Time jumping on both 4.x and 5.x ...

Marc G. Fournier scrappy at hub.org
Fri Nov 28 20:39:10 PST 2003

On Fri, 28 Nov 2003, Kris Kennaway wrote:

> On Fri, Nov 28, 2003 at 09:32:30PM -0400, Marc G. Fournier wrote:
> >
> > In trying to isolate an issue where the PostgreSQL 'explain analyze' is
> > showing "odd results" (namely, negative time estimates on queries), Tom
> > Lane wrote a quick C program to test gettimeofday() (program attached) ...
> > the results on a 4.9-PRERELEASE kernel of Sep 20 14:16:48 ADT 2003 shows:
> >
> > neptune# time ./timetest
> > out of order tv_sec: 1070068479 99040, prev 1070069174 725235
> > out of order tv_usec: 1070068479 99040, prev 1070069174 725235
> > out of order tv_sec: 1070069175 19687, prev 1070068479 99040
> > out of order tv_usec: 1070069175 19687, prev 1070068479 99040
> > out of order tv_sec: 1070068499 99377, prev 1070069194 625573
> > out of order tv_usec: 1070068499 99377, prev 1070069194 625573
> > out of order tv_sec: 1070069194 808542, prev 1070068499 99377
> > ^C1.171u 23.461s 0:24.68 99.7%  5+169k 1+0io 0pf+0w
> >
> > One person on the list has tried the same script on a 5.2 kernel, and
> > reports seeing similar results, but after a longer period of time (~30min)
> > ...
> What hardware, kernel configuration, etc?  Do you have a misconfigured
> ntpd/timed that is manually flapping the time around?

Hardware for the above is a Dual-Xeon, 4Gig of RAM, and about 421
processes running on it currently ... kernel config is at the bottom, but
I don't think there is anything 'abnormal' about it ... and note that I've
had others be able to reproduce the problem on both 4.x and 5.x systems

as to ntpd/timed ... don't run either ... run ntpdate twice a day (11:59
and 23:59), but that is it as far as playing with the clock is concerned

Marc G. Fournier           Hub.Org Networking Services (http://www.hub.org)
Email: scrappy at hub.org           Yahoo!: yscrappy              ICQ: 7615664

machine         i386
cpu             I686_CPU
ident           kernel
maxusers        0

makeoptions     DEBUG=-g                #Build kernel with gdb(1) debug symbols

options         NMBCLUSTERS=16384

options         VM_KMEM_SIZE="(400*1024*1024)"
options         VM_KMEM_SIZE_MAX="(400*1024*1024)"

options         NULLFS                  #NULL filesystem
options         UNION                   #Union filesystem
options         NFS                     #Network File System
options         COMPAT_LINUX

options         INET                    #InterNETworking
options         FFS                     #Berkeley Fast Filesystem
options         FFS_ROOT                #FFS usable as root device [keep this!]
options         SOFTUPDATES             #Enable FFS soft updates support
options         UFS_DIRHASH             #Improve performance on big directories
options         PROCFS                  #Process filesystem
options         COMPAT_43               #Compatible with BSD 4.3 [KEEP THIS!]
options         SCSI_DELAY=15000        #Delay (in ms) before probing SCSI
options         KTRACE                  #ktrace(1) support

options         SYSVSHM
options         SHMMAXPGS=199608
options         SHMMAX=(SHMMAXPGS*PAGE_SIZE+1)

options         SYSVSEM
options         SEMMNI=4096
options         SEMMNS=8192

options         SYSVMSG                 #SYSV-style message queues

options         P1003_1B                #Posix P1003_1B real-time extensions
options         ICMP_BANDLIM            #Rate limit bad replies
options         KBD_INSTALL_CDEV        # install a CDEV entry in /dev

options         SMP                     # Symmetric MultiProcessor Kernel
options         APIC_IO                 # Symmetric (APIC) I/O

device          isa
device          pci

device          ahd             # AHA39320/29320 and onboard AIC79xx devices

options         AHD_REG_PRETTY_PRINT    # Print register bitfields in debug
                                        # output.  Adds ~215k to driver.

device          scbus           # SCSI bus (required)
device          da              # Direct Access (disks)
device          pass            # Passthrough device (direct SCSI access)
device          ses

device          atkbdc0 at isa? port IO_KBD
device          atkbd0  at atkbdc? irq 1 flags 0x1
device          psm0    at atkbdc? irq 12

device          vga0    at isa?

pseudo-device   splash

device          sc0     at isa? flags 0x100

device          npx0    at nexus? port IO_NPX irq 13

device          em              # Intel PRO/1000 adapter Gigabit Ethernet Card (

pseudo-device   loop            # Network loopback
pseudo-device   ether           # Ethernet support
pseudo-device   pty     256     # Pseudo-ttys (telnet etc)

pseudo-device   bpf             #Berkeley packet filter

options         DDB
options         DDB_UNATTENDED
options         INCLUDE_CONFIG_FILE     # Include this file in kernel

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