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diff --git a/Documentation/edac.txt b/Documentation/edac.txt new file mode 100644 index 0000000..8eda3fb --- /dev/null +++ b/Documentation/edac.txt @@ -0,0 +1,720 @@ + + +EDAC - Error Detection And Correction + +Written by Doug Thompson <dougthompson@xmission.com> +7 Dec 2005 +17 Jul 2007 Updated + + +EDAC is maintained and written by: + + Doug Thompson, Dave Jiang, Dave Peterson et al, + original author: Thayne Harbaugh, + +Contact: + website: bluesmoke.sourceforge.net + mailing list: bluesmoke-devel@lists.sourceforge.net + +"bluesmoke" was the name for this device driver when it was "out-of-tree" +and maintained at sourceforge.net. When it was pushed into 2.6.16 for the +first time, it was renamed to 'EDAC'. + +The bluesmoke project at sourceforge.net is now utilized as a 'staging area' +for EDAC development, before it is sent upstream to kernel.org + +At the bluesmoke/EDAC project site, is a series of quilt patches against +recent kernels, stored in a SVN respository. For easier downloading, there +is also a tarball snapshot available. + +============================================================================ +EDAC PURPOSE + +The 'edac' kernel module goal is to detect and report errors that occur +within the computer system running under linux. + +MEMORY + +In the initial release, memory Correctable Errors (CE) and Uncorrectable +Errors (UE) are the primary errors being harvested. These types of errors +are harvested by the 'edac_mc' class of device. + +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 maintenance and +proactive part replacement of memory DIMMs exhibiting CEs can reduce +the likelihood of the dreaded UE events and system 'panics'. + +NON-MEMORY + +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 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 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. + +In the kernel 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 scannining is skipped for that device. The attribute +is: + + broken_parity_status + +as is located in /sys/devices/pci<XXX>/0000:XX:YY.Z directorys for +PCI devices. + +FUTURE HARDWARE SCANNING + +EDAC will have future error detectors that will be integrated with +EDAC or added to it, 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_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. + + +============================================================================ +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 control and 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 +laid out in a Chip-Select Row (csrowX) and Channel table (chX). There can +be multiple csrows and multiple 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. +Some newer chipsets allow for more than 2 channels, like Fully Buffered DIMMs +(FB-DIMMs). The following example will assume 2 channels: + + + 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 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. +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 similarly 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 '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: + + +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. + + + +Memory Controller name attribute file: + + 'mc_name' + + This attribute file displays the type of memory controller + that is being utilized. + + +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. + +Sdram memory scrubbing rate: + + 'sdram_scrub_rate' + + Read/Write attribute file that controls memory scrubbing. The scrubbing + rate is set by writing a minimum bandwidth in bytes/sec to the attribute + file. The rate will be translated to an internal value that gives at + least the specified rate. + + Reading the file will return the actual scrubbing rate employed. + + If configuration fails or memory scrubbing is not implemented, the value + of the attribute file will be -1. + + + +============================================================================ +'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 contains. + + +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. + Examples: + Registered-DDR + Unbuffered-DDR + + +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 DRAM device is + being utilized on this DIMM. + Examples: + x1 + x2 + x4 + x8 + + +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: + +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: + 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 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: + + +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 + + +Parity Count: + + 'pci_parity_count' + + This attribute file will display the number of parity errors that + have been detected. + + +============================================================================ +MODULE PARAMETERS + +Panic on UE control file: + + 'edac_mc_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: edac_mc_panic_on_ue=[0|1] + + RUN TIME: echo "1" > /sys/module/edac_core/parameters/edac_mc_panic_on_ue + + +Log UE control file: + + 'edac_mc_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: edac_mc_log_ue=[0|1] + + RUN TIME: echo "1" > /sys/module/edac_core/parameters/edac_mc_log_ue + + +Log CE control file: + + 'edac_mc_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: edac_mc_log_ce=[0|1] + + RUN TIME: echo "1" > /sys/module/edac_core/parameters/edac_mc_log_ce + + +Polling period control file: + + 'edac_mc_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 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 Error: + + 'panic_on_pci_parity' + + + This control files 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 of device + +In the header file, edac_core.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 bluesmoke.sourceforget.net website) +installs itself as: + + /sys/devices/systm/edac/test-instance + +in this directory are various controls, a symlink and one or more 'instance' +directorys. + +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 any others to create their own +unique drivers for their hardware systems. + +The 'test_device_edac' sample driver is located at the +bluesmoke.sourceforge.net project site for EDAC. + |
