Date: Tue, 8 Feb 2005 17:52:35 -0500 From: John Baldwin <jhb@FreeBSD.org> To: "M. Warner Losh" <imp@bsdimp.com> Cc: cvs-all@FreeBSD.org Subject: Re: 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 Message-ID: <200502081752.35022.jhb@FreeBSD.org> In-Reply-To: <20050208.140749.52472160.imp@bsdimp.com> References: <200502082025.j18KP72E069507@repoman.freebsd.org> <200502081550.55445.jhb@FreeBSD.org> <20050208.140749.52472160.imp@bsdimp.com>
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On Tuesday 08 February 2005 04:07 pm, M. Warner Losh wrote:
> In message: <200502081550.55445.jhb@FreeBSD.org>
>
> John Baldwin <jhb@FreeBSD.org> writes:
> : 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.
>
> Relying on a frequency that can change will lead to really bad time
> keeping, even if there were a notification mechanism. TSC should be
> the only one that's impacted by changes to the clock speed. All the
> other time keeping mechanisms are independent of CPU clock speed.
Note that this is not for {bin,micro,nano}{up,}time(), but to drive
{hard,soft,stat}clock(). There is a difference between the two things.
Specifically, this is not a timecounter device.
--
John Baldwin <jhb@FreeBSD.org> <>< http://www.FreeBSD.org/~jhb/
"Power Users Use the Power to Serve" = http://www.FreeBSD.org
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