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

From: Scott Long (scottl_at_samsco.org)
Date: 10/30/05

  • Next message: Poul-Henning Kamp: "Re: TSC instead of ACPI: powerd doesn't work anymore (to be expected?)" 
    Date: Sun, 30 Oct 2005 07:03:57 -0700
To: David Xu <davidxu@freebsd.org>

    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, at least far slower than reading from RAM,
    > manufactories
    > just lie on this.
    >
    > Regards,
    > David Xu
    >

    Kind of. The TSC is internal to the CPU and can be read without any
    memory accesses or synchronization. The ACPI-faster counter needs to
    be read with an ioport instruction, which is exceedingly slow on
    modern hardware. ACPI-safe needs _three_ ioport reads.

    Scott
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