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    Subject2.6.21-rc5-mm3 - cpuidle, acpi, and C-states
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    On Fri, 30 Mar 2007 01:05:59 PDT, Andrew Morton said:
    > ftp://ftp.kernel.org/pub/linux/kernel/people/akpm/patches/2.6/2.6.21-rc5/2.6.21-rc5-mm3/

    Somebody is confused (possibly me). Running an x86_64 kernel, and I have:

    % cat /proc/acpi/processor/CPU0/power
    active state: C0
    max_cstate: C8
    bus master activity: 00000000
    maximum allowed latency: 2000 usec
    states:
    C1: type[C1] promotion[--] demotion[--] latency[001] usage[00000003] duration[00000000000000000000]
    C2: type[C2] promotion[--] demotion[--] latency[001] usage[00166266] duration[00000000000000000000]
    C3: type[C3] promotion[--] demotion[--] latency[057] usage[02045938] duration[00000000000000000000]

    Wow. Lots of zeros in that last column..

    The 'duration' is output by this code in drivers/acpi/processor_idle.c that
    thinks the value is an 'unsigned long long':

    seq_printf(seq, "latency[%03d] usage[%08d] duration[%020llu]\n",
    pr->power.states[i].latency,
    pr->power.states[i].usage,
    (unsigned long long)pr->power.states[i].time);

    However, over in /sys, we have non-zero values for the usage/time:

    % cat /sys/devices/system/cpu/cpu0/cpuidle/state?/time
    0
    110861364
    -2091818383

    That's because in drivers/cpuidle/sysfs.c, we have this code that thinks
    a %d is suitable to output that number:

    #define define_show_state_function(_name) static ssize_t show_state_##_name(struct cpuidle_state *state, char *buf) { \
    return sprintf(buf, "%d\n", state->_name);\
    }
    ...
    define_one_state_ro(time, show_state_time);

    But the negative number for state2/time indicates that *this* isn't right either....
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