Re: clocksource change of behavior in 2.6.22 compared to 2.6.20 causes massive system clock slowdown

[Tilman Schmidt <tilman@imap.cc>]

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John,

I see the same change in behaviour on my newish Pentium D 940.
Here's what I posted this Monday to the "clocksource tsc unstable"
thread, mistakenly thinking it belonged there:

<quote>
Now that you mention it - I am seeing something similar with
kernel 2.6.22 on an Intel Pentium D 940 dual core processor
(arbitrary selection of dmesg lines that appeared relevant):

<5>[    0.000000] Linux version 2.6.22-testing (ts@xenon) (gcc version 4.1.2 20061115 (prerelease) (SUSE Linux)) #1 SMP PREEMPT Mon Jul 9 10:57:22 CEST 2007
<6>[   56.367608] hpet0: at MMIO 0xfed00000, IRQs 2, 8, 0
<6>[   56.367867] hpet0: 3 64-bit timers, 14318180 Hz
<4>[   56.428897] Calibrating delay using timer specific routine.. 6399.40 BogoMIPS (lpj=3199704)
<4>[   56.438058] CPU0: Intel(R) Pentium(R) D CPU 3.20GHz stepping 04
<4>[   56.509321] CPU1: Intel(R) Pentium(R) D CPU 3.20GHz stepping 04
<6>[   56.510299] Total of 2 processors activated (12793.06 BogoMIPS).
<4>[   56.510527] ENABLING IO-APIC IRQs
<6>[   56.510792] ..TIMER: vector=0x31 apic1=0 pin1=2 apic2=-1 pin2=-1
<6>[   56.622869] checking TSC synchronization [CPU#0 -> CPU#1]:
<4>[   56.642971] Measured 16 cycles TSC warp between CPUs, turning off TSC clock.
<4>[    0.152000] Marking TSC unstable due to: check_tsc_sync_source failed.
<6>[    0.153000] Brought up 2 CPUs
<4>[    0.241000] migration_cost=2000

2.6.22-rc6-mm1 has it too, though without the backward jump in
printk timestamps:

<5>[    0.000000] Linux version 2.6.22-rc6-mm1-testing (ts@xenon) (gcc version 4.1.2 20061115 (prerelease) (SUSE Linux)) #10 SMP PREEMPT Thu Jul 5 23:41:32 CEST
2007
<6>[    0.160000] Total of 2 processors activated (12791.39 BogoMIPS).
<4>[    0.160000] ENABLING IO-APIC IRQs
<6>[    0.161000] ..TIMER: vector=0x31 apic1=0 pin1=2 apic2=-1 pin2=-1
<6>[    0.171000] checking TSC synchronization [CPU#0 -> CPU#1]:
<4>[    0.171005] Measured 96 cycles TSC warp between CPUs, turning off TSC clock.
<4>[    0.171005] Marking TSC unstable due to: check_tsc_sync_source failed.
<6>[    0.172000] Brought up 2 CPUs

2.6.21.6 is fine here, though:

<5>[    0.000000] Linux version 2.6.21.6-noinitrd (ts@xenon) (gcc version 4.1.2 20061115 (prerelease) (SUSE Linux)) #1 SMP PREEMPT Sat Jul 7 16:40:13 CEST 2007
<6>[   59.776179] Total of 2 processors activated (12794.21 BogoMIPS).
<4>[   59.776403] ENABLING IO-APIC IRQs
<6>[   59.776657] ..TIMER: vector=0x31 apic1=0 pin1=2 apic2=-1 pin2=-1
<6>[   59.923347] checking TSC synchronization [CPU#0 -> CPU#1]: passed.
<6>[   59.943479] Brought up 2 CPUs
<4>[   60.198497] migration_cost=496
<6>[   60.303586] Time: tsc clocksource has been installed.
<6>[   60.303678] Switched to high resolution mode on CPU 0
<6>[   60.303974] Switched to high resolution mode on CPU 1

HTH
</quote>

Please let me know if you need the full dmesgs, or anything else.

Thanks
T.

-- 
Tilman Schmidt                    E-Mail: tilman@imap.cc
Bonn, Germany
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