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SubjectRe: [PATCH 2/4] perf/ftrace: Fix function trace events
On 2017/10/11 15:45, Peter Zijlstra wrote:
> The function-trace<-> perf interface is a tad messed up. Where all
> the other trace<-> perf interfaces use a single trace hook
> registration and use per-cpu RCU based hlist to iterate the events,
> function-trace actually needs multiple hook registrations in order to
> minimize function entry patching when filters are present.
>
> The end result is that we iterate events both on the trace hook and on
> the hlist, which results in reporting events multiple times.
>
> Since function-trace cannot use the regular scheme, fix it the other
> way around, use singleton hlists.
>
> Signed-off-by: Peter Zijlstra (Intel)<peterz@infradead.org>
> ---
> include/linux/trace_events.h | 5 ++
> kernel/trace/trace_event_perf.c | 82 ++++++++++++++++++++++++----------------
> 2 files changed, 55 insertions(+), 32 deletions(-)
>
> --- a/include/linux/trace_events.h
> +++ b/include/linux/trace_events.h
> @@ -173,6 +173,11 @@ enum trace_reg {
> TRACE_REG_PERF_UNREGISTER,
> TRACE_REG_PERF_OPEN,
> TRACE_REG_PERF_CLOSE,
> + /*
> + * These (ADD/DEL) use a 'boolean' return value, where 1 (true) means a
> + * custom action was taken and the default action is not to be
> + * performed.
> + */
> TRACE_REG_PERF_ADD,
> TRACE_REG_PERF_DEL,
> #endif
> --- a/kernel/trace/trace_event_perf.c
> +++ b/kernel/trace/trace_event_perf.c
> @@ -240,27 +240,41 @@ void perf_trace_destroy(struct perf_even
> int perf_trace_add(struct perf_event *p_event, int flags)
> {
> struct trace_event_call *tp_event = p_event->tp_event;
> - struct hlist_head __percpu *pcpu_list;
> - struct hlist_head *list;
>
> - pcpu_list = tp_event->perf_events;
> - if (WARN_ON_ONCE(!pcpu_list))
> - return -EINVAL;
> + /*
> + * If TRACE_REG_PERF_ADD returns false; no custom action was performed
> + * and we need to take the default action of enqueueing our event on
> + * the right per-cpu hlist.
> + */
> + if (!tp_event->class->reg(tp_event, TRACE_REG_PERF_ADD, p_event)) {
> + struct hlist_head __percpu *pcpu_list;
> + struct hlist_head *list;
> +
> + pcpu_list = tp_event->perf_events;
> + if (WARN_ON_ONCE(!pcpu_list))
> + return -EINVAL;
>
> - if (!(flags& PERF_EF_START))
> - p_event->hw.state = PERF_HES_STOPPED;
> + if (!(flags& PERF_EF_START))
> + p_event->hw.state = PERF_HES_STOPPED;

Don't we need to check the flags for ftrace perf_event?
So if we should put this outside the if (!tp_event->class->reg()) ?

>
> - list = this_cpu_ptr(pcpu_list);
> - hlist_add_head_rcu(&p_event->hlist_entry, list);
> + list = this_cpu_ptr(pcpu_list);
> + hlist_add_head_rcu(&p_event->hlist_entry, list);
> + }

Now we don't add perf_event to the pcpu_list, so we also can avoid
to alloc pcpu_list for function tp_event in perf_trace_event_reg().

Thanks.

>
> - return tp_event->class->reg(tp_event, TRACE_REG_PERF_ADD, p_event);
> + return 0;
> }
>
> void perf_trace_del(struct perf_event *p_event, int flags)
> {
> struct trace_event_call *tp_event = p_event->tp_event;
> - hlist_del_rcu(&p_event->hlist_entry);
> - tp_event->class->reg(tp_event, TRACE_REG_PERF_DEL, p_event);
> +
> + /*
> + * If TRACE_REG_PERF_DEL returns false; no custom action was performed
> + * and we need to take the default action of dequeueing our event from
> + * the right per-cpu hlist.
> + */
> + if (!tp_event->class->reg(tp_event, TRACE_REG_PERF_DEL, p_event))
> + hlist_del_rcu(&p_event->hlist_entry);
> }
>
> void *perf_trace_buf_alloc(int size, struct pt_regs **regs, int *rctxp)
> @@ -307,14 +321,24 @@ perf_ftrace_function_call(unsigned long
> struct ftrace_ops *ops, struct pt_regs *pt_regs)
> {
> struct ftrace_entry *entry;
> - struct hlist_head *head;
> + struct perf_event *event;
> + struct hlist_head head;
> struct pt_regs regs;
> int rctx;
>
> - head = this_cpu_ptr(event_function.perf_events);
> - if (hlist_empty(head))
> + if ((unsigned long)ops->private != smp_processor_id())
> return;
>
> + event = container_of(ops, struct perf_event, ftrace_ops);
> +
> + /*
> + * @event->hlist entry is NULL (per INIT_HLIST_NODE), and all
> + * the perf code does is hlist_for_each_entry_rcu(), so we can
> + * get away with simply setting the @head.first pointer in order
> + * to create a singular list.
> + */
> + head.first =&event->hlist_entry;
> +
> #define ENTRY_SIZE (ALIGN(sizeof(struct ftrace_entry) + sizeof(u32), \
> sizeof(u64)) - sizeof(u32))
>
> @@ -330,7 +354,7 @@ perf_ftrace_function_call(unsigned long
> entry->ip = ip;
> entry->parent_ip = parent_ip;
> perf_trace_buf_submit(entry, ENTRY_SIZE, rctx, TRACE_FN,
> - 1,&regs, head, NULL);
> + 1,&regs,&head, NULL);
>
> #undef ENTRY_SIZE
> }
> @@ -339,8 +363,10 @@ static int perf_ftrace_function_register
> {
> struct ftrace_ops *ops =&event->ftrace_ops;
>
> - ops->flags |= FTRACE_OPS_FL_PER_CPU | FTRACE_OPS_FL_RCU;
> - ops->func = perf_ftrace_function_call;
> + ops->flags |= FTRACE_OPS_FL_RCU;
> + ops->func = perf_ftrace_function_call;
> + ops->private = (void *)(unsigned long)nr_cpu_ids;
> +
> return register_ftrace_function(ops);
> }
>
> @@ -352,19 +378,11 @@ static int perf_ftrace_function_unregist
> return ret;
> }
>
> -static void perf_ftrace_function_enable(struct perf_event *event)
> -{
> - ftrace_function_local_enable(&event->ftrace_ops);
> -}
> -
> -static void perf_ftrace_function_disable(struct perf_event *event)
> -{
> - ftrace_function_local_disable(&event->ftrace_ops);
> -}
> -
> int perf_ftrace_event_register(struct trace_event_call *call,
> enum trace_reg type, void *data)
> {
> + struct perf_event *event = data;
> +
> switch (type) {
> case TRACE_REG_REGISTER:
> case TRACE_REG_UNREGISTER:
> @@ -377,11 +395,11 @@ int perf_ftrace_event_register(struct tr
> case TRACE_REG_PERF_CLOSE:
> return perf_ftrace_function_unregister(data);
> case TRACE_REG_PERF_ADD:
> - perf_ftrace_function_enable(data);
> - return 0;
> + event->ftrace_ops.private = (void *)(unsigned long)smp_processor_id();
> + return 1;
> case TRACE_REG_PERF_DEL:
> - perf_ftrace_function_disable(data);
> - return 0;
> + event->ftrace_ops.private = (void *)(unsigned long)nr_cpu_ids;
> + return 1;
> }
>
> return -EINVAL;
>
>
>
> .
>


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