In message <[EMAIL PROTECTED]>, Warner Losh writes:
>In message <60866.987710568@critter> Poul-Henning Kamp writes:
>: The BIOS misuse of SMM mode can give you jitter in the 1msec range
>: and there is not much you can do about it. I found out when I
>: clocked a motherboard with a 14.318 derived from a Rb, and timed
>: 1Hz pulses derived from a Cs. Every 400 seconds I ran into the
>: SMM interrupt for about 10 seconds, and all my measurements were
>: late by 800-900 microseconds :-(
>:
>: Intel doesn't care much for precision timing...
>
>Agreed. SMM wasn't turned on on this machine. But there was a disk
>drive that every so often would hammer as a different application
>would core dump. During the core dump, interrupt latency went way up
>for reasons I don't understand. The CPU was a tiny 486 133MHz
>underclocked to 100MHz for cooling.
Then the disk is probably running in PIO mode which thrashes your
interrrupts.
>The pentium systems were much better about this.
Probably because it ran DMA...
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
[EMAIL PROTECTED] | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
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