Re: [RFC] must fix lists

[Albert Cahalan <albert@users.sf.net>]

On Thu, 2003-10-23 at 19:46, Nick Piggin wrote:
 
> +o alan, Albert Cahalan: 1000 HZ timer increases the need for a stable time
> +  source. Many laptops, SMI can lose ticks. ACPI timers? TSC?

Oh, I have an example for you.

Consider the Intel Plumas chipset. There are
some predictable time windows during which the
RTC will return garbage. The BIOS "fix" leads to
SMI/SMM stuff stealing large chunks of CPU time.
On a logic analyser, somebody at work observed
chunks of time as large as 4 ms. That's 3 to 5
clock ticks. Maybe that isn't worst-case even.

To avoid this disaster, Linux must _never_ touch
the RTC registers. The HPET can be used instead.
The TSC is of course also reliable, but Linux
stops using it as soon as a problem hits!

The ignore-the-TSC code really should be doing
just the opposite. Ticks are likely to be lost.
I've never seen an unstable TSC. :-)

>  o 64-bit dev_t.  Seems almost ready, but it's not really known how much
>    work is still to do.  Patches exist in -mm but with the recent rise of the
>    neo-viro I'm not sure where things are at.

Hey, 32-bit dev_t is in already. That's it. Done.