Re: [PATCH RFC 0/3] Static calls

[Steven Rostedt]

On Fri, 9 Nov 2018 13:44:09 -0600
Josh Poimboeuf <jpoimboe@xxxxxxxxxx> wrote:

> On Fri, Nov 09, 2018 at 02:37:03PM -0500, Steven Rostedt wrote:
> > On Fri, 9 Nov 2018 11:05:51 -0800
> > Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote:
> >   
> > > > 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.
> > > > 
> > > >     
> > > 
> > > Indeed.
> > > 
> > > Although I had assumed that tracepoints already had appropriate jump label magic.  
> > 
> > It does. But that's not the problem I was trying to solve. It's that
> > tracing took a 8% noise dive with retpolines when enabled (hackbench
> > slowed down by 8% with all the trace events enabled compared to all
> > trace events enabled without retpoline). That is, normal users (those
> > not tracinng) are not affected by trace events slowing down by
> > retpoline. Those that care about performance when they are tracing, are
> > affected by retpoline, quite drastically.
> > 
> > I'm doing another test run and measurements, to see how the unoptimized
> > trampolines help, followed by the trampoline case.  
> 
> Are you sure you're using unoptimized?  Optimized is the default on
> x86-64 (with my third patch).
> 

Yes, because I haven't applied that third patch yet ;-)

Then I'll apply it and see how much that improves things.

-- Steve