Re: [PATCH 1/4] tracing: move __DO_TRACE out of line

Steven Rostedt
2009-04-17T19:58:13Z

On Fri, 17 Apr 2009, Ingo Molnar wrote:

>
> * Jeremy Fitzhardinge <jeremy@goop.org> wrote:
>
> > Taking __do_trace_sched_switch out of lines inserts this into the
> > hot path (6 instructions, 31 bytes):
> >
> > cmpl $0, __tracepoint_sched_switch+8(%rip) #, __tracepoint_sched_switch.state
> > je .L1748 #,
> > movq -136(%rbp), %rdx # next,
> > movq -144(%rbp), %rsi # prev,
> > movq %rbx, %rdi # rq,
> > call __do_trace_sched_switch #
> > .L1748:
>
> Hm, why isnt this off-line in the function? It's marked unlikely(),
> isnt it?
>
> also, did you investigate the effect on the _instrumented_ function
> itself? (i.e. the non-tracing related bits) A function call clobbers
> various registers and creates pressure on gcc to shuffle registers
> around.

I doubt it will make much difference. The inline version stil has the
function call to the trace point handler.

-- Steve