1 2Configurable sysfs parameters for the x86-64 machine check code. 3 4Machine checks report internal hardware error conditions detected 5by the CPU. Uncorrected errors typically cause a machine check 6(often with panic), corrected ones cause a machine check log entry. 7 8Machine checks are organized in banks (normally associated with 9a hardware subsystem) and subevents in a bank. The exact meaning 10of the banks and subevent is CPU specific. 11 12mcelog knows how to decode them. 13 14When you see the "Machine check errors logged" message in the system 15log then mcelog should run to collect and decode machine check entries 16from /dev/mcelog. Normally mcelog should be run regularly from a cronjob. 17 18Each CPU has a directory in /sys/devices/system/machinecheck/machinecheckN 19(N = CPU number) 20 21The directory contains some configurable entries: 22 23Entries: 24 25bankNctl 26(N bank number) 27 64bit Hex bitmask enabling/disabling specific subevents for bank N 28 When a bit in the bitmask is zero then the respective 29 subevent will not be reported. 30 By default all events are enabled. 31 Note that BIOS maintain another mask to disable specific events 32 per bank. This is not visible here 33 34The following entries appear for each CPU, but they are truly shared 35between all CPUs. 36 37check_interval 38 How often to poll for corrected machine check errors, in seconds 39 (Note output is hexademical). Default 5 minutes. When the poller 40 finds MCEs it triggers an exponential speedup (poll more often) on 41 the polling interval. When the poller stops finding MCEs, it 42 triggers an exponential backoff (poll less often) on the polling 43 interval. The check_interval variable is both the initial and 44 maximum polling interval. 0 means no polling for corrected machine 45 check errors (but some corrected errors might be still reported 46 in other ways) 47 48tolerant 49 Tolerance level. When a machine check exception occurs for a non 50 corrected machine check the kernel can take different actions. 51 Since machine check exceptions can happen any time it is sometimes 52 risky for the kernel to kill a process because it defies 53 normal kernel locking rules. The tolerance level configures 54 how hard the kernel tries to recover even at some risk of 55 deadlock. Higher tolerant values trade potentially better uptime 56 with the risk of a crash or even corruption (for tolerant >= 3). 57 58 0: always panic on uncorrected errors, log corrected errors 59 1: panic or SIGBUS on uncorrected errors, log corrected errors 60 2: SIGBUS or log uncorrected errors, log corrected errors 61 3: never panic or SIGBUS, log all errors (for testing only) 62 63 Default: 1 64 65 Note this only makes a difference if the CPU allows recovery 66 from a machine check exception. Current x86 CPUs generally do not. 67 68trigger 69 Program to run when a machine check event is detected. 70 This is an alternative to running mcelog regularly from cron 71 and allows to detect events faster. 72monarch_timeout 73 How long to wait for the other CPUs to machine check too on a 74 exception. 0 to disable waiting for other CPUs. 75 Unit: us 76 77TBD document entries for AMD threshold interrupt configuration 78 79For more details about the x86 machine check architecture 80see the Intel and AMD architecture manuals from their developer websites. 81 82For more details about the architecture see 83see http://one.firstfloor.org/~andi/mce.pdf 84