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SubjectRe: [PATCH] perf_events: fix bug in AMD per-cpu initialization
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On Tue, Mar 23, 2010 at 3:11 PM, Peter Zijlstra <peterz@infradead.org> wrote:
> On Thu, 2010-03-18 at 01:33 +0100, Stephane Eranian wrote:
>> On Thu, Mar 18, 2010 at 12:47 AM, Peter Zijlstra <peterz@infradead.org> wrote:
>> > On Wed, 2010-03-17 at 10:40 +0200, Stephane Eranian wrote:
>> >>       On AMD processors, we need to allocate a data structure per Northbridge
>> >>       to handle certain events.
>> >>
>> >>       On CPU initialization, we need to query the Northbridge id and check
>> >>       whether the structure is already allocated or not. We use the
>> >>       amd_get_nb_id() function to request the Northbridge identification.
>> >>
>> >>       The recent cleanup of the CPU online/offline initialization introduced
>> >>       a bug. AMD cpu initialization is invoked on CPU_UP_PREPARE callback.
>> >>       This is before the CPU Northbridge id is calculated. Therefore no
>> >>       processor had a Northbridge structure allocated except the boot
>> >>       processor. That was causing bogus NB event scheduling.
>> >>
>> >>       This patch uses the CPU_ONLINE callback to initialize the AMD
>> >>       Northbridge structure. This way amd_get_nb_id() returns valid
>> >>       information.
>> >>
>> >>       The x86_cpu_up() callback was added. Could not call it cpu_online
>> >>       because of existing macro.
>> >>
>> >>       Signed-off-by: Stephane Eranian <eranian@google.com>
>> >
>> >
>> > No, ONLINE is not exposed for a good reason, its always wrong.
>> >
>> > Use prepare to allocate data, and starting to initialize stuff on the
>> > cpu proper once its up. Online is after the cpu is up and running and we
>> > are already scheduling stuff on it so its too late to initialize things.
>> >
>> >
>> I can't because amd_get_nb_id() returns garbage for the CPU
>> when you call from CPU_STARTING. So looks like initialization
>> of cpu_llc_id needs to be moved way earlier. I don't want to have
>> to duplicate that code.
>
> Crap, you're right, either notify_cpu_starting() is done too early or
> smp_store_cpu_info() is done too late.
>
> Since smp_store_cpu_info() relies on the result of calibrate_delay() we
> can't easily change that order, but since there really isn't any other
> CPU_STARTING user in tree (I appear to have created the first?!) we can
> easily move that notifier thing later.
>
What's the point of CPU_ONLINE vs. CPU_STARTING if you're saying the
former is never right? Why not move CPU_ONLINE to the right place and drop
CPU_STARTING?



> (What's up with that IRQ-enable over calibrate_delay(), can't we simply
> enable the NMI watchdog later?)
>
> So I guess something like the below should work:
>
> ---
> arch/x86/kernel/smpboot.c |    4 ++--
> 1 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
> index 06d98ae..6808b93 100644
> --- a/arch/x86/kernel/smpboot.c
> +++ b/arch/x86/kernel/smpboot.c
> @@ -242,8 +242,6 @@ static void __cpuinit smp_callin(void)
> end_local_APIC_setup();
> map_cpu_to_logical_apicid();
>
> - notify_cpu_starting(cpuid);
> -
> /*
> * Need to setup vector mappings before we enable interrupts.
> */
> @@ -264,6 +262,8 @@ static void __cpuinit smp_callin(void)
> */
> smp_store_cpu_info(cpuid);
>
> + notify_cpu_starting(cpuid);
> +
> /*
> * Allow the master to continue.
> */
>
>
> Which then allows us to write something like:
>
> ---
>
>  arch/x86/kernel/cpu/perf_event.c     |    8 ++-
>  arch/x86/kernel/cpu/perf_event_amd.c |   69 ++++++++++++++++++---------------
>  2 files changed, 43 insertions(+), 34 deletions(-)
>
> diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
> index f571f51..4db6eaf 100644
> --- a/arch/x86/kernel/cpu/perf_event.c
> +++ b/arch/x86/kernel/cpu/perf_event.c
> @@ -209,7 +209,7 @@ struct x86_pmu {
>        struct event_constraint *event_constraints;
>        void            (*quirks)(void);
>
> -       void            (*cpu_prepare)(int cpu);
> +       int             (*cpu_prepare)(int cpu);
>        void            (*cpu_starting)(int cpu);
>        void            (*cpu_dying)(int cpu);
>        void            (*cpu_dead)(int cpu);
> @@ -1330,11 +1330,12 @@ static int __cpuinit
>  x86_pmu_notifier(struct notifier_block *self, unsigned long action, void *hcpu)
>  {
>        unsigned int cpu = (long)hcpu;
> +       int ret = NOTIFY_OK;
>
>        switch (action & ~CPU_TASKS_FROZEN) {
>        case CPU_UP_PREPARE:
>                if (x86_pmu.cpu_prepare)
> -                       x86_pmu.cpu_prepare(cpu);
> +                       ret = x86_pmu.cpu_prepare(cpu);
>                break;
>
>        case CPU_STARTING:
> @@ -1347,6 +1348,7 @@ x86_pmu_notifier(struct notifier_block *self, unsigned long action, void *hcpu)
>                        x86_pmu.cpu_dying(cpu);
>                break;
>
> +       case CPU_UP_CANCELED:
>        case CPU_DEAD:
>                if (x86_pmu.cpu_dead)
>                        x86_pmu.cpu_dead(cpu);
> @@ -1356,7 +1358,7 @@ x86_pmu_notifier(struct notifier_block *self, unsigned long action, void *hcpu)
>                break;
>        }
>
> -       return NOTIFY_OK;
> +       return ret;
>  }
>
>  static void __init pmu_check_apic(void)
> diff --git a/arch/x86/kernel/cpu/perf_event_amd.c b/arch/x86/kernel/cpu/perf_event_amd.c
> index bdd8f8e..b78c6c5 100644
> --- a/arch/x86/kernel/cpu/perf_event_amd.c
> +++ b/arch/x86/kernel/cpu/perf_event_amd.c
> @@ -293,51 +293,55 @@ static struct amd_nb *amd_alloc_nb(int cpu, int nb_id)
>        return nb;
>  }
>
> -static void amd_pmu_cpu_online(int cpu)
> +static int amd_pmu_cpu_prepare(int cpu)
>  {
> -       struct cpu_hw_events *cpu1, *cpu2;
> -       struct amd_nb *nb = NULL;
> +       struct cpu_hw_events *cpuc = &per_cpu(cpu_hw_events, cpu);
> +
> +       WARN_ON_ONCE(cpuc->amd_nb);
> +
> +       if (boot_cpu_data.x86_max_cores < 2)
> +               return NOTIFY_OK;
> +
> +       cpuc->amd_nb = amd_alloc_nb(cpu, -1);
> +       if (!cpuc->amd_nb)
> +               return NOTIFY_BAD;
> +
> +       return NOTIFY_OK;
> +}
> +
> +static void amd_pmu_cpu_starting(int cpu)
> +{
> +       struct cpu_hw_events *cpuc = &per_cpu(cpu_hw_events, cpu);
> +       struct amd_nb *nb;
>        int i, nb_id;
>
>        if (boot_cpu_data.x86_max_cores < 2)
>                return;
>
> -       /*
> -        * function may be called too early in the
> -        * boot process, in which case nb_id is bogus
> -        */
>        nb_id = amd_get_nb_id(cpu);
> -       if (nb_id == BAD_APICID)
> -               return;
> -
> -       cpu1 = &per_cpu(cpu_hw_events, cpu);
> -       cpu1->amd_nb = NULL;
> +       WARN_ON_ONCE(nb_id == BAD_APICID);
>
>        raw_spin_lock(&amd_nb_lock);
>
>        for_each_online_cpu(i) {
> -               cpu2 = &per_cpu(cpu_hw_events, i);
> -               nb = cpu2->amd_nb;
> -               if (!nb)
> +               nb = per_cpu(cpu_hw_events, i).amd_nb;
> +               if (WARN_ON_ONCE(!nb))
>                        continue;
> -               if (nb->nb_id == nb_id)
> -                       goto found;
> -       }
>
> -       nb = amd_alloc_nb(cpu, nb_id);
> -       if (!nb) {
> -               pr_err("perf_events: failed NB allocation for CPU%d\n", cpu);
> -               raw_spin_unlock(&amd_nb_lock);
> -               return;
> +               if (nb->nb_id == nb_id) {
> +                       kfree(cpuc->amd_nb);
> +                       cpuc->amd_nb = nb;
> +                       break;
> +               }
>        }
> -found:
> -       nb->refcnt++;
> -       cpu1->amd_nb = nb;
> +
> +       cpuc->amd_nb->nb_id = nb_id;
> +       cpuc->amd_nb->refcnt++;
>
>        raw_spin_unlock(&amd_nb_lock);
>  }
>
> -static void amd_pmu_cpu_offline(int cpu)
> +static void amd_pmu_cpu_dead(int cpu)
>  {
>        struct cpu_hw_events *cpuhw;
>
> @@ -349,8 +353,10 @@ static void amd_pmu_cpu_offline(int cpu)
>        raw_spin_lock(&amd_nb_lock);
>
>        if (cpuhw->amd_nb) {
> -               if (--cpuhw->amd_nb->refcnt == 0)
> -                       kfree(cpuhw->amd_nb);
> +               struct amd_nb *nb = cpuhw->amd_nb;
> +
> +               if (nb->nb_id == -1 || --nb->refcnt == 0)
> +                       kfree(nb);
>
>                cpuhw->amd_nb = NULL;
>        }
> @@ -381,8 +387,9 @@ static __initconst struct x86_pmu amd_pmu = {
>        .get_event_constraints  = amd_get_event_constraints,
>        .put_event_constraints  = amd_put_event_constraints,
>
> -       .cpu_prepare            = amd_pmu_cpu_online,
> -       .cpu_dead               = amd_pmu_cpu_offline,
> +       .cpu_prepare            = amd_pmu_cpu_prepare,
> +       .cpu_starting           = amd_pmu_cpu_starting,
> +       .cpu_dead               = amd_pmu_cpu_dead,
>  };
>
>  static __init int amd_pmu_init(void)
>
>



--
Stephane Eranian  | EMEA Software Engineering
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