lkml.org 
[lkml]   [2008]   [Mar]   [11]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    Date
    From
    SubjectRe: [linux-pm] [PATCH] cpuidle: avoid singing capacitors
    I had a sudden surge of inspiration and decided to follow up on this
    one a bit:

    >
    > 5. Second core
    >
    > Disabling the second core makes the noise go away. This might be a subset of 1., as I've been told that a stopped core enters C1.
    >

    I have now found a very hacky workaround that is slightly better than
    disabling C3 altogether; making C3 exclusive to one core at a time. It
    seems to kill the noise and the system now spends 50% in C3, instead of
    0%.

    I read somewhere that the Intel Duo:s have an extra low power mode that
    is entered if both cores are suspended at the same time (disabling the
    shared cache or something like that I guess). So perhaps that mode is
    the culprit. I'm hoping there's a way to disable just that feature. Do
    any of you know a way? Venkatesh perhaps?

    Here's the patch I'm currently running at least:

    diff --git a/drivers/cpuidle/governors/menu.c b/drivers/cpuidle/governors/menu.c
    index 78d77c5..9a859fb 100644
    --- a/drivers/cpuidle/governors/menu.c
    +++ b/drivers/cpuidle/governors/menu.c
    @@ -16,6 +16,8 @@

    #define BREAK_FUZZ 4 /* 4 us */

    +static atomic_t cur_deep_cpu = ATOMIC_INIT(-1);
    +
    struct menu_device {
    int last_state_idx;

    @@ -50,6 +52,13 @@ static int menu_select(struct cpuidle_device *dev)
    break;
    if (s->exit_latency > pm_qos_requirement(PM_QOS_CPU_DMA_LATENCY))
    break;
    +
    + if (s->flags & CPUIDLE_FLAG_DEEP) {
    + rmb();
    + if (atomic_cmpxchg(&cur_deep_cpu, -1, dev->cpu) != -1)
    + break;
    + wmb();
    + }
    }

    data->last_state_idx = i - 1;
    @@ -80,6 +89,11 @@ static void menu_reflect(struct cpuidle_device *dev)
    if (!(target->flags & CPUIDLE_FLAG_TIME_VALID))
    measured_us = USEC_PER_SEC / HZ;

    + if (atomic_read(&cur_deep_cpu) == dev->cpu) {
    + atomic_set(&cur_deep_cpu, -1);
    + wmb();
    + }
    +
    /* Predict time remaining until next break event */
    if (measured_us + BREAK_FUZZ < data->expected_us - target->exit_latency) {
    data->predicted_us = max(measured_us, data->last_measured_us);

    --
    -- Pierre Ossman

    Linux kernel, MMC maintainer http://www.kernel.org
    PulseAudio, core developer http://pulseaudio.org
    rdesktop, core developer http://www.rdesktop.org


    \
     
     \ /
      Last update: 2008-03-11 08:55    [W:4.773 / U:0.648 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site