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

Ingo Molnar
2009-04-17T19:46:41Z

* 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.

Ingo