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This is an attempt of providing an interface for memory scrubbing control in EDAC. This patch modifies the EDAC Core to provide the Interface for memory controller modules to implment. The following things are still outstanding: - K8 is the first implemenation, The patch provide a method of configuring the K8 hardware memory scrubber via the 'mcX' sysfs directory. There should be some fallback to a generic scrubber implemented in software if the hardware does not support scrubbing. Or .. the scrubbing sysfs entry should not be visible at all. - Only works with SDRAM, not cache, The K8 can scrub cache and l2cache also - but I think this is not so useful as the cache is busy all the time (one hopes). One would also expect that cache scrubbing requires hardware support. - Error Handling, I would like that errors are returned to the user in "terms of file system". - Presentation, I chose Bandwidth in Bytes/Second as a representation of the scrubbing rate for the following reasons: I like that the sysfs entries are sort-of textual, related to something that makes sense instead of magical values that must be looked up. "My People" wants "% main memory scrubbed per hour" others prefer "% memory bandwidth used" as representation, "bandwith used" makes it easy to calculate both versions in one-liner scripts. If one later wants to scrub cache, the scaling becomes wierd for K8 changing from "blocks of 64 byte memory" to "blocks of 64 cache lines" to "blocks of 64 bit". Using "bandwidth used" makes sense in all three cases, (I.M.O. anyway ;-). - Discovery, There is no way to discover the possible settings and what they do without reading the code and the documentation. *I* do not know how to make that work in a practical way. - Bugs(??), other tools can set invalid values in the memory scrub control register, those will read back as '-1', requiring the user to reset the scrub rate. This is how *I* think it should be. - Afflicting other areas of code, I made changes to edac_mc.c and edac_mc.h which will show up globally - this is not nice, it would be better that the memory scrubbing fuctionality and interface could be entirely contained within the memory controller it applies to. Frithiof Jensen edac_mc.c and its .h file is a CORE helper module for EDAC driver modules. This provides the abstraction for device specific drivers. It is fine to modify this CORE to provide help for new features of the the drivers doug thompson Signed-off-by: Frithiof Jensen <frithiof.jensen@ericson.com> Signed-off-by: doug thompson <norsk5@xmission.com> Acked-by: Alan Cox <alan@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
590 lines
17 KiB
Plaintext
590 lines
17 KiB
Plaintext
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EDAC - Error Detection And Correction
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Written by Doug Thompson <norsk5@xmission.com>
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7 Dec 2005
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EDAC was written by:
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Thayne Harbaugh,
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modified by Dave Peterson, Doug Thompson, et al,
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from the bluesmoke.sourceforge.net project.
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============================================================================
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EDAC PURPOSE
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The 'edac' kernel module goal is to detect and report errors that occur
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within the computer system. In the initial release, memory Correctable Errors
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(CE) and Uncorrectable Errors (UE) are the primary errors being harvested.
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Detecting CE events, then harvesting those events and reporting them,
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CAN be a predictor of future UE events. With CE events, the system can
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continue to operate, but with less safety. Preventive maintenance and
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proactive part replacement of memory DIMMs exhibiting CEs can reduce
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the likelihood of the dreaded UE events and system 'panics'.
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In addition, PCI Bus Parity and SERR Errors are scanned for on PCI devices
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in order to determine if errors are occurring on data transfers.
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The presence of PCI Parity errors must be examined with a grain of salt.
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There are several add-in adapters that do NOT follow the PCI specification
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with regards to Parity generation and reporting. The specification says
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the vendor should tie the parity status bits to 0 if they do not intend
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to generate parity. Some vendors do not do this, and thus the parity bit
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can "float" giving false positives.
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[There are patches in the kernel queue which will allow for storage of
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quirks of PCI devices reporting false parity positives. The 2.6.18
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kernel should have those patches included. When that becomes available,
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then EDAC will be patched to utilize that information to "skip" such
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devices.]
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EDAC will have future error detectors that will be integrated with
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EDAC or added to it, in the following list:
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MCE Machine Check Exception
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MCA Machine Check Architecture
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NMI NMI notification of ECC errors
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MSRs Machine Specific Register error cases
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and other mechanisms.
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These errors are usually bus errors, ECC errors, thermal throttling
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and the like.
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============================================================================
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EDAC VERSIONING
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EDAC is composed of a "core" module (edac_mc.ko) and several Memory
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Controller (MC) driver modules. On a given system, the CORE
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is loaded and one MC driver will be loaded. Both the CORE and
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the MC driver have individual versions that reflect current release
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level of their respective modules. Thus, to "report" on what version
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a system is running, one must report both the CORE's and the
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MC driver's versions.
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LOADING
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If 'edac' was statically linked with the kernel then no loading is
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necessary. If 'edac' was built as modules then simply modprobe the
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'edac' pieces that you need. You should be able to modprobe
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hardware-specific modules and have the dependencies load the necessary core
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modules.
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Example:
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$> modprobe amd76x_edac
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loads both the amd76x_edac.ko memory controller module and the edac_mc.ko
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core module.
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============================================================================
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EDAC sysfs INTERFACE
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EDAC presents a 'sysfs' interface for control, reporting and attribute
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reporting purposes.
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EDAC lives in the /sys/devices/system/edac directory. Within this directory
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there currently reside 2 'edac' components:
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mc memory controller(s) system
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pci PCI control and status system
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============================================================================
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Memory Controller (mc) Model
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First a background on the memory controller's model abstracted in EDAC.
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Each 'mc' device controls a set of DIMM memory modules. These modules are
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laid out in a Chip-Select Row (csrowX) and Channel table (chX). There can
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be multiple csrows and multiple channels.
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Memory controllers allow for several csrows, with 8 csrows being a typical value.
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Yet, the actual number of csrows depends on the electrical "loading"
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of a given motherboard, memory controller and DIMM characteristics.
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Dual channels allows for 128 bit data transfers to the CPU from memory.
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Some newer chipsets allow for more than 2 channels, like Fully Buffered DIMMs
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(FB-DIMMs). The following example will assume 2 channels:
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Channel 0 Channel 1
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===================================
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csrow0 | DIMM_A0 | DIMM_B0 |
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csrow1 | DIMM_A0 | DIMM_B0 |
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===================================
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===================================
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csrow2 | DIMM_A1 | DIMM_B1 |
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csrow3 | DIMM_A1 | DIMM_B1 |
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===================================
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In the above example table there are 4 physical slots on the motherboard
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for memory DIMMs:
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DIMM_A0
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DIMM_B0
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DIMM_A1
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DIMM_B1
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Labels for these slots are usually silk screened on the motherboard. Slots
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labeled 'A' are channel 0 in this example. Slots labeled 'B'
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are channel 1. Notice that there are two csrows possible on a
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physical DIMM. These csrows are allocated their csrow assignment
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based on the slot into which the memory DIMM is placed. Thus, when 1 DIMM
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is placed in each Channel, the csrows cross both DIMMs.
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Memory DIMMs come single or dual "ranked". A rank is a populated csrow.
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Thus, 2 single ranked DIMMs, placed in slots DIMM_A0 and DIMM_B0 above
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will have 1 csrow, csrow0. csrow1 will be empty. On the other hand,
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when 2 dual ranked DIMMs are similarly placed, then both csrow0 and
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csrow1 will be populated. The pattern repeats itself for csrow2 and
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csrow3.
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The representation of the above is reflected in the directory tree
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in EDAC's sysfs interface. Starting in directory
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/sys/devices/system/edac/mc each memory controller will be represented
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by its own 'mcX' directory, where 'X" is the index of the MC.
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..../edac/mc/
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|->mc0
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|->mc1
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|->mc2
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....
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Under each 'mcX' directory each 'csrowX' is again represented by a
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'csrowX', where 'X" is the csrow index:
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.../mc/mc0/
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|->csrow0
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|->csrow2
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|->csrow3
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....
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Notice that there is no csrow1, which indicates that csrow0 is
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composed of a single ranked DIMMs. This should also apply in both
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Channels, in order to have dual-channel mode be operational. Since
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both csrow2 and csrow3 are populated, this indicates a dual ranked
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set of DIMMs for channels 0 and 1.
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Within each of the 'mc','mcX' and 'csrowX' directories are several
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EDAC control and attribute files.
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============================================================================
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DIRECTORY 'mc'
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In directory 'mc' are EDAC system overall control and attribute files:
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Panic on UE control file:
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'panic_on_ue'
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An uncorrectable error will cause a machine panic. This is usually
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desirable. It is a bad idea to continue when an uncorrectable error
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occurs - it is indeterminate what was uncorrected and the operating
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system context might be so mangled that continuing will lead to further
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corruption. If the kernel has MCE configured, then EDAC will never
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notice the UE.
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LOAD TIME: module/kernel parameter: panic_on_ue=[0|1]
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RUN TIME: echo "1" >/sys/devices/system/edac/mc/panic_on_ue
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Log UE control file:
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'log_ue'
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Generate kernel messages describing uncorrectable errors. These errors
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are reported through the system message log system. UE statistics
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will be accumulated even when UE logging is disabled.
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LOAD TIME: module/kernel parameter: log_ue=[0|1]
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RUN TIME: echo "1" >/sys/devices/system/edac/mc/log_ue
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Log CE control file:
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'log_ce'
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Generate kernel messages describing correctable errors. These
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errors are reported through the system message log system.
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CE statistics will be accumulated even when CE logging is disabled.
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LOAD TIME: module/kernel parameter: log_ce=[0|1]
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RUN TIME: echo "1" >/sys/devices/system/edac/mc/log_ce
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Polling period control file:
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'poll_msec'
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The time period, in milliseconds, for polling for error information.
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Too small a value wastes resources. Too large a value might delay
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necessary handling of errors and might loose valuable information for
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locating the error. 1000 milliseconds (once each second) is the current
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default. Systems which require all the bandwidth they can get, may
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increase this.
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LOAD TIME: module/kernel parameter: poll_msec=[0|1]
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RUN TIME: echo "1000" >/sys/devices/system/edac/mc/poll_msec
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============================================================================
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'mcX' DIRECTORIES
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In 'mcX' directories are EDAC control and attribute files for
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this 'X" instance of the memory controllers:
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Counter reset control file:
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'reset_counters'
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This write-only control file will zero all the statistical counters
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for UE and CE errors. Zeroing the counters will also reset the timer
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indicating how long since the last counter zero. This is useful
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for computing errors/time. Since the counters are always reset at
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driver initialization time, no module/kernel parameter is available.
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RUN TIME: echo "anything" >/sys/devices/system/edac/mc/mc0/counter_reset
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This resets the counters on memory controller 0
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Seconds since last counter reset control file:
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'seconds_since_reset'
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This attribute file displays how many seconds have elapsed since the
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last counter reset. This can be used with the error counters to
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measure error rates.
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Memory Controller name attribute file:
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'mc_name'
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This attribute file displays the type of memory controller
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that is being utilized.
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Total memory managed by this memory controller attribute file:
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'size_mb'
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This attribute file displays, in count of megabytes, of memory
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that this instance of memory controller manages.
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Total Uncorrectable Errors count attribute file:
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'ue_count'
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This attribute file displays the total count of uncorrectable
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errors that have occurred on this memory controller. If panic_on_ue
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is set this counter will not have a chance to increment,
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since EDAC will panic the system.
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Total UE count that had no information attribute fileY:
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'ue_noinfo_count'
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This attribute file displays the number of UEs that
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have occurred have occurred with no informations as to which DIMM
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slot is having errors.
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Total Correctable Errors count attribute file:
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'ce_count'
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This attribute file displays the total count of correctable
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errors that have occurred on this memory controller. This
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count is very important to examine. CEs provide early
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indications that a DIMM is beginning to fail. This count
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field should be monitored for non-zero values and report
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such information to the system administrator.
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Total Correctable Errors count attribute file:
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'ce_noinfo_count'
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This attribute file displays the number of CEs that
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have occurred wherewith no informations as to which DIMM slot
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is having errors. Memory is handicapped, but operational,
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yet no information is available to indicate which slot
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the failing memory is in. This count field should be also
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be monitored for non-zero values.
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Device Symlink:
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'device'
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Symlink to the memory controller device.
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Sdram memory scrubbing rate:
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'sdram_scrub_rate'
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Read/Write attribute file that controls memory scrubbing. The scrubbing
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rate is set by writing a minimum bandwith in bytes/sec to the attribute
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file. The rate will be translated to an internal value that gives at
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least the specified rate.
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Reading the file will return the actual scrubbing rate employed.
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If configuration fails or memory scrubbing is not implemented, the value
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of the attribute file will be -1.
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============================================================================
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'csrowX' DIRECTORIES
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In the 'csrowX' directories are EDAC control and attribute files for
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this 'X" instance of csrow:
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Total Uncorrectable Errors count attribute file:
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'ue_count'
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This attribute file displays the total count of uncorrectable
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errors that have occurred on this csrow. If panic_on_ue is set
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this counter will not have a chance to increment, since EDAC
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will panic the system.
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Total Correctable Errors count attribute file:
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'ce_count'
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This attribute file displays the total count of correctable
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errors that have occurred on this csrow. This
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count is very important to examine. CEs provide early
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indications that a DIMM is beginning to fail. This count
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field should be monitored for non-zero values and report
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such information to the system administrator.
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Total memory managed by this csrow attribute file:
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'size_mb'
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This attribute file displays, in count of megabytes, of memory
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that this csrow contains.
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Memory Type attribute file:
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'mem_type'
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This attribute file will display what type of memory is currently
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on this csrow. Normally, either buffered or unbuffered memory.
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Examples:
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Registered-DDR
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Unbuffered-DDR
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EDAC Mode of operation attribute file:
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'edac_mode'
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This attribute file will display what type of Error detection
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and correction is being utilized.
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Device type attribute file:
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'dev_type'
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This attribute file will display what type of DRAM device is
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being utilized on this DIMM.
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Examples:
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x1
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x2
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x4
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x8
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Channel 0 CE Count attribute file:
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'ch0_ce_count'
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This attribute file will display the count of CEs on this
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DIMM located in channel 0.
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Channel 0 UE Count attribute file:
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'ch0_ue_count'
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This attribute file will display the count of UEs on this
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DIMM located in channel 0.
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Channel 0 DIMM Label control file:
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'ch0_dimm_label'
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This control file allows this DIMM to have a label assigned
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to it. With this label in the module, when errors occur
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the output can provide the DIMM label in the system log.
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This becomes vital for panic events to isolate the
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cause of the UE event.
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DIMM Labels must be assigned after booting, with information
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that correctly identifies the physical slot with its
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silk screen label. This information is currently very
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motherboard specific and determination of this information
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must occur in userland at this time.
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Channel 1 CE Count attribute file:
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'ch1_ce_count'
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This attribute file will display the count of CEs on this
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DIMM located in channel 1.
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Channel 1 UE Count attribute file:
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'ch1_ue_count'
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This attribute file will display the count of UEs on this
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DIMM located in channel 0.
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Channel 1 DIMM Label control file:
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'ch1_dimm_label'
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This control file allows this DIMM to have a label assigned
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to it. With this label in the module, when errors occur
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the output can provide the DIMM label in the system log.
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This becomes vital for panic events to isolate the
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cause of the UE event.
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DIMM Labels must be assigned after booting, with information
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that correctly identifies the physical slot with its
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silk screen label. This information is currently very
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motherboard specific and determination of this information
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must occur in userland at this time.
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============================================================================
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SYSTEM LOGGING
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If logging for UEs and CEs are enabled then system logs will have
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error notices indicating errors that have been detected:
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EDAC MC0: CE page 0x283, offset 0xce0, grain 8, syndrome 0x6ec3, row 0,
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channel 1 "DIMM_B1": amd76x_edac
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EDAC MC0: CE page 0x1e5, offset 0xfb0, grain 8, syndrome 0xb741, row 0,
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channel 1 "DIMM_B1": amd76x_edac
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The structure of the message is:
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the memory controller (MC0)
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Error type (CE)
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memory page (0x283)
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offset in the page (0xce0)
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the byte granularity (grain 8)
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or resolution of the error
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the error syndrome (0xb741)
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memory row (row 0)
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memory channel (channel 1)
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DIMM label, if set prior (DIMM B1
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and then an optional, driver-specific message that may
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have additional information.
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Both UEs and CEs with no info will lack all but memory controller,
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error type, a notice of "no info" and then an optional,
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driver-specific error message.
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============================================================================
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PCI Bus Parity Detection
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On Header Type 00 devices the primary status is looked at
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for any parity error regardless of whether Parity is enabled on the
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device. (The spec indicates parity is generated in some cases).
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On Header Type 01 bridges, the secondary status register is also
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looked at to see if parity occurred on the bus on the other side of
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the bridge.
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SYSFS CONFIGURATION
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Under /sys/devices/system/edac/pci are control and attribute files as follows:
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Enable/Disable PCI Parity checking control file:
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'check_pci_parity'
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This control file enables or disables the PCI Bus Parity scanning
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operation. Writing a 1 to this file enables the scanning. Writing
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a 0 to this file disables the scanning.
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Enable:
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echo "1" >/sys/devices/system/edac/pci/check_pci_parity
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Disable:
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echo "0" >/sys/devices/system/edac/pci/check_pci_parity
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Panic on PCI PARITY Error:
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'panic_on_pci_parity'
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This control files enables or disables panicking when a parity
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error has been detected.
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module/kernel parameter: panic_on_pci_parity=[0|1]
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Enable:
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echo "1" >/sys/devices/system/edac/pci/panic_on_pci_parity
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Disable:
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echo "0" >/sys/devices/system/edac/pci/panic_on_pci_parity
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Parity Count:
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'pci_parity_count'
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This attribute file will display the number of parity errors that
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have been detected.
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=======================================================================
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