Re: [RFC] New Time of day proposal (updated 9/2/04)

From: john stultz (johnstul_at_us.ibm.com)
Date: 09/03/04

  • Next message: Tom Rini: "[PATCH 2.6.9-rc1 3/3] ppc32: Switch arch/ppc/boot to lib/zlib_inflate" 
    To: Dominik Brodowski <linux@dominikbrodowski.de>
Date:	Fri, 03 Sep 2004 12:41:22 -0700

    On Fri, 2004-09-03 at 02:54, Dominik Brodowski wrote:
    > Hi John,
    >
    > Thanks for this exciting code. A few questions:
    >
    > - Where do you intend to put the "delay" code to? Generalize it as well?

    I'm putting that off. Some of the timesources aren't granular enough to
    be used, so I don't see an easy way to cleanly use time source delays
    for some cases and loop delays for others. So I just plan to leave it as
    an arch specific implementation for now.

    > - cpufreq hooks to tsc.c and i386_tsc.c[*] can easily be added. For them to
    > work _better_ than current code: can timeofday_hook() be called (with IRQs
    > disabled) _anywhen_ from kernel context?
    > [*] actually, only one of them needs the notifier, AFAICS...

    Yep, that's on my list. I'm trying to keep to just cleaning up one thing
    at a time, but since I've got to re-work the timer_tsc.c code anyway, I
    figured I'd try to organize all the TSC related functions
    (synchronization, cpufreq, get_cycles(), tsc_delay maybe?) into tsc.c.
    This will simplify things if we ever get around to correctly fixing the
    SMP systems w/ different speed cpus issue.

    > - what about keeping lower-priority timesources still "active" in some sort to
    > a) enable loading _and_ unloading timsources (even modularizing them
    > becoms possible which should make testing easier...),
    > b) call them every couple of seconds to verify the currently used
    > timesource is still sane (and if not, call cpufreq_delayed_get() for
    > example or disable the timesource). This would mean that e.g. pmtmr
    > and pit can be used to "verify" and "backup" tsc, or otherwise...
    > The "clock=tsc" override would only affect the priority of the
    > timesource then, making it so large that no other timesource can
    > "preempt" it, but doesn't avoid making other timesources available
    > for backup and verification purposes.

    That's totally the plan, although I want to put the control into sysfs.
    Load a module, and echo "acpi-pm" or whatever into the sysfs file. I
    just left it out for the first pass so folks would focus on the core
    timeofday and NTP code (I can keep wishing, right? :)

    thanks
    -john

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