On Wed, 15 Mar 2017 23:20:30 -0400
Steven Rostedt <rost...@goodmis.org> wrote:
> > It is used in lots of places outside trace_handle_return, so that would
> > give far less savings.
Actually, I think you'll probably have *more* savings inlining
trace_handle_return() than trace_seq_has_overflowed(). Why?
Think about it now before looking at the answer below.
> > include/linux/trace_events.h:143: return trace_seq_has_overflowed(s)
> > ?
>
> Every thing below is negligible. The above which is called in
> trace_handle_return() is your problem.
>
> Let me explain it to you.
>
> The above is part of the TRACE_EVENT() logic. It is duplicated for
> *every* tracepoint in the system.
>
> Looking at a current kernel:
>
> # ls /debug/tracing/events/*/*/enable | wc -l
> 1267
>
> There's 1267 events. That means the function trace_handle_return() is
> called 1267 times! THAT IS THE PROBLEM!!!!
>
> Look at include/trace/trace_events.h for
>
> trace_raw_output_##call()
>
> That's the macro that creates over a thousand functions calling
> trace_handle_return().
>
trace_handle_return() is called 1267 times. If you out of line that
function, not only do you save the compares, you also save the
condition too! That could be a jump as well.
static inline enum print_line_t trace_handle_return(struct trace_seq *s)
{
return trace_seq_has_overflowed(s) ?
TRACE_TYPE_PARTIAL_LINE : TRACE_TYPE_HANDLED;
}
The above is called 1267 times. If you move out of line
trace_seq_has_overflowed() you only saved the
s->full || s->seq->len > s->seq->size
part from being duplicated.
But if you out of line trace_handle_return, you move out
s->full || s->seq->len > s->seq->size ?
TRACE_TYPE_PARTIAL_LINE :
TRACE_TYPE-HANDLED
1267 times as well.
Try it. It may surprise you.
-- Steve
