Reliability, Availability and Serviceability¶

RAS concepts¶

Reliability, Availability and Serviceability (RAS) is a concept used on servers meant to measure their robustness.

Reliability

is the probability that a system will produce correct outputs.

Generally measured as Mean Time Between Failures (MTBF)
Enhanced by features that help to avoid, detect and repair hardware faults

Availability

is the probability that a system is operational at a given time

Generally measured as a percentage of downtime per a period of time
Often uses mechanisms to detect and correct hardware faults in runtime;

Serviceability (or maintainability)

is the simplicity and speed with which a system can be repaired or maintained

Generally measured on Mean Time Between Repair (MTBR)

Improving RAS¶

In order to reduce systems downtime, a system should be capable of detecting hardware errors, and, when possible correcting them in runtime. It should also provide mechanisms to detect hardware degradation, in order to warn the system administrator to take the action of replacing a component before it causes data loss or system downtime.

Among the monitoring measures, the most usual ones include:

CPU – detect errors at instruction execution and at L1/L2/L3 caches;
Memory – add error correction logic (ECC) to detect and correct errors;
I/O – add CRC checksums for transferred data;
Storage – RAID, journal file systems, checksums, Self-Monitoring, Analysis and Reporting Technology (SMART).

By monitoring the number of occurrences of error detections, it is possible to identify if the probability of hardware errors is increasing, and, on such case, do a preventive maintenance to replace a degraded component while those errors are correctable.

Types of errors¶

Most mechanisms used on modern systems use technologies like Hamming Codes that allow error correction when the number of errors on a bit packet is below a threshold. If the number of errors is above, those mechanisms can indicate with a high degree of confidence that an error happened, but they can’t correct.

Also, sometimes an error occur on a component that it is not used. For example, a part of the memory that it is not currently allocated.

That defines some categories of errors:

Correctable Error (CE) - the error detection mechanism detected and corrected the error. Such errors are usually not fatal, although some Kernel mechanisms allow the system administrator to consider them as fatal.
Uncorrected Error (UE) - the amount of errors happened above the error correction threshold, and the system was unable to auto-correct.
Fatal Error - when an UE error happens on a critical component of the system (for example, a piece of the Kernel got corrupted by an UE), the only reliable way to avoid data corruption is to hang or reboot the machine.
Non-fatal Error - when an UE error happens on an unused component, like a CPU in power down state or an unused memory bank, the system may still run, eventually replacing the affected hardware by a hot spare, if available.

Also, when an error happens on a userspace process, it is also possible to kill such process and let userspace restart it.

The mechanism for handling non-fatal errors is usually complex and may require the help of some userspace application, in order to apply the policy desired by the system administrator.

Identifying a bad hardware component¶

Just detecting a hardware flaw is usually not enough, as the system needs to pinpoint to the minimal replaceable unit (MRU) that should be exchanged to make the hardware reliable again.

So, it requires not only error logging facilities, but also mechanisms that will translate the error message to the silkscreen or component label for the MRU.

Typically, it is very complex for memory, as modern CPUs interlace memory from different memory modules, in order to provide a better performance. The DMI BIOS usually have a list of memory module labels, with can be obtained using the dmidecode tool. For example, on a desktop machine, it shows:

Memory Device
        Total Width: 64 bits
        Data Width: 64 bits
        Size: 16384 MB
        Form Factor: SODIMM
        Set: None
        Locator: ChannelA-DIMM0
        Bank Locator: BANK 0
        Type: DDR4
        Type Detail: Synchronous
        Speed: 2133 MHz
        Rank: 2
        Configured Clock Speed: 2133 MHz

On the above example, a DDR4 SO-DIMM memory module is located at the system’s memory labeled as “BANK 0”, as given by the bank locator field. Please notice that, on such system, the total width is equal to the data width. It means that such memory module doesn’t have error detection/correction mechanisms.

Unfortunately, not all systems use the same field to specify the memory bank. On this example, from an older server, dmidecode shows:

Memory Device
        Array Handle: 0x1000
        Error Information Handle: Not Provided
        Total Width: 72 bits
        Data Width: 64 bits
        Size: 8192 MB
        Form Factor: DIMM
        Set: 1
        Locator: DIMM_A1
        Bank Locator: Not Specified
        Type: DDR3
        Type Detail: Synchronous Registered (Buffered)
        Speed: 1600 MHz
        Rank: 2
        Configured Clock Speed: 1600 MHz

There, the DDR3 RDIMM memory module is located at the system’s memory labeled as “DIMM_A1”, as given by the locator field. Please notice that this memory module has 64 bits of data width and 72 bits of total width. So, it has 8 extra bits to be used by error detection and correction mechanisms. Such kind of memory is called Error-correcting code memory (ECC memory).

To make things even worse, it is not uncommon that systems with different labels on their system’s board to use exactly the same BIOS, meaning that the labels provided by the BIOS won’t match the real ones.

ECC memory¶

As mentioned in the previous section, ECC memory has extra bits to be used for error correction. In the above example, a memory module has 64 bits of data width, and 72 bits of total width. The extra 8 bits which are used for the error detection and correction mechanisms are referred to as the syndrome[1][2].

So, when the cpu requests the memory controller to write a word with data width, the memory controller calculates the syndrome in real time, using Hamming code, or some other error correction code, like SECDED+, producing a code with total width size. Such code is then written on the memory modules.

At read, the total width bits code is converted back, using the same ECC code used on write, producing a word with data width and a syndrome. The word with data width is sent to the CPU, even when errors happen.

The memory controller also looks at the syndrome in order to check if there was an error, and if the ECC code was able to fix such error. If the error was corrected, a Corrected Error (CE) happened. If not, an Uncorrected Error (UE) happened.

The information about the CE/UE errors is stored on some special registers at the memory controller and can be accessed by reading such registers, either by BIOS, by some special CPUs or by Linux EDAC driver. On x86 64 bit CPUs, such errors can also be retrieved via the Machine Check Architecture (MCA)[3].

[1]

Please notice that several memory controllers allow operation on a mode called “Lock-Step”, where it groups two memory modules together, doing 128-bit reads/writes. That gives 16 bits for error correction, with significantly improves the error correction mechanism, at the expense that, when an error happens, there’s no way to know what memory module is to blame. So, it has to blame both memory modules.

[2]

Some memory controllers also allow using memory in mirror mode. On such mode, the same data is written to two memory modules. At read, the system checks both memory modules, in order to check if both provide identical data. On such configuration, when an error happens, there’s no way to know what memory module is to blame. So, it has to blame both memory modules (or 4 memory modules, if the system is also on Lock-step mode).

[3]	For more details about the Machine Check Architecture (MCA), please read Configurable sysfs parameters for the x86-64 machine check code at the Kernel tree.

EDAC - Error Detection And Correction¶

Note

“bluesmoke” was the name for this device driver subsystem when it was “out-of-tree” and maintained at http://bluesmoke.sourceforge.net. That site is mostly archaic now and can be used only for historical purposes.

When the subsystem was pushed upstream for the first time, on Kernel 2.6.16, it was renamed to EDAC.

Purpose¶

The edac kernel module’s goal is to detect and report hardware errors that occur within the computer system running under linux.

Memory¶

Memory Correctable Errors (CE) and Uncorrectable Errors (UE) are the primary errors being harvested. These types of errors are harvested by the edac_mc device.

Detecting CE events, then harvesting those events and reporting them, can but must not necessarily be a predictor of future UE events. With CE events only, the system can and will continue to operate as no data has been damaged yet.

However, preventive maintenance and proactive part replacement of memory modules exhibiting CEs can reduce the likelihood of the dreaded UE events and system panics.

Other hardware elements¶

A new feature for EDAC, the edac_device class of device, was added in the 2.6.23 version of the kernel.

This new device type allows for non-memory type of ECC hardware detectors to have their states harvested and presented to userspace via the sysfs interface.

Some architectures have ECC detectors for L1, L2 and L3 caches, along with DMA engines, fabric switches, main data path switches, interconnections, and various other hardware data paths. If the hardware reports it, then a edac_device device probably can be constructed to harvest and present that to userspace.

PCI bus scanning¶

In addition, PCI devices are scanned for PCI Bus Parity and SERR Errors in order to determine if errors are occurring during data transfers.

The presence of PCI Parity errors must be examined with a grain of salt. There are several add-in 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.

There is a PCI device attribute located in sysfs that is checked by the EDAC PCI scanning code. If that attribute is set, PCI parity/error scanning is skipped for that device. The attribute is:

broken_parity_status

and is located in /sys/devices/pci<XXX>/0000:XX:YY.Z directories for PCI devices.

Versioning¶

EDAC is composed of a “core” module (edac_core.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 (or edac_device 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.

Sysfs interface¶

EDAC presents a sysfs interface for control and reporting purposes. It lives in the /sys/devices/system/edac directory.

Within this directory there currently reside 2 components:

mc memory controller(s) system

pci PCI control and status system

Memory Controller (mc) Model¶

Each mc device controls a set of memory modules [4]. These modules are laid out in a Chip-Select Row (csrowX) and Channel table (chX). There can be multiple csrows and multiple channels.

[4]

Nowadays, the term DIMM (Dual In-line Memory Module) is widely used to refer to a memory module, although there are other memory packaging alternatives, like SO-DIMM, SIMM, etc. The UEFI specification (Version 2.7) defines a memory module in the Common Platform Error Record (CPER) section to be an SMBIOS Memory Device (Type 17). Along this document, and inside the EDAC subsystem, the term “dimm” is used for all memory modules, even when they use a different kind of packaging.

Memory controllers allow for several csrows, with 8 csrows being a typical value. Yet, the actual number of csrows depends on the layout of a given motherboard, memory controller and memory module characteristics.

Dual channels allow for dual data length (e. g. 128 bits, on 64 bit systems) data transfers to/from the CPU from/to memory. Some newer chipsets allow for more than 2 channels, like Fully Buffered DIMMs (FB-DIMMs) memory controllers. The following example will assume 2 channels:

CS Rows Channels

ch0 ch1

DIMM_A0 DIMM_B0

csrow0 rank0 rank0

csrow1 rank1 rank1

DIMM_A1 DIMM_B1

csrow2 rank0 rank0

csrow3 rank1 rank1

In the above example, 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 labeled 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. In the example above 2 dual ranked DIMMs are similarly placed. Thus, both csrow0 and csrow1 are populated. On the other hand, when 2 single ranked DIMMs are placed in slots DIMM_A0 and DIMM_B0, then they will have just one csrow (csrow0) and csrow1 will be empty. The pattern repeats itself for csrow2 and csrow3. Also note that some memory controllers don’t have any logic to identify the memory module, see rankX directories below.

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 mcX and csrowX directories are several EDAC control and attribute files.

`mcX` directories¶

In mcX directories are EDAC control and attribute files for this X instance of the memory controllers.

For a description of the sysfs API, please see:

Documentation/ABI/testing/sysfs-devices-edac

`dimmX` or `rankX` directories¶

The recommended way to use the EDAC subsystem is to look at the information provided by the dimmX or rankX directories [5].

A typical EDAC system has the following structure under /sys/devices/system/edac/[6]:

/sys/devices/system/edac/
├── mc
│   ├── mc0
│   │   ├── ce_count
│   │   ├── ce_noinfo_count
│   │   ├── dimm0
│   │   │   ├── dimm_ce_count
│   │   │   ├── dimm_dev_type
│   │   │   ├── dimm_edac_mode
│   │   │   ├── dimm_label
│   │   │   ├── dimm_location
│   │   │   ├── dimm_mem_type
│   │   │   ├── dimm_ue_count
│   │   │   ├── size
│   │   │   └── uevent
│   │   ├── max_location
│   │   ├── mc_name
│   │   ├── reset_counters
│   │   ├── seconds_since_reset
│   │   ├── size_mb
│   │   ├── ue_count
│   │   ├── ue_noinfo_count
│   │   └── uevent
│   ├── mc1
│   │   ├── ce_count
│   │   ├── ce_noinfo_count
│   │   ├── dimm0
│   │   │   ├── dimm_ce_count
│   │   │   ├── dimm_dev_type
│   │   │   ├── dimm_edac_mode
│   │   │   ├── dimm_label
│   │   │   ├── dimm_location
│   │   │   ├── dimm_mem_type
│   │   │   ├── dimm_ue_count
│   │   │   ├── size
│   │   │   └── uevent
│   │   ├── max_location
│   │   ├── mc_name
│   │   ├── reset_counters
│   │   ├── seconds_since_reset
│   │   ├── size_mb
│   │   ├── ue_count
│   │   ├── ue_noinfo_count
│   │   └── uevent
│   └── uevent
└── uevent

In the dimmX directories are EDAC control and attribute files for this X memory module:

size - Total memory managed by this csrow attribute file

This attribute file displays, in count of megabytes, the memory that this csrow contains.
dimm_ue_count - Uncorrectable Errors count attribute file

This attribute file displays the total count of uncorrectable errors that have occurred on this DIMM. If panic_on_ue is set this counter will not have a chance to increment, since EDAC will panic the system.
dimm_ce_count - Correctable Errors count attribute file

This attribute file displays the total count of correctable errors that have occurred on this DIMM. 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.
dimm_dev_type - Device type attribute file
This attribute file will display what type of DRAM device is being utilized on this DIMM. Examples:
x1

x2

x4

x8
dimm_edac_mode - EDAC Mode of operation attribute file

This attribute file will display what type of Error detection and correction is being utilized.
dimm_label - memory module label control file

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.
dimm_location - location of the memory module
The location can have up to 3 levels, and describe how the memory controller identifies the location of a memory module. Depending on the type of memory and memory controller, it can be:
csrow and channel - used when the memory controller doesn’t identify a single DIMM - e. g. in rankX dir;

branch, channel, slot - typically used on FB-DIMM memory controllers;

channel, slot - used on Nehalem and newer Intel drivers.
dimm_mem_type - Memory Type attribute file
This attribute file will display what type of memory is currently on this csrow. Normally, either buffered or unbuffered memory. Examples:
Registered-DDR

Unbuffered-DDR

[5] On some systems, the memory controller doesn’t have any logic to identify the memory module. On such systems, the directory is called rankX and works on a similar way as the csrowX directories. On modern Intel memory controllers, the memory controller identifies the memory modules directly. On such systems, the directory is called dimmX.

[6]	There are also some `power` directories and `subsystem` symlinks inside the sysfs mapping that are automatically created by the sysfs subsystem. Currently, they serve no purpose.

`csrowX` directories¶

When CONFIG_EDAC_LEGACY_SYSFS is enabled, sysfs will contain the csrowX directories. As this API doesn’t work properly for Rambus, FB-DIMMs and modern Intel Memory Controllers, this is being deprecated in favor of dimmX directories.

In the csrowX directories are EDAC control and attribute files for this X instance of csrow:

ue_count - Total Uncorrectable Errors count attribute file

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.
ce_count - Total Correctable Errors count attribute file

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.
size_mb - Total memory managed by this csrow attribute file

This attribute file displays, in count of megabytes, the memory that this csrow contains.
mem_type - Memory Type attribute file
This attribute file will display what type of memory is currently on this csrow. Normally, either buffered or unbuffered memory. Examples:
Registered-DDR

Unbuffered-DDR
edac_mode - EDAC Mode of operation attribute file

This attribute file will display what type of Error detection and correction is being utilized.
dev_type - Device type attribute file
This attribute file will display what type of DRAM device is being utilized on this DIMM. Examples:
x1

x2

x4

x8
ch0_ce_count - Channel 0 CE Count attribute file

This attribute file will display the count of CEs on this DIMM located in channel 0.
ch0_ue_count - Channel 0 UE Count attribute file

This attribute file will display the count of UEs on this DIMM located in channel 0.
ch0_dimm_label - Channel 0 DIMM Label control file

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.
ch1_ce_count - Channel 1 CE Count attribute file

This attribute file will display the count of CEs on this DIMM located in channel 1.
ch1_ue_count - Channel 1 UE Count attribute file

This attribute file will display the count of UEs on this DIMM located in channel 0.
ch1_dimm_label - Channel 1 DIMM Label control file

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 is enabled, then system logs will contain information indicating that errors have been detected:

EDAC MC0: CE page 0x283, offset 0xce0, grain 8, syndrome 0x6ec3, row 0, channel 1 "DIMM_B1": amd76x_edac
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:

Content Example

The memory controller MC0

Error type CE

Memory page 0x283

Offset in the page 0xce0

The byte granularity or resolution of the error grain 8

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 or not. (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 occurred 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:

check_pci_parity - Enable/Disable PCI Parity checking control file
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
pci_parity_count - Parity Count

This attribute file will display the number of parity errors that have been detected.

Module parameters¶

edac_mc_panic_on_ue - Panic on UE control file
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: edac_mc_panic_on_ue=[0|1]
RUN TIME:
echo "1" > /sys/module/edac_core/parameters/edac_mc_panic_on_ue
edac_mc_log_ue - Log UE control file
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: edac_mc_log_ue=[0|1]
RUN TIME:
echo "1" > /sys/module/edac_core/parameters/edac_mc_log_ue
edac_mc_log_ce - Log CE control file
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: edac_mc_log_ce=[0|1]
RUN TIME:
echo "1" > /sys/module/edac_core/parameters/edac_mc_log_ce
edac_mc_poll_msec - Polling period control file
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 the current default. Systems which require all the bandwidth they can get, may increase this.

LOAD TIME:
module/kernel parameter: edac_mc_poll_msec=[0|1]
RUN TIME:
echo "1000" > /sys/module/edac_core/parameters/edac_mc_poll_msec
panic_on_pci_parity - Panic on PCI PARITY Error
This control file enables or disables panicking when a parity error has been detected.

module/kernel parameter:
edac_panic_on_pci_pe=[0|1]
Enable:
echo "1" > /sys/module/edac_core/parameters/edac_panic_on_pci_pe
Disable:
echo "0" > /sys/module/edac_core/parameters/edac_panic_on_pci_pe

EDAC device type¶

In the header file, edac_pci.h, there is a series of edac_device structures and APIs for the EDAC_DEVICE.

User space access to an edac_device is through the sysfs interface.

At the location /sys/devices/system/edac (sysfs) new edac_device devices will appear.

There is a three level tree beneath the above edac directory. For example, the test_device_edac device (found at the http://bluesmoke.sourceforget.net website) installs itself as:

/sys/devices/system/edac/test-instance

in this directory are various controls, a symlink and one or more instance directories.

The standard default controls are:

log_ce boolean to log CE events

log_ue boolean to log UE events

panic_on_ue boolean to panic the system if an UE is encountered (default off, can be set true via startup script)

poll_msec time period between POLL cycles for events

The test_device_edac device adds at least one of its own custom control:

test_bits which in the current test driver does nothing but show how it is installed. A ported driver can add one or more such controls and/or attributes for specific uses. One out-of-tree driver uses controls here to allow for ERROR INJECTION operations to hardware injection registers

The symlink points to the ‘struct dev’ that is registered for this edac_device.

Instances¶

One or more instance directories are present. For the test_device_edac case:

test-instance0

In this directory there are two default counter attributes, which are totals of counter in deeper subdirectories.

ce_count total of CE events of subdirectories

ue_count total of UE events of subdirectories

Blocks¶

At the lowest directory level is the block directory. There can be 0, 1 or more blocks specified in each instance:

test-block0

In this directory the default attributes are:

ce_count which is counter of CE events for this block of hardware being monitored

ue_count which is counter of UE events for this block of hardware being monitored

The test_device_edac device adds 4 attributes and 1 control:

test-block-bits-0 for every POLL cycle this counter is incremented

test-block-bits-1 every 10 cycles, this counter is bumped once, and test-block-bits-0 is set to 0

test-block-bits-2 every 100 cycles, this counter is bumped once, and test-block-bits-1 is set to 0

test-block-bits-3 every 1000 cycles, this counter is bumped once, and test-block-bits-2 is set to 0

reset-counters writing ANY thing to this control will reset all the above counters.

Use of the test_device_edac driver should enable any others to create their own unique drivers for their hardware systems.

The test_device_edac sample driver is located at the http://bluesmoke.sourceforge.net project site for EDAC.

Usage of EDAC APIs on Nehalem and newer Intel CPUs¶

On older Intel architectures, the memory controller was part of the North Bridge chipset. Nehalem, Sandy Bridge, Ivy Bridge, Haswell, Sky Lake and newer Intel architectures integrated an enhanced version of the memory controller (MC) inside the CPUs.

This chapter will cover the differences of the enhanced memory controllers found on newer Intel CPUs, such as i7core_edac, sb_edac and sbx_edac drivers.