Re: [RFC][PATCH] new timeofday i386 hooks (v.A0)

George Anzinger
2004-09-03T01:52:00Z

john stultz wrote:
> All,
> This patch implements the minimal i386 architecture hooks to enable the
> new time of day subsystem code. It applies on top of my
> linux-2.6.9-rc1_timeofday-core_A0 patch and with this patch applied, you
> can test the new time of day subsystem on i386. Basically it adds the
> call to timeofday_interrupt_hook() and cuts alot of code out of the
> build. The only new code is the sync_persistant_clock() function which
> is mostly ripped out of do_timer_interrupt(). Pretty un-interesting.
>
> I look forward to your comments and feedback.
>
> thanks
> -john
>
> linux-2.6.9-rc1_timeofday-i386_A0.patch
> =======================================
> diff -Nru a/arch/i386/Kconfig b/arch/i386/Kconfig
> --- a/arch/i386/Kconfig 2004-09-02 13:29:59 -07:00
> +++ b/arch/i386/Kconfig 2004-09-02 13:29:59 -07:00
> @@ -14,6 +14,10 @@
> 486, 586, Pentiums, and various instruction-set-compatible chips by
> AMD, Cyrix, and others.
>
> +config NEWTOD
> + bool
> + default y
> +
> config MMU
> bool
> default y
> diff -Nru a/arch/i386/kernel/time.c b/arch/i386/kernel/time.c
> --- a/arch/i386/kernel/time.c 2004-09-02 13:29:59 -07:00
> +++ b/arch/i386/kernel/time.c 2004-09-02 13:29:59 -07:00
> @@ -67,6 +67,8 @@
>
> #include "io_ports.h"
>
> +#include <linux/timeofday.h>
> +
> extern spinlock_t i8259A_lock;
> int pit_latch_buggy; /* extern */
>
> @@ -87,6 +89,7 @@
>
> struct timer_opts *cur_timer = &timer_none;
>
> +#ifndef CONFIG_NEWTOD
> /*
> * This version of gettimeofday has microsecond resolution
> * and better than microsecond precision on fast x86 machines with TSC.
> @@ -169,6 +172,7 @@
> }
>
> EXPORT_SYMBOL(do_settimeofday);
> +#endif
>
> static int set_rtc_mmss(unsigned long nowtime)
> {
> @@ -194,12 +198,39 @@
> * Note: This function is required to return accurate
> * time even in the absence of multiple timer ticks.
> */
> +#ifndef CONFIG_NEWTOD
> unsigned long long monotonic_clock(void)
> {
> return cur_timer->monotonic_clock();
> }
> EXPORT_SYMBOL(monotonic_clock);
> +#endif
>
> +void sync_persistant_clock(struct timespec ts)
> +{
> + /*
> + * If we have an externally synchronized Linux clock, then update
> + * CMOS clock accordingly every ~11 minutes. Set_rtc_mmss() has to be
> + * called as close as possible to 500 ms before the new second starts.
> + */
> + if (ts.tv_sec > last_rtc_update + 660 &&
> + (ts.tv_nsec / 1000)
> + >= USEC_AFTER - ((unsigned) TICK_SIZE) / 2 &&
> + (ts.tv_nsec / 1000)
> + <= USEC_BEFORE + ((unsigned) TICK_SIZE) / 2) {
> + /* horrible...FIXME */
> + if (efi_enabled) {
> + if (efi_set_rtc_mmss(ts.tv_sec) == 0)
> + last_rtc_update = ts.tv_sec;
> + else
> + last_rtc_update = ts.tv_sec - 600;
> + } else if (set_rtc_mmss(ts.tv_sec) == 0)
> + last_rtc_update = ts.tv_sec;
> + else
> + last_rtc_update = ts.tv_sec - 600; /* do it again in 60 s */
> + }
> +
I have wondered, and continue to do so, why this is not a timer driven function.
It just seems silly to check this every interrupt when we have low overhead
timers for just this sort of thing.

I wonder about the load calc in the same way...

Now, the question is how do you hook up the timer list. We MUST be able to
start a timer that will run for several min to hours and have it expire such
that the wall time difference is "really" close to what was requested. This
requires some "lock up" between the wall clock and the timer subsystem.

What are your thoughts here?

George

--
George Anzinger george@mvista.com
High-res-timers: http://sourceforge.net/projects/high-res-timers/
Preemption patch: http://www.kernel.org/pub/linux/kernel/people/rml