Re: TSC instead of ACPI: powerd doesn't work anymore (to be expected?)

From: David O'Brien (obrien_at_freebsd.org)
Date: 10/31/05

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    Date: Sun, 30 Oct 2005 23:58:43 -0800
To: Scott Long <scottl@samsco.org>

    On Sun, Oct 30, 2005 at 07:30:39AM -0700, Scott Long wrote:
    > David O'Brien wrote:
    > >On Sun, Oct 30, 2005 at 02:39:40PM +0800, David Xu wrote:
    > >>David O'Brien wrote:
    > >>>On Fri, Oct 28, 2005 at 03:34:57PM +0200, Alexander Leidinger wrote:
    > >>>
    > >>>>I don't have the message at hand. I just had time to write the mail,
    > >>>>but I
    > >>>>don't have my laptop with me to reproduce the message. But it's easy to
    > >>>>reproduce, just take a PC which is able to make use of powerd and
    > >>>>switch to
    > >>>>using TSC as the timecounter.
    > >>>
    > >>>What is the motivation to use the TSC as a timecounter?
    > >>
    > >>TSC is faster than any others, on many systems, so-called ACPI-fast
    > >>timer is really a slow chip,
    > >
    > >Correct, but why is it felt the latency of the ACPI timer is an issue?
    > >Of course we all want things to as fast as possible, but is that just an
    > >abstract desire, or a real issue was run into?
    >
    > ACPI-fast requires an ioport read which takes about 1us (according to
    > Google). Do that 1000 times a second and you have each CPU spending
    > 1% of its time doing nothing but reading the clock. Yikes.

    But we've lived with using the ACPI timercounter (vs. TSC) for quite a
    while now. Why all of a sudden are the authors of this thread having an
    issue with it now. I know about the recent MySQL thread - but with the
    TSC being untrustable on MP and power managed systems, why is there such
    a desire to use the TSC?
      

    -- 
-- David  (obrien@FreeBSD.org)
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