cvs commit: src/sys/i386/i386 apic_vector.s local_apic.c mp_machdep.c src/sys/i386/include apicvar.h smp.h src/sys/i386/isa clock.c

[John Baldwin]

On Tuesday 08 February 2005 03:25 pm, John Baldwin wrote:
> jhb         2005-02-08 20:25:07 UTC
>
>   FreeBSD src repository
>
>   Modified files:
>     sys/i386/i386        apic_vector.s local_apic.c mp_machdep.c
>     sys/i386/include     apicvar.h smp.h
>     sys/i386/isa         clock.c
>   Log:
>   Use the local APIC timer to drive the various kernel clocks on SMP
> machines rather than forwarding interrupts from the clock devices around
> using IPIs: - Add an IDT vector that pushes a clock frame and calls
>     lapic_handle_timer().
>   - Add functions to program the local APIC timer including setting the
>     divisor, and setting up the timer to either down a periodic countdown
>     or one-shot countdown.
>   - Add a lapic_setup_clock() function that the BSP calls from
>     cpu_init_clocks() to setup the local APIC timer if it is going to be
>     used.  The setup uses a one-shot countdown to calibrate the timer.  We
>     then program the timer on each CPU to fire at a frequency of hz * 3.
>     stathz is defined as freq / 23 (hz * 3 / 23), and profhz is defined as
>     freq / 2 (hz * 3 / 2).  This gives the clocks relatively prime divisors
>     while keeping a low LCM for the frequency of the clock interrupts.
>     Thanks to Peter Jeremy for suggesting this approach.
>   - Remove the hardclock and statclock forwarding code including the two
>     associated IPIs.  The bitmap IPI handler has now effectively
> degenerated to just IPI_AST.
>   - When the local APIC timer is used we don't turn the RTC on at all, but
>     we still enable interrupts on the ISA timer 0 (i8254) for timecounting
>     purposes.

One caveat at the moment is that if you use ACPI throttle states (not Cx, but 
the hw.acpi.cpu.throttle_* (or whatever it's called now in a post cpufreq 
world) that the timer might operate at a different frequency.  Currently 
there isn't a mechanism for notifying the system when the bus (not CPU clock) 
frequency changes, but once there is this will have to hook into it.

-- 
John Baldwin <jhb at FreeBSD.org>  <><  http://www.FreeBSD.org/~jhb/
"Power Users Use the Power to Serve"  =  http://www.FreeBSD.org