Messages in this thread | | | Subject | Re: [RFC][PATCH 2/3] perf: Take a hot regs snapshot for trace events | From | Steven Rostedt <> | Date | Thu, 04 Mar 2010 10:16:41 -0500 |
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On Thu, 2010-03-04 at 12:25 +0100, Ingo Molnar wrote: > * Peter Zijlstra <peterz@infradead.org> wrote: > > > On Wed, 2010-03-03 at 12:07 -0500, Steven Rostedt wrote: > > > oops, my bad :-), I thought this was in the x86 arch directory. For the > > > University, I was helping them with adding trace points for page faults > > > when I came across this in arch/x86/mm/fault.c: > > > > > > perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, 0, regs, address); > > > > > > > > > This is what I actually was wondering about. Why is it a "perf only" trace > > > point instead of a TRACE_EVENT()? > > > > Because I wanted to make perf usable without having to rely on funny > > tracepoints. That is, I am less worried about committing software counters > > to ABI than I am about TRACE_EVENT(), which still gives me a terribly > > uncomfortable feeling. > > I'd still like a much less error-prone and work-intense way of doing it. > > I'd suggest we simply add a TRACE_EVENT_ABI() for such cases, where we really > want to expose a tracepoint to tooling, programmatically. Maybe even change > the usage sites to trace_foo_ABI(), to make it really clear and to make people > aware of the consequences.
Would this still be available as a normal trace event?
> > > Also, building with all CONFIG_TRACE_*=n will still yield a usable perf, > > which is something the embedded people might fancy, all that TRACE stuff > > adds lots of code. > > Not a real issue i suspect when you do lock profiling ... > > Or if it is, some debloating might be in order - and the detaching of event > enumeration and ftrace TRACE_EVENT infrastructure from other ftrace bits. (i > suggested an '/eventfs' special filesystem before, for nicely layed out > hierarchy of ftrace/perf events.)
Actually, we already have a way to decouple it.
include/trace/define_trace.h is the file that just adds the tracepoint that is needed.
include/trace/ftrace.h is the file that does the magic and adds the code for callbacks and tracing.
The perf hooks probably should not have gone in that file and been put into a include/trace/perf.h file, and then in define_trace.h we would add:
#ifdef CONFIG_EVENT_TRACING #include <trace/ftrace.h> #endif
+#ifdef CONFIG_PERF_EVENTS +#include <trace/perf.h> +#endif
This should be done anyway. But it would also let you decouple ftrace trace events from perf trace events but still let the two use the same trace points.
-- Steve
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