Re: [RFC] must fix lists

From: Albert Cahalan (albert_at_users.sf.net)
Date: 10/24/03

  • Next message: Ernie Petrides: "Re: posix capabilities inheritance" 
    To: Nick Piggin <piggin@cyberone.com.au>
Date:	23 Oct 2003 21:06:57 -0400

    On Thu, 2003-10-23 at 19:46, Nick Piggin wrote:
     
    > +o alan, Albert Cahalan: 1000 HZ timer increases the need for a stable time
    > + source. Many laptops, SMI can lose ticks. ACPI timers? TSC?

    Oh, I have an example for you.

    Consider the Intel Plumas chipset. There are
    some predictable time windows during which the
    RTC will return garbage. The BIOS "fix" leads to
    SMI/SMM stuff stealing large chunks of CPU time.
    On a logic analyser, somebody at work observed
    chunks of time as large as 4 ms. That's 3 to 5
    clock ticks. Maybe that isn't worst-case even.

    To avoid this disaster, Linux must _never_ touch
    the RTC registers. The HPET can be used instead.
    The TSC is of course also reliable, but Linux
    stops using it as soon as a problem hits!

    The ignore-the-TSC code really should be doing
    just the opposite. Ticks are likely to be lost.
    I've never seen an unstable TSC. :-)

    > o 64-bit dev_t. Seems almost ready, but it's not really known how much
    > work is still to do. Patches exist in -mm but with the recent rise of the
    > neo-viro I'm not sure where things are at.

    Hey, 32-bit dev_t is in already. That's it. Done.

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  • Next message: Ernie Petrides: "Re: posix capabilities inheritance"

    Relevant Pages

    • Re: summary (Re: [patch] prefer TSC over PM Timer)
      ... We should prefer the TSC here ... ticks allows for time inconsistencies. ... inaccuracies and possible inconsistencies. ... send the line "unsubscribe linux-kernel" in ...
      (Linux-Kernel)
    • Re: Losing too many ticks! .... on a VIA epia board
      ... > Losing some ticks... ... > Incorrect TSC synchronization on an SMP system. ... > Falling back to a sane timesource now. ...
      (Linux-Kernel)
    • Re: summary (Re: [patch] prefer TSC over PM Timer)
      ... >>short term between tick interpolation and also to detect and correct for PIT ... We should prefer the TSC here ... > ticks allows for time inconsistencies. ...
      (Linux-Kernel)
    • Re: TSC cannot be used as a time source?
      ... > Incorrect TSC synchronization on an SMP system. ... >I installed the server I used the same timesource I use on other ... Time keeping in Linux is done by an interrupt which occurs regularly ... of the counter at each of the interrupts. ...
      (Fedora)
    • RE: [patch] prefer TSC over PM Timer
      ... and my measurements show it in the same performance ballpark as TSC. ... wouldn't local apic timer be a lot better for NUMA too? ... send the line "unsubscribe linux-kernel" in ...
      (Linux-Kernel)