arch/x86/include/asm/timer.h:
#define CYC2NS_SCALE_FACTOR 10 /* 2^10, carefully chosen */
static inline unsigned long long __cycles_2_ns(unsigned long long cyc)
{
int cpu = smp_processor_id();
unsigned long long ns = per_cpu(cyc2ns_offset, cpu);
ns += cyc * per_cpu(cyc2ns, cpu) >> CYC2NS_SCALE_FACTOR; // !!!
return ns;
}
Apparently he or she was not very 'careful' to chose CYC2NS_SCALE_FACTOR.
cyc*cyc2ns overflows after (0xffffffffffffffff>>CYC2NS_SCALE_FACTOR)/10^9/60/60/24=208.5 days after
TSC reset. sched_clock should not wrap virtually forever (584years) and many kernel subsystems assume
it; for example the softlockup detector is confused by this;
[18446743993.431771] BUG: soft lockup - CPU#1 stuck for 17163091968s! [???:XXXXX]
Of course the time stamp (18446743993.431771) and 17163091968s (544 years!) are false.
Other problems caused by this overflow include task scheduler unfairness. softlockups ('stuck for 61s!') are
observed in 210~220 days after reboot but I've not yet succeeded to explain the logic.
I believe the problem is not solved in the latest 2.6.32-32.62 kernel packages (from code inspection).
Thanks.
ProblemType: Bug
DistroRelease: Ubuntu 10.04
Package: linux-image-2.6.32-22-server 2.6.32-22.36
Regression: No
Reproducible: Yes
ProcVersionSignature: Ubuntu 2.6.32-22.36-server 2.6.32.11+drm33.2
Uname: Linux 2.6.32-22-server x86_64
AlsaDevices: Error: command ['ls', '-l', '/dev/snd/'] failed with exit code 2: ls: /dev/snd/にアクセスできません: No such file or directory
AplayDevices: Error: [Errno 2] No such file or directory
Architecture: amd64
ArecordDevices: Error: [Errno 2] No such file or directory
Date: Mon Jul 4 15:31:06 2011
InstallationMedia: Ubuntu-Server 10.04.1 LTS "Lucid Lynx" - Release amd64 (20100816.2)
Lsusb:
Bus 002 Device 003: ID 0000:0000
Bus 002 Device 002: ID 8087:0020
Bus 002 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 001 Device 002: ID 8087:0020
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
MachineType: HP ProLiant DL120 G6
PciMultimedia:
ProcCmdLine: BOOT_IMAGE=/boot/vmlinuz-2.6.32-22-server root=UUID=67bbc9ef-18cb-46c3-af61-c6d2e0645c07 ro console=tty console=ttyS0,9600n8 apic=debug crashkernel=384M-2G:64M,2G-:128M quiet
ProcEnviron:
LANG=C
SHELL=/bin/bash
SourcePackage: linux
dmi.bios.date: 09/06/2010
dmi.bios.vendor: HP
dmi.bios.version: O26
dmi.board.name: ProLiant DL120 G6
dmi.board.vendor: Wistron Corporation
dmi.chassis.asset.tag: quest
dmi.chassis.type: 23
dmi.chassis.vendor: HP
dmi.chassis.version: N/A
dmi.modalias: dmi:bvnHP:bvrO26:bd09/06/2010:svnHP:pnProLiantDL120G6:pvr:rvnWistronCorporation:rnProLiantDL120G6:rvr:cvnHP:ct23:cvrN/A:
dmi.product.name: ProLiant DL120 G6
dmi.sys.vendor: HP
> sched_clock should not wrap virtually forever
Actually it is not wrap but jump from 208.5 days to 584 years. cyc2ns_offset is around -100 secs.