System time slowdown after upgrading from 2.4 to 2.6

["Ivan Kalatchev" <ivan.kalatchev@esg.ca>]

Hi all,

We have a project that uses PC-104 (ZFx86 100 MHz CPU) Linux box to acquire
some seismological signals. System resides on a M-Systems DiskOnChip 2000.
We have an ISA acquisition card that acquires data into FIFO buffer and
triggers interrupt as soon as 341 points were acquired (then this data is
read out in interrupt handler routine). System worked perfectly well when we
used 2.4.18 kernel. When I printk-ed system time (do_gettimeofday)  in
interrupt routine, at 1kHz sampling frequency interrupts were reported every
341 msec as they should do.
But after I've switched to 2.6 kernel (2.6.7 - preempted, then I tried
2.6.8 - non-preempted) time between successive interrupts at 1kHz became 335
msec, losing 6 msec at each interrupt. What is interesting, when sampling
frequency is 10 kHz, with 2.4.18 kernel interrupts are reported every 34
msec, which is right, but with 2.6 kernels interrupts are coming at 28 msec
interval, again losing same 6 msec!

Any ideas why this might happen?

Please, CC me all answers/comments posted to the list in response to this
posting.
Regards,

Ivan Kalatchev

Senior Software Developer
Engineering Seismology Group Canada Inc.
ISO 9001-2000
1 Hyperion Court, Kingston,
Ontarion, Canada K7K 7G3
phone: (613) 548-8287 ext.247
fax:     (613) 548-8917