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Date: Thu, 06 Feb 2014 09:38:33 +0800
From: "Yan, Zheng" <zheng.z.yan@...el.com>
To: Stephane Eranian <eranian@...gle.com>
CC: LKML <linux-kernel@...r.kernel.org>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>,
Ingo Molnar <mingo@...nel.org>,
Arnaldo Carvalho de Melo <acme@...radead.org>,
Andi Kleen <andi@...stfloor.org>
Subject: Re: [PATCH 02/14] perf, core: introduce pmu context switch callback
On 02/06/2014 12:01 AM, Stephane Eranian wrote:
> On Fri, Jan 3, 2014 at 6:47 AM, Yan, Zheng <zheng.z.yan@...el.com> 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@...el.com>
>> ---
>> 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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