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Date: Sat, 5 Sep 1998 08:14:15 -0700 (PDT)
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From: Thomas Dean <tomdean@ix.netcom.com>
To: current@FreeBSD.ORG
Subject: Dmesg Timecounter Varies
Sender: owner-freebsd-current@FreeBSD.ORG
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X-Loop: FreeBSD.ORG

I have noticed that the Timecounter value varies greatly in DMESG.

I am running an SMP kernel.  I extracted the values from
/var/log/messages and passed them thru a stat process:

Timecounter Cost Statistics
Processing /var/log/messages and /var/log/messages.?.gz

  Frequency:     1193182 Hz   - Always this value, unless stated.
  1/freq Time:       838 nsec
  No. Cycles:          3      - floor( mean/(1/freqTime) ).
  Cycle Time:        948 nsec - mean/(no. cycles).
  Overhead:          332 nsec - Total overhead in Timecounter cost.

  Entries:           125      - Number of Timecounter entries in messages.
  Minimum:          2517 nsec
  Maximum:         41603 nsec - Wow! Flyer!
  Mean:             2846 nsec
  Std. Dev.:        3494.46

Notice the maximum flyer.  What causes this variability?

============= dmesg ==================================

FreeBSD 3.0-CURRENT #2: Tue Aug 18 14:05:12 PDT 1998
    root@celebris:/usr/src/sys/compile/CELEBRIS-SMP
Timecounter "i8254"  frequency 1193182 Hz  cost 2540 ns
CPU: Pentium/P54C (586-class CPU)
  Origin = "GenuineIntel"  Id = 0x525  Stepping=5
  Features=0x3bf<FPU,VME,DE,PSE,TSC,MSR,MCE,CX8,APIC>
real memory  = 100663296 (98304K bytes)
avail memory = 95268864 (93036K bytes)
FreeBSD/SMP: Multiprocessor motherboard
 cpu0 (BSP): apic id:  0, version: 0x00030010, at 0xfee00000
 cpu1 (AP):  apic id:  1, version: 0x00030010, at 0xfee00000
 io0 (APIC): apic id:  2, version: 0x000f0011, at 0xfec00000
Probing for devices on PCI bus 0:
chip0:<Intel 82434NX (Neptune)PCI cache memory controller> rev 0x11 on pci0.0.0
ncr0: <ncr 53c810 fast10 scsi> rev 0x02 int a irq 11 on pci0.1.0
...
npx0 on motherboard
npx0: INT 16 interface
Intel Pentium F00F detected, installing workaround
APIC_IO: Testing 8254 interrupt delivery
APIC_IO: routing 8254 via pin 2
changing root device to sd1s1a
SMP: AP CPU #1 Launched!

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