Re: [PATCH RFC 0/3] Static calls

[Steven Rostedt]

On Fri, 9 Nov 2018 10:41:37 -0600
Josh Poimboeuf <jpoimboe@xxxxxxxxxx> wrote:

> On Fri, Nov 09, 2018 at 09:21:39AM -0600, Josh Poimboeuf wrote:
> > On Fri, Nov 09, 2018 at 07:16:17AM -0800, Andy Lutomirski wrote:  
> > > On Thu, Nov 8, 2018 at 11:28 PM Ingo Molnar <mingo@xxxxxxxxxx> wrote:  
> > > >
> > > >
> > > > All other usecases are bonus, but it would certainly be interesting to
> > > > investigate the impact of using these APIs for tracing: that too is a
> > > > feature enabled everywhere but utilized only by a small fraction of Linux
> > > > users - so literally every single cycle or instruction saved or hot-path
> > > > shortened is a major win.  
> > > 
> > > For tracing, we'd want static_call_set_to_nop() or something like that, right?  
> > 
> > Are we talking about tracepoints?  Or ftrace?  
> 
> Since ftrace changes calls to nops, and vice versa, I assume you meant
> ftrace.  I don't think ftrace is a good candidate for this, as it's
> inherently more flexible than this API would reasonably allow.
> 

Not sure what Andy was talking about, but I'm currently implementing
tracepoints to use this, as tracepoints use indirect calls, and are a
prime candidate for static calls, as I showed in my original RFC of
this feature.

-- Steve