Re: [PATCH 0/11] LTTng-core (basic tracing infrastructure) 0.5.108

[Ingo Molnar]

* Nicholas Miell <nmiell@xxxxxxxxxxx> wrote:

> You're going to want to be able to trace every function in the kernel, 
> which means they'd all need a __trace -- and in that case, a 
> -fpad-functions-for-tracing gcc option would make more sense then 
> per-function attributes.

the __trace attribute would be a _specific_ replacement for a _specific_ 
static markup at the entry of a function. So no, we would not want to 
add __trace to _every_ function in the kernel: only those which get 
commonly traced. And note that SystemTap can trace the rest too, just 
with slighly higher overhead.

In that sense __trace is not an enabling infrastructure, it's a 
performance tuning infrastructure.

> The option could also insert NOPs before RETs, not just before the 
> prologue so that function returns are equally easy to trace. (It might 
> also inhibit tail calls, assuming being able to trace all function 
> returns is more important than that optimization.)

yeah. __trace_entry and __trace_exit [or both] attributes. Makes sense.

> And SystemTap can already hook into sock_sendmsg() (or any other 
> function) and examine it's arguments -- all of this GCC extension talk 
> is just performance enhancement.

yes, yes, yes, exactly!!! Finally someone reads my mails and understands 
my points. There's hope! ;)

	Ingo
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