----- Original Message -----
> From: "Steven Rostedt" <rost...@goodmis.org>
> To: "Thomas Gleixner" <t...@linutronix.de>
> Cc: "LKML" <linux-kernel@vger.kernel.org>, "Jiang Liu"
> <jiang....@linux.intel.com>, x...@kernel.org, "Linus Torvalds"
> <torva...@linux-foundation.org>, "Andrew Morton" <a...@linux-foundation.org>,
> "Bjorn Helgaas" <bhelg...@google.com>,
> "Tony Luck" <tony.l...@intel.com>, "Borislav Petkov" <b...@alien8.de>, "Joerg
> Roedel" <j...@8bytes.org>, "Marc
> Zyngier" <marc.zyng...@arm.com>, "Yinghai Lu" <ying...@kernel.org>, "Alex
> Williamson" <alex.william...@redhat.com>,
> "Mathieu Desnoyers" <mathieu.desnoy...@efficios.com>, "Frederic Weisbecker"
> <fweis...@gmail.com>
> Sent: Monday, December 15, 2014 10:52:01 AM
> Subject: Re: Status of tip/x86/apic
>
[...]
> >
> > I think the above can be solved, so we need to agree on a proper
> > set of tracepoints. I came up with the following list:
> >
> > - trace_irqdomain_create(domain->id, domain->name, ...)
>
> Is that suppose to be a variable number of args? Tracepoints do not
> support a variable length number of args passed in. I guess we could
> add that, but it wont be for this merge window.
>
> I've added Mathieu and Frederic to the Cc list here.
Hi Steven,
Let's wait and see if it's really required first.
FWIW, at the user-space level in LTTng-UST, we have two distinct ways to
do static instrumentation:
* tracepoint(): similar to those within the Linux kernel, except that the
tracepoint is wrapped in a define, so rather than calling:
trace_foo(arg1, arg2);
users call:
tracepoint(foo, arg1, arg2);
Which allows skipping over evaluation of "arg1" and "arg2"
even if they have side-effects when the tracepoint is
disabled.
* tracef(): I also added a "tracef()" macro, provides a programmer interface
very similar to printf(), but prints the pretty-printed into the
trace buffers. It can be enabled dynamically similarly to
tracepoints,
but does not have per-site event names attached. They are either
all
enabled or disabled, and meant mainly for adding temporary
debugging
trace statements.
So far, the feedback I got from end users seemed to split static
instrumentation use-cases in two major categories:
1) Instrumentation added into the code base, well structured (tracepoints),
meant to be deployed with the application for in-production use.
They need to be low-overhead,
2) Very quick (and dirty) instrumentation, meant for one-off use while
in development. IOW, a replacement to printf(), with which people are
already familiar. Low-overhead still matters, but not as much as it does
for (1).
This is why we only implemented var arg support in tracef() so far.
>
> If we do support this (and if it is needed) we could make it use the
> bprintf() infrastructure. It already supports just saving a format and
> args directly to the the buffer, and a way to print them again.
Happy new year :)
Thanks,
Mathieu
--
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com
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