Re: [PATCH v6 2/3] binder: add trace at free transaction.

[Todd Kjos <tkjos@google.com>]

On Mon, Jul 27, 2020 at 8:28 PM Frankie Chang
<Frankie.Chang@mediatek.com> wrote:
>
> From: "Frankie.Chang" <Frankie.Chang@mediatek.com>
>
> Since the original trace_binder_transaction_received cannot
> precisely present the real finished time of transaction, adding a
> trace_binder_txn_latency_free at the point of free transaction
> may be more close to it.
>
> Signed-off-by: Frankie.Chang <Frankie.Chang@mediatek.com>
> ---
>  drivers/android/binder.c       |    6 ++++++
>  drivers/android/binder_trace.h |   27 +++++++++++++++++++++++++++
>  2 files changed, 33 insertions(+)
>
> diff --git a/drivers/android/binder.c b/drivers/android/binder.c
> index 2df146f..1e6fc40 100644
> --- a/drivers/android/binder.c
> +++ b/drivers/android/binder.c
> @@ -1522,6 +1522,9 @@ static void binder_free_transaction(struct binder_transaction *t)
>          * If the transaction has no target_proc, then
>          * t->buffer->transaction has already been cleared.
>          */
> +       spin_lock(&t->lock);
> +       trace_binder_txn_latency_free(t);
> +       spin_unlock(&t->lock);

Hmm. I don't prefer taking the lock just to call a trace. It doesn't
make clear why the lock has to be taken. I'd prefer something like:

if (trace_binder_txn_latency_free_enabled()) {
  int to_proc, to_thread;

  spin_lock(&t->lock);
  to_proc = t->to_proc ? t->to_proc->pid : 0;
  to_thread = t->to_thread ? t->to_thread->pid : 0;
  spin_unlock(&t->lock);
  trace_binder_txn_latency_free(t, to_proc, to_pid);
}

And then the trace would use the passed-in values instead of accessing
via t->to_proc/to_thread.

>         binder_free_txn_fixups(t);
>         kfree(t);
>         binder_stats_deleted(BINDER_STAT_TRANSACTION);
> @@ -3093,6 +3096,9 @@ static void binder_transaction(struct binder_proc *proc,
>         kfree(tcomplete);
>         binder_stats_deleted(BINDER_STAT_TRANSACTION_COMPLETE);
>  err_alloc_tcomplete_failed:
> +       spin_lock(&t->lock);
> +       trace_binder_txn_latency_free(t);
> +       spin_unlock(&t->lock);
>         kfree(t);
>         binder_stats_deleted(BINDER_STAT_TRANSACTION);
>  err_alloc_t_failed:
> diff --git a/drivers/android/binder_trace.h b/drivers/android/binder_trace.h
> index 6731c3c..8ac87d1 100644
> --- a/drivers/android/binder_trace.h
> +++ b/drivers/android/binder_trace.h
> @@ -95,6 +95,33 @@
>                   __entry->thread_todo)
>  );
>
> +TRACE_EVENT(binder_txn_latency_free,
> +       TP_PROTO(struct binder_transaction *t),
> +       TP_ARGS(t),
> +       TP_STRUCT__entry(
> +               __field(int, debug_id)
> +               __field(int, from_proc)
> +               __field(int, from_thread)
> +               __field(int, to_proc)
> +               __field(int, to_thread)
> +               __field(unsigned int, code)
> +               __field(unsigned int, flags)
> +       ),
> +       TP_fast_assign(
> +               __entry->debug_id = t->debug_id;
> +               __entry->from_proc = t->from ? t->from->proc->pid : 0;
> +               __entry->from_thread = t->from ? t->from->pid : 0;
> +               __entry->to_proc = t->to_proc ? t->to_proc->pid : 0;
> +               __entry->to_thread = t->to_thread ? t->to_thread->pid : 0;
> +               __entry->code = t->code;
> +               __entry->flags = t->flags;
> +       ),
> +       TP_printk("transaction=%d from %d:%d to %d:%d flags=0x%x code=0x%x",
> +                 __entry->debug_id, __entry->from_proc, __entry->from_thread,
> +                 __entry->to_proc, __entry->to_thread, __entry->code,
> +                 __entry->flags)
> +);
> +
>  TRACE_EVENT(binder_transaction,
>         TP_PROTO(bool reply, struct binder_transaction *t,
>                  struct binder_node *target_node),
> --
> 1.7.9.5