Messages in this thread | | | Date | Wed, 3 Dec 2008 14:19:32 +0100 | From | "Frédéric Weisbecker" <> | Subject | Re: [PATCH 4/5] ftrace: function graph return for function entry |
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2008/12/3 Steven Rostedt <rostedt@goodmis.org>: > > On Wed, 3 Dec 2008, Ingo Molnar wrote: > >> >> * Steven Rostedt <rostedt@goodmis.org> wrote: >> >> > From: Steven Rostedt <srostedt@redhat.com> >> > >> > Impact: feature, let entry function decide to trace or not >> > >> > This patch lets the graph tracer entry function decide if the tracing >> > should be done at the end as well. This requires all function graph >> > entry functions return 1 if it should trace, or 0 if the return should >> > not be traced. >> >> > diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S >> > index 47aa5f0..cef05a2 100644 >> > --- a/arch/x86/kernel/entry_64.S >> > +++ b/arch/x86/kernel/entry_64.S >> > @@ -119,6 +119,9 @@ ENTRY(mcount) >> > #ifdef CONFIG_FUNCTION_GRAPH_TRACER >> > cmpq $ftrace_stub, ftrace_graph_return >> > jnz ftrace_graph_caller >> > + >> > + cmpq $ftrace_graph_entry_stub, ftrace_graph_entry >> > + jnz ftrace_graph_caller >> >> hm, that's in the hotpath. What's the point of this? Do we want some sort >> of configuration vector that allows per function graphing versus >> entry-only traces? > > Actually, I'm fine with taking it out. But when we register a function > graph, we register both a entry and exit. I would think it should still > work if one was still set as the default. Unless we document it someplace > that either the entry or exit must be set.
I like it that way too. One should choose wether setting a callback on entry or return or both. But it makes sense for me that should work with only one...
...unless. Actually setting only a callback on entry shoud better been done from the ftrace-function-tracer.
> This change has the function graph work if one or the other is set to > something other than the default. > > Also, this is only in the static ftrace path, not dynamic, but then again, > maybe that means it is even hotter. > > I'm fine with pulling this out. It was not really needed, I was just > trying to make it intuitive. > > -- Steve >
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