Re: Linux 2.2.18: /proc/apm slows system time (was: Linux 2.2.19pre3)

From: Alan Cox (
Date: Sat Dec 30 2000 - 12:01:27 EST

> However, reading from /proc/apm triggers BIOS calls which involve
> certain action, maybe switching to Real Mode and other things, and I
> suspect that either IRQs are still disabled while the BIOS is called or
> the BIOS plays bad games which Linux would have to compensate for. :-/

Looking at the one laptop with this problem I could acquire access to it seems
that the box switches to SMM mode with interrupts disabled for several timer
ticks. During this time the i2c bus is active and it appears to be having a
slow polled conversation with the battery or something attached to the battery
and monitoring it.


        while { true }
                cat /proc/apm

made the box visibly stall and jerk doing X operations

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