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

From: Peter Jeremy (PeterJeremy_at_optushome.com.au)
Date: 10/31/05

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    Date: Tue, 1 Nov 2005 05:00:37 +1100
To: Poul-Henning Kamp <phk@phk.freebsd.dk>

    On Mon, 2005-Oct-31 11:26:38 +0100, Poul-Henning Kamp wrote:
    >In message <4365EF7B.1020706@freebsd.org>, David Xu writes:
    >>We can introduce
    >>hrtime_t clock_gethrtime(clockid_t clock) to get hi-resolution time
    >>as the one seen in RTLinux, or gethrtime() as seen in Solaris (Daniel
    >>Eischen said?)
    ...
    >The open group specifically allow clock_gettime() to implement
    >more timescales, so what did those fools go and invent even more
    >library functions for ?

    gethrtime() dates back to SunOS 4.x and (AFAIK) predates TOG's work.
    ISTR it's not really a syscall but just reads the HR clock out of
    the magic page with the timer.

    I'd also support a move to make gettimeofday() a cheaper syscall
    that counts in 1/hz and require the use of clock_gettime() for
    accurate timestamps.

    This still leaves the issue of the scheduler - do we need an accurate
    (and expensive) record of how long a particular process executes? We
    can probably make the timestamps slightly cheaper to obtain since we
    only need to keep track of a time difference on a single CPU - there's
    no need for inter-CPU synchronisation (because a thread can't migrate
    from from CPU to CPU without the scheduler knowing). It probably
    doesn't even matter if the time intervals provided to the scheduler
    are inaccurate by a few percent or differ slightly between CPUs. 

    -- 
Peter Jeremy
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