lkml.org 
[lkml]   [2002]   [Nov]   [9]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    SubjectRe: [PATCH][2.5] notsc option needs some attention/TLC
    Date
    From
    > having this config option ass-backwards is mind-bogglingly confusing,
    > and there seems no real reason for it. John had a plan to just put in
    > CONFIG_X86_PIT instead as the inverse of this, and delete
    > CONFIG_X86_TSC. He seems to have gone off this idea for some reason I
    > can't understand ... I think it solves a lot of these issues ...

    Actually, this is partly my fault. When the subarch code went in, the meaning
    of CONFIG_X86_TSC got altered to mean, 'If not y, don't use tsc at all' (so I
    could disable the TSC entirely for Voyager). Then, when code moved to
    kernel/timers we got some code with the old meaning and some with the new,
    hence the confusion.

    The CONFIG_X86_PIT was something I added to try to clarify. There are three
    cases with this:

    PIT y, TSC n: Never use TSC, always use PIT
    PIT y, TSC y: Try TSC at first, if it doesn't work, fall back to PIT
    PIT n, TSC y: TSC always works, use it without testing.

    Obviously PIT n, TSC n is bogus.

    There are also two distinct usages of TSC:

    1. do_fast_gettimeofday (now in timers) which *requires* the TSCs to be
    synchronised across all CPUs
    2. more accurate udelay (which already has the mechanisms in place to cope
    with TSCs running at different rates).

    1. is usually the reason why numa like machines want to disable the TSC
    entirely.

    Linus isn't very happy with the global TSC disable patch (see
    http://marc.theaimsgroup.com/?t=103652952900006&r=1&w=2). And wants a better
    solution. (Then, of course, there are the additional timer options, like the
    cyclone).

    James





    -
    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to majordomo@vger.kernel.org
    More majordomo info at http://vger.kernel.org/majordomo-info.html
    Please read the FAQ at http://www.tux.org/lkml/

    \
     
     \ /
      Last update: 2005-03-22 13:30    [W:7.377 / U:0.008 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site