lkml.org 
[lkml]   [2005]   [Dec]   [26]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH] i386 No Idle HZ aka dynticks 051221
    Hi!

    > I believe the reason why is that the T40 has an extra C state which
    > only shows up if you are running on battery; if you are running on the
    > AC mains, C4 disappears:

    Stupid IBM. I've seen it appearing/disappearing, but did not work out
    when.

    No-C4-on-AC is bad -- if you just disconnect AC and walk away, you are
    running without benefits of C4. Bad. Changing benchmarks depending on
    you booting on AC or battery also look nasty.

    >
    > *C1: type[C1] promotion[C2] demotion[--] latency[001] usage[00000000] time[00000000000000000000]
    > C2: type[C2] promotion[C3] demotion[C1] latency[001] usage[00000000] time[00000000000000000000]
    > C3: type[C3] promotion[C4] demotion[C2] latency[085] usage[00000000] time[00000000000000000000]
    > C4: type[C3] promotion[--] demotion[C3] latency[185] usage[00000000] time[00000000000000000000]
    >
    > With dyntick enabled, the laptop never enters the C4 state, but
    > instead bounces back and forth between C2 and C3 (and I notice that we
    > never enter C1 state, even when the CPU is completely pegged, but
    > that's true with or without dyntick).

    C1 is halt. If your cpu is fully loaded, you don't want to enter any
    sleep state, not even C1.

    > If dyntick is enabled, the laptop enters C4 state, which presumably is
    > a deeper, more power saving state, and it appears power saving effects
    > of dyntick is getting balanced off against the fact that C4 is never
    > getting entered when it is enabled.

    Can you boot on AC power, then go to battery power to verify this theory?

    > Looking at acpi/processor_idle.c, there is all sorts of magic special
    > cases code for the C2 and C3 states (both for promotion/demotion
    > polcies, as well as what to do when idling in those particular
    > states), and which doesn't exist for other states, such as C4.
    > Presumably this explains why we are only never entering C1, and why
    > dyntick enabled C4 never gets reached. What I don't understand is
    > _why_ all of the magic is present for those two states, but not for
    > any of the others.
    >
    > For future work when I have time, is to actually do some performance
    > benchmarks; given that the power consumption doesn't appear to be
    > changed either way with dyntick enabled or disabled, does the time
    > needed to compile a kernel change significantly with or without
    > dyntick?

    It should not change at all. If your cpu is loaded, timers should tick
    as usual, so that you can properly account user/system times of
    processes etc.
    Pavel
    --
    Thanks, Sharp!
    -
    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: 2005-12-26 21:41    [W:2.203 / U:0.148 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site