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    SubjectRe: [PATCH 2/3] High-res-timers part 2 (x86 platform code) take 5.1
    On Sun, Oct 13, 2002 at 12:46:31PM +0200, Ingo Adlung wrote:

    > Linus Torvalds wrote:
    > > On Wed, 9 Oct 2002, george anzinger wrote:
    > >
    > >>This patch, in conjunction with the "core" high-res-timers
    > >>patch implements high resolution timers on the i386
    > >>platforms.
    > >
    > >
    > > I really don't get the notion of partial ticks, and quite frankly, this
    > > isn't going into my tree until some major distribution kicks me in the
    > > head and explains to me why the hell we have partial ticks instead of just
    > > making the ticks shorter.

    Not speaking for a major distro, just for me writing HPET (high
    performance event timer ...) support for x86-64 (and it happens to exist
    on ia64 as well, and possibly might be in new Intel P4 chipsets, too).

    It's a very nice piece of hardware that allows very fine granularity
    aperiodic interrupts (in each interrupt you set when the next one will
    happen), without much overhead.

    It'd be a shame to just set this timer to 1kHz periodic just use that as
    a base timer, when you can do much better resolution and latency-wise.
    HPET has a base clock > 10 MHz.

    > > Linus
    >
    > In any kind of virtual environment you would rather prefer a completely
    > tickless system alltogether than increased tick rates. In a S/390
    > virtual machine, running many hundreds of virtual Linux servers the
    > 100Hz timer pops are already considerably painful, and going to a higher
    > tick rate achieving higher timer resolution is completely prohibitive.
    > Similar is true in many embedded systems related to power consumption of
    > high frequency ticks.
    >
    > However, George has shown that introducing the notion of a completely
    > tickless system is expensive on Intel overhead wise, thus partial ticks
    > seem to be a possibility addressing the needs for embedded and virtual
    > environments, getting decent timer resolution as needed.

    When HPET becomes a standard (yes, it's a MS requirement for new PCs),
    it won't be expensive on i386 anymore.

    --
    Vojtech Pavlik
    SuSE Labs
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