Re: [PATCH 02/14] perf, core: introduce pmu context switch callback

[Yan, Zheng]

On 02/06/2014 12:01 AM, Stephane Eranian wrote:
> On Fri, Jan 3, 2014 at 6:47 AM, Yan, Zheng <zheng.z.yan@xxxxxxxxx> wrote:
>> The callback is invoked when process is scheduled in or out. It
>> provides mechanism for later patches to save/store the LBR stack.
>> It can also replace the flush branch stack callback.
>>
> I think you need to say this callback may be invoked on context switches
> with per-thread events attached. As far I understand, the callback cannot
> be invoked for system-wide events.

It's also invoked when there is only system-wide event. (the flush branch stack case)

Regards
Yan, Zheng


> 
>> To avoid unnecessary overhead, the callback is enabled dynamically
>>
>> Signed-off-by: Yan, Zheng <zheng.z.yan@xxxxxxxxx>
>> ---
>>  arch/x86/kernel/cpu/perf_event.c |  7 +++++
>>  arch/x86/kernel/cpu/perf_event.h |  4 +++
>>  include/linux/perf_event.h       |  8 ++++++
>>  kernel/events/core.c             | 60 +++++++++++++++++++++++++++++++++++++++-
>>  4 files changed, 78 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
>> index 8e13293..6703d17 100644
>> --- a/arch/x86/kernel/cpu/perf_event.c
>> +++ b/arch/x86/kernel/cpu/perf_event.c
>> @@ -1846,6 +1846,12 @@ static const struct attribute_group *x86_pmu_attr_groups[] = {
>>         NULL,
>>  };
>>
>> +static void x86_pmu_sched_task(struct perf_event_context *ctx, bool sched_in)
>> +{
>> +       if (x86_pmu.sched_task)
>> +               x86_pmu.sched_task(ctx, sched_in);
>> +}
>> +
>>  static void x86_pmu_flush_branch_stack(void)
>>  {
>>         if (x86_pmu.flush_branch_stack)
>> @@ -1879,6 +1885,7 @@ static struct pmu pmu = {
>>
>>         .event_idx              = x86_pmu_event_idx,
>>         .flush_branch_stack     = x86_pmu_flush_branch_stack,
>> +       .sched_task             = x86_pmu_sched_task,
>>  };
>>
>>  void arch_perf_update_userpage(struct perf_event_mmap_page *userpg, u64 now)
>> diff --git a/arch/x86/kernel/cpu/perf_event.h b/arch/x86/kernel/cpu/perf_event.h
>> index 745f6fb..3fdb751 100644
>> --- a/arch/x86/kernel/cpu/perf_event.h
>> +++ b/arch/x86/kernel/cpu/perf_event.h
>> @@ -417,6 +417,8 @@ struct x86_pmu {
>>
>>         void            (*check_microcode)(void);
>>         void            (*flush_branch_stack)(void);
>> +       void            (*sched_task)(struct perf_event_context *ctx,
>> +                                     bool sched_in);
>>
>>         /*
>>          * Intel Arch Perfmon v2+
>> @@ -675,6 +677,8 @@ void intel_pmu_pebs_disable_all(void);
>>
>>  void intel_ds_init(void);
>>
>> +void intel_pmu_lbr_sched_task(struct perf_event_context *ctx, bool sched_in);
>> +
> There is no mention of this function anywhere else. Should not be here.
> 
>>  void intel_pmu_lbr_reset(void);
>>
>>  void intel_pmu_lbr_enable(struct perf_event *event);
>> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
>> index 8f4a70f..6a3e603 100644
>> --- a/include/linux/perf_event.h
>> +++ b/include/linux/perf_event.h
>> @@ -251,6 +251,12 @@ struct pmu {
>>          * flush branch stack on context-switches (needed in cpu-wide mode)
>>          */
>>         void (*flush_branch_stack)      (void);
>> +
>> +       /*
>> +        * PMU callback for context-switches. optional
>> +        */
>> +       void (*sched_task)              (struct perf_event_context *ctx,
>> +                                        bool sched_in);
>>  };
>>
>>  /**
>> @@ -546,6 +552,8 @@ extern void perf_event_delayed_put(struct task_struct *task);
>>  extern void perf_event_print_debug(void);
>>  extern void perf_pmu_disable(struct pmu *pmu);
>>  extern void perf_pmu_enable(struct pmu *pmu);
>> +extern void perf_sched_cb_disable(struct pmu *pmu);
>> +extern void perf_sched_cb_enable(struct pmu *pmu);
>>  extern int perf_event_task_disable(void);
>>  extern int perf_event_task_enable(void);
>>  extern int perf_event_refresh(struct perf_event *event, int refresh);
>> diff --git a/kernel/events/core.c b/kernel/events/core.c
>> index 89d34f9..d110a23 100644
>> --- a/kernel/events/core.c
>> +++ b/kernel/events/core.c
>> @@ -141,6 +141,7 @@ enum event_type_t {
>>  struct static_key_deferred perf_sched_events __read_mostly;
>>  static DEFINE_PER_CPU(atomic_t, perf_cgroup_events);
>>  static DEFINE_PER_CPU(atomic_t, perf_branch_stack_events);
>> +static DEFINE_PER_CPU(int, perf_sched_cb_usages);
>>
>>  static atomic_t nr_mmap_events __read_mostly;
>>  static atomic_t nr_comm_events __read_mostly;
>> @@ -150,6 +151,7 @@ static atomic_t nr_freq_events __read_mostly;
>>  static LIST_HEAD(pmus);
>>  static DEFINE_MUTEX(pmus_lock);
>>  static struct srcu_struct pmus_srcu;
>> +static struct idr pmu_idr;
>>
>>  /*
>>   * perf event paranoia level:
>> @@ -2327,6 +2329,57 @@ unlock:
>>         }
>>  }
>>
>> +void perf_sched_cb_disable(struct pmu *pmu)
>> +{
>> +       __get_cpu_var(perf_sched_cb_usages)--;
>> +}
>> +
>> +void perf_sched_cb_enable(struct pmu *pmu)
>> +{
>> +       __get_cpu_var(perf_sched_cb_usages)++;
>> +}
>> +
> I think you want to use jump_labels instead of this to make
> the callback optional. This is already used all over the place
> in the generic code.
> 
>> +/*
>> + * This function provides the context switch callback to the lower code
>> + * layer. It is invoked ONLY when the context switch callback is enabled.
>> + */
>> +static void perf_pmu_sched_task(struct task_struct *prev,
>> +                               struct task_struct *next,
>> +                               bool sched_in)
>> +{
>> +       struct perf_cpu_context *cpuctx;
>> +       struct pmu *pmu;
>> +       unsigned long flags;
>> +
>> +       if (prev == next)
>> +               return;
>> +
>> +       local_irq_save(flags);
>> +
>> +       rcu_read_lock();
>> +
>> +       pmu = idr_find(&pmu_idr, PERF_TYPE_RAW);
>> +
>> +       if (pmu && pmu->sched_task) {
>> +               cpuctx = this_cpu_ptr(pmu->pmu_cpu_context);
>> +               pmu = cpuctx->ctx.pmu;
>> +
>> +               perf_ctx_lock(cpuctx, cpuctx->task_ctx);
>> +
>> +               perf_pmu_disable(pmu);
>> +
>> +               pmu->sched_task(cpuctx->task_ctx, sched_in);
>> +
>> +               perf_pmu_enable(pmu);
>> +
>> +               perf_ctx_unlock(cpuctx, cpuctx->task_ctx);
>> +       }
>> +
>> +       rcu_read_unlock();
>> +
>> +       local_irq_restore(flags);
>> +}
>> +
>>  #define for_each_task_context_nr(ctxn)                                 \
>>         for ((ctxn) = 0; (ctxn) < perf_nr_task_contexts; (ctxn)++)
>>
>> @@ -2346,6 +2399,9 @@ void __perf_event_task_sched_out(struct task_struct *task,
>>  {
>>         int ctxn;
>>
>> +       if (__get_cpu_var(perf_sched_cb_usages))
>> +               perf_pmu_sched_task(task, next, false);
>> +
>>         for_each_task_context_nr(ctxn)
>>                 perf_event_context_sched_out(task, ctxn, next);
>>
>> @@ -2605,6 +2661,9 @@ void __perf_event_task_sched_in(struct task_struct *prev,
>>         /* check for system-wide branch_stack events */
>>         if (atomic_read(&__get_cpu_var(perf_branch_stack_events)))
>>                 perf_branch_stack_sched_in(prev, task);
>> +
>> +       if (__get_cpu_var(perf_sched_cb_usages))
>> +               perf_pmu_sched_task(prev, task, true);
>>  }
>>
>>  static u64 perf_calculate_period(struct perf_event *event, u64 nsec, u64 count)
>> @@ -6326,7 +6385,6 @@ static void free_pmu_context(struct pmu *pmu)
>>  out:
>>         mutex_unlock(&pmus_lock);
>>  }
>> -static struct idr pmu_idr;
>>
>>  static ssize_t
>>  type_show(struct device *dev, struct device_attribute *attr, char *page)
>> --
>> 1.8.4.2
>>

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