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    SubjectRe: [PATCH v3 00/10] Add tegra30 support for secondary cores
    On Wed, Feb 15, 2012 at 10:27:43PM +0100, Stephen Warren wrote:
    > Peter De Schrijver wrote at Thursday, February 09, 2012 4:48 PM:
    > > This patchset introduces support for secondary cores on tegra30. It also
    > > introduces some functions for the flowcontroller and adds basic support for
    > > tegra30 powerdomains.
    >
    > The code looks fine to me. I do notice the following when running
    > "shutdown -h now":
    >
    > [ 27.762124] SMP: failed to stop secondary CPUs
    >
    > So, this patch series makes the secondary cores boot OK, but not shut
    > down it appears. Is that expected? It's probably something we can fix
    > with a following on patch rather than re-spinning this series though?
    >

    I spent some more time looking at this. It appears that nr_online_cpus isn't
    always updated properly. I added an extra pr_warn() when the failure happens
    and I got:

    [ 22.369815] Restarting system.
    [ 23.506792] SMP: failed to stop secondary CPUs
    [ 23.511535] running on CPU: 3, still online: 2, mask: 8

    I also did some function tracing and all CPUs besides the one initiating the
    halt reach platform_cpu_kill() about 50us after sending the IPIs to stop them.
    The set_cpu_online() call in ipi_cpu_stop() should update nr_online_cpus, but
    somehow this doesn't always happen. Any insight on what might be going on?

    Instrumentation patch attached.

    Cheers,

    Peter.

    From d871feda574bd9f626f175be403cabd308ca18c0 Mon Sep 17 00:00:00 2001
    From: Peter De Schrijver <pdeschrijver@nvidia.com>
    Date: Wed, 29 Feb 2012 17:37:27 +0200
    Subject: [PATCH] ARM: debugging smp_send_stop
    X-NVConfidentiality: public

    Change-Id: Ia4f33b054f2eccf173a3d977686e1577e2146b92
    ---
    arch/arm/kernel/smp.c | 7 ++++++-
    1 files changed, 6 insertions(+), 1 deletions(-)

    diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
    index 3e43c5f..e0e5eea 100644
    --- a/arch/arm/kernel/smp.c
    +++ b/arch/arm/kernel/smp.c
    @@ -570,6 +570,7 @@ void smp_send_reschedule(int cpu)
    void smp_send_stop(void)
    {
    unsigned long timeout;
    + int cpu = smp_processor_id();

    if (num_online_cpus() > 1) {
    cpumask_t mask = cpu_online_map;
    @@ -583,8 +584,12 @@ void smp_send_stop(void)
    while (num_online_cpus() > 1 && timeout--)
    udelay(1);

    - if (num_online_cpus() > 1)
    + if (num_online_cpus() > 1) {
    + char cpu_mask[10];
    pr_warning("SMP: failed to stop secondary CPUs\n");
    + cpumask_scnprintf(cpu_mask, sizeof(cpu_mask), cpu_online_mask);
    + pr_warn("running on CPU: %d, still online: %d, mask: %s\n", cpu, num_online_cpus(), cpu_mask);
    + }
    }

    /*
    --
    1.7.7.rc0.72.g4b5ea.dirty
    \
     
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