Re: ACPI PM-Timer [Was: Re: [RFC][PATCH] must fix lists]

[john stultz <johnstul@us.ibm.com>]

On Mon, 2003-10-27 at 10:24, Dominik Brodowski wrote:
> On Mon, Oct 27, 2003 at 11:53:43PM +1100, 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?
> 
> A few months ago, I proposed to make the ACPI "Powermanagement" timer, a 
> reliable timing source with  ~3.6MHz resolution, available as a timer_opts
> for arch/i386/kernel/timers/timer.c. [1]
> 
> The major difficulty with this ACPI PM-Timer is that the I/O-port it is
> located at is unknown during time_init.[2] So, it becomes necessary to use a
> different timing source in the beginning, and switch to the ACPI PM-Timer
> later.
> 
> Here are two different methods to replace one timing source with another.
> First, the simple (and buggy) one -- the timing is broken until the next
> timer "tick" == the next call to mark_offset().

Thanks for working on this, Dominik!  

My only comment is that rather then replacing the time source midstream,
could we not do as the HPET time source does and use the late_time_init
callback? That avoids the nasty time source switching code. 

thanks
-john