to Parity generation and reporting. The specification says
the vendor should tie the parity status bits to 0 if they do not intend
to generate parity. Some vendors do not do this, and thus the parity bit
can "float" giving false positives.
The PCI Parity EDAC device has the ability to "skip" known flakey
cards during the parity scan. These are set by the parity "blacklist"
interface in the sysfs for PCI Parity. (See the PCI section in the sysfs
section below.) There is also a parity "whitelist" which is used as
an explicit list of devices to scan, while the blacklist is a list
of devices to skip.
EDAC will have future error detectors that will be added or integrated
into EDAC in the following list:
MCE Machine Check Exception
MCA Machine Check Architecture
NMI NMI notification of ECC errors
MSRs Machine Specific Register error cases
and other mechanisms.
These errors are usually bus errors, ECC errors, thermal throttling
and the like.
============================================================================
EDAC VERSIONING
EDAC is composed of a "core" module (edac_mc.ko) and several Memory
Controller (MC) driver modules. On a given system, the CORE
is loaded and one MC driver will be loaded. Both the CORE and
the MC driver have individual versions that reflect current release
level of their respective modules. Thus, to "report" on what version
a system is running, one must report both the CORE's and the
MC driver's versions.
LOADING
If 'edac' was statically linked with the kernel then no loading is
necessary. If 'edac' was built as modules then simply modprobe the
'edac' pieces that you need. You should be able to modprobe
hardware-specific modules and have the dependencies load the necessary core
modules.
Example:
$> modprobe amd76x_edac
loads both the amd76x_edac.ko memory controller module and the edac_mc.ko
core module.
============================================================================
EDAC sysfs INTERFACE
EDAC presents a 'sysfs' interface for control, reporting and attribute
reporting purposes.
EDAC lives in the /sys/devices/system/edac directory. Within this directory
there currently reside 2 'edac' components:
mc memory controller(s) system
pci PCI status system
============================================================================
Memory Controller (mc) Model
First a background on the memory controller's model abstracted in EDAC.
Each mc device controls a set of DIMM memory modules. These modules are
layed out in a Chip-Select Row (csrowX) and Channel table (chX). There can
be multiple csrows and two channels.
Memory controllers allow for several csrows, with 8 csrows being a typical value.
Yet, the actual number of csrows depends on the electrical "loading"
of a given motherboard, memory controller and DIMM characteristics.
Dual channels allows for 128 bit data transfers to the CPU from memory.
Channel 0 Channel 1
===================================
csrow0 | DIMM_A0 | DIMM_B0 |
csrow1 | DIMM_A0 | DIMM_B0 |
===================================
===================================
csrow2 | DIMM_A1 | DIMM_B1 |
csrow3 | DIMM_A1 | DIMM_B1 |
===================================
In the above example table there are 4 physical slots on the motherboard
for memory DIMMs:
DIMM_A0
DIMM_B0
DIMM_A1
DIMM_B1
Labels for these slots are usually silk screened on the motherboard. Slots
labeled 'A' are channel 0 in this example. Slots labled 'B'
are channel 1. Notice that there are two csrows possible on a
physical DIMM. These csrows are allocated their csrow assignment
based on the slot into which the memory DIMM is placed. Thus, when 1 DIMM
is placed in each Channel, the csrows cross both DIMMs.
Memory DIMMs come single or dual "ranked". A rank is a populated csrow.
Thus, 2 single ranked DIMMs, placed in slots DIMM_A0 and DIMM_B0 above
will have 1 csrow, csrow0. csrow1 will be empty. On the other hand,
when 2 dual ranked DIMMs are similiaryly placed, then both csrow0 and
csrow1 will be populated. The pattern repeats itself for csrow2 and
csrow3.
The representation of the above is reflected in the directory tree
in EDAC's sysfs interface. Starting in directory
/sys/devices/system/edac/mc each memory controller will be represented
by its own 'mcX' directory, where 'X" is the index of the MC.
..../edac/mc/
|
|->mc0
|->mc1
|->mc2
....
Under each 'mcX' directory each 'csrowX' is again represented by a
'csrowX', where 'X" is the csrow index:
.../mc/mc0/
|
|->csrow0
|->csrow2
|->csrow3
....
Notice that there is no csrow1, which indicates that csrow0 is
composed of a single ranked DIMMs. This should also apply in both
Channels, in order to have dual-channel mode be operational. Since
both csrow2 and csrow3 are populated, this indicates a dual ranked
set of DIMMs for channels 0 and 1.
Within each of the 'mc','mcX' and 'csrowX' directories are several
EDAC control and attribute files.
============================================================================
DIRECTORY 'mc'
In directory 'mc' are EDAC system overall control and attribute files:
Panic on UE control file:
'panic_on_ue'
An uncorrectable error will cause a machine panic. This is usually
desirable. It is a bad idea to continue when an uncorrectable error
occurs - it is indeterminate what was uncorrected and the operating
system context might be so mangled that continuing will lead to further
corruption. If the kernel has MCE configured, then EDAC will never
notice the UE.
LOAD TIME: module/kernel parameter: panic_on_ue=[0|1]
RUN TIME: echo "1" >/sys/devices/system/edac/mc/panic_on_ue
Log UE control file:
'log_ue'
Generate kernel messages describing uncorrectable errors. These errors
are reported through the system message log system. UE statistics
will be accumulated even when UE logging is disabled.
LOAD TIME: module/kernel parameter: log_ue=[0|1]
RUN TIME: echo "1" >/sys/devices/system/edac/mc/log_ue
Log CE control file:
'log_ce'
Generate kernel messages describing correctable errors. These
errors are reported through the system message log system.
CE statistics will be accumulated even when CE logging is disabled.
LOAD TIME: module/kernel parameter: log_ce=[0|1]
RUN TIME: echo "1" >/sys/devices/system/edac/mc/log_ce
Polling period control file:
'poll_msec'
The time period, in milliseconds, for polling for error information.
Too small a value wastes resources. Too large a value might delay
necessary handling of errors and might loose valuable information for
locating the error. 1000 milliseconds (once each second) is about
right for most uses.
LOAD TIME: module/kernel parameter: poll_msec=[0|1]
RUN TIME: echo "1000" >/sys/devices/system/edac/mc/poll_msec
Module Version read-only attribute file:
'mc_version'
The EDAC CORE modules's version and compile date are shown here to
indicate what EDAC is running.
============================================================================
'mcX' DIRECTORIES
In 'mcX' directories are EDAC control and attribute files for
this 'X" instance of the memory controllers:
Counter reset control file:
'reset_counters'
This write-only control file will zero all the statistical counters
for UE and CE errors. Zeroing the counters will also reset the timer
indicating how long since the last counter zero. This is useful
for computing errors/time. Since the counters are always reset at
driver initialization time, no module/kernel parameter is available.
RUN TIME: echo "anything" >/sys/devices/system/edac/mc/mc0/counter_reset
This resets the counters on memory controller 0
Seconds since last counter reset control file:
'seconds_since_reset'
This attribute file displays how many seconds have elapsed since the
last counter reset. This can be used with the error counters to
measure error rates.
DIMM capability attribute file:
'edac_capability'
The EDAC (Error Detection and Correction) capabilities/modes of
the memory controller hardware.
DIMM Current Capability attribute file:
'edac_current_capability'
The EDAC capabilities available with the hardware
configuration. This may not be the same as "EDAC capability"
if the correct memory is not used. If a memory controller is
capable of EDAC, but DIMMs without check bits are in use, then
Parity, SECDED, S4ECD4ED capabilities will not be available
even though the memory controller might be capable of those
modes with the proper memory loaded.
Memory Type supported on this controller attribute file:
'supported_mem_type'
This attribute file displays the memory type, usually
buffered and unbuffered DIMMs.
Memory Controller name attribute file:
'mc_name'
This attribute file displays the type of memory controller
that is being utilized.
Memory Controller Module name attribute file:
'module_name'
This attribute file displays the memory controller module name,
version and date built. The name of the memory controller
hardware - some drivers work with multiple controllers and
this field shows which hardware is present.
Total memory managed by this memory controller attribute file:
'size_mb'
This attribute file displays, in count of megabytes, of memory
that this instance of memory controller manages.
Total Uncorrectable Errors count attribute file:
'ue_count'
This attribute file displays the total count of uncorrectable
errors that have occurred on this memory controller. If panic_on_ue
is set this counter will not have a chance to increment,
since EDAC will panic the system.
Total UE count that had no information attribute fileY:
'ue_noinfo_count'
This attribute file displays the number of UEs that
have occurred have occurred with no informations as to which DIMM
slot is having errors.
Total Correctable Errors count attribute file:
'ce_count'
This attribute file displays the total count of correctable
errors that have occurred on this memory controller. This
count is very important to examine. CEs provide early
indications that a DIMM is beginning to fail. This count
field should be monitored for non-zero values and report
such information to the system administrator.
Total Correctable Errors count attribute file:
'ce_noinfo_count'
This attribute file displays the number of CEs that
have occurred wherewith no informations as to which DIMM slot
is having errors. Memory is handicapped, but operational,
yet no information is available to indicate which slot
the failing memory is in. This count field should be also
be monitored for non-zero values.
Device Symlink:
'device'
Symlink to the memory controller device
============================================================================
'csrowX' DIRECTORIES
In the 'csrowX' directories are EDAC control and attribute files for
this 'X" instance of csrow:
Total Uncorrectable Errors count attribute file:
'ue_count'
This attribute file displays the total count of uncorrectable
errors that have occurred on this csrow. If panic_on_ue is set
this counter will not have a chance to increment, since EDAC
will panic the system.
Total Correctable Errors count attribute file:
'ce_count'
This attribute file displays the total count of correctable
errors that have occurred on this csrow. This
count is very important to examine. CEs provide early
indications that a DIMM is beginning to fail. This count
field should be monitored for non-zero values and report
such information to the system administrator.
Total memory managed by this csrow attribute file:
'size_mb'
This attribute file displays, in count of megabytes, of memory
that this csrow contatins.
Memory Type attribute file:
'mem_type'
This attribute file will display what type of memory is currently
on this csrow. Normally, either buffered or unbuffered memory.
EDAC Mode of operation attribute file:
'edac_mode'
This attribute file will display what type of Error detection
and correction is being utilized.
Device type attribute file:
'dev_type'
This attribute file will display what type of DIMM device is
being utilized. Example: x4
Channel 0 CE Count attribute file:
'ch0_ce_count'
This attribute file will display the count of CEs on this
DIMM located in channel 0.
Channel 0 UE Count attribute file:
'ch0_ue_count'
This attribute file will display the count of UEs on this
DIMM located in channel 0.
Channel 0 DIMM Label control file:
'ch0_dimm_label'
This control file allows this DIMM to have a label assigned
to it. With this label in the module, when errors occur
the output can provide the DIMM label in the system log.
This becomes vital for panic events to isolate the
cause of the UE event.
DIMM Labels must be assigned after booting, with information
that correctly identifies the physical slot with its
silk screen label. This information is currently very
motherboard specific and determination of this information
must occur in userland at this time.
Channel 1 CE Count attribute file:
'ch1_ce_count'
This attribute file will display the count of CEs on this
DIMM located in channel 1.
Channel 1 UE Count attribute file:
'ch1_ue_count'
This attribute file will display the count of UEs on this
DIMM located in channel 0.
Channel 1 DIMM Label control file:
'ch1_dimm_label'
This control file allows this DIMM to have a label assigned
to it. With this label in the module, when errors occur
the output can provide the DIMM label in the system log.
This becomes vital for panic events to isolate the
cause of the UE event.
DIMM Labels must be assigned after booting, with information
that correctly identifies the physical slot with its
silk screen label. This information is currently very
motherboard specific and determination of this information
must occur in userland at this time.
============================================================================
SYSTEM LOGGING
If logging for UEs and CEs are enabled then system logs will have
error notices indicating errors that have been detected:
MC0: CE page 0x283, offset 0xce0, grain 8, syndrome 0x6ec3, row 0,
channel 1 "DIMM_B1": amd76x_edac
MC0: CE page 0x1e5, offset 0xfb0, grain 8, syndrome 0xb741, row 0,
channel 1 "DIMM_B1": amd76x_edac
The structure of the message is:
the memory controller (MC0)
Error type (CE)
memory page (0x283)
offset in the page (0xce0)
the byte granularity (grain 8)
or resolution of the error
the error syndrome (0xb741)
memory row (row 0)
memory channel (channel 1)
DIMM label, if set prior (DIMM B1
and then an optional, driver-specific message that may
have additional information.
Both UEs and CEs with no info will lack all but memory controller,
error type, a notice of "no info" and then an optional,
driver-specific error message.
============================================================================
PCI Bus Parity Detection
On Header Type 00 devices the primary status is looked at
for any parity error regardless of whether Parity is enabled on the
device. (The spec indicates parity is generated in some cases).
On Header Type 01 bridges, the secondary status register is also
looked at to see if parity ocurred on the bus on the other side of
the bridge.
SYSFS CONFIGURATION
Under /sys/devices/system/edac/pci are control and attribute files as follows:
Enable/Disable PCI Parity checking control file:
'check_pci_parity'
This control file enables or disables the PCI Bus Parity scanning
operation. Writing a 1 to this file enables the scanning. Writing
a 0 to this file disables the scanning.
Enable:
echo "1" >/sys/devices/system/edac/pci/check_pci_parity
Disable:
echo "0" >/sys/devices/system/edac/pci/check_pci_parity
Panic on PCI PARITY Error:
'panic_on_pci_parity'
This control files enables or disables panic'ing when a parity
error has been detected.
module/kernel parameter: panic_on_pci_parity=[0|1]
Enable:
echo "1" >/sys/devices/system/edac/pci/panic_on_pci_parity
Disable:
echo "0" >/sys/devices/system/edac/pci/panic_on_pci_parity
Parity Count:
'pci_parity_count'
This attribute file will display the number of parity errors that
have been detected.
PCI Device Whitelist:
'pci_parity_whitelist'
This control file allows for an explicit list of PCI devices to be
scanned for parity errors. Only devices found on this list will
be examined. The list is a line of hexadecimel VENDOR and DEVICE
ID tuples:
1022:7450,1434:16a6
One or more can be inserted, seperated by a comma.
To write the above list doing the following as one command line:
echo "1022:7450,1434:16a6"
> /sys/devices/system/edac/pci/pci_parity_whitelist
To display what the whitelist is, simply 'cat' the same file.
PCI Device Blacklist:
'pci_parity_blacklist'
This control file allows for a list of PCI devices to be
skipped for scanning.
The list is a line of hexadecimel VENDOR and DEVICE ID tuples:
1022:7450,1434:16a6
One or more can be inserted, seperated by a comma.
To write the above list doing the following as one command line:
echo "1022:7450,1434:16a6"
> /sys/devices/system/edac/pci/pci_parity_blacklist
To display what the whitelist current contatins,
simply 'cat' the same file.
=======================================================================
PCI Vendor and Devices IDs can be obtained with the lspci command. Using
the -n option lspci will display the vendor and device IDs. The system
adminstrator will have to determine which devices should be scanned or
skipped.
The two lists (white and black) are prioritized. blacklist is the lower
priority and will NOT be utilized when a whitelist has been set.
Turn OFF a whitelist by an empty echo command:
echo > /sys/devices/system/edac/pci/pci_parity_whitelist
and any previous blacklist will be utililzed.
