Re: [PATCH RFC 0/3] Static calls

[Andy Lutomirski]

> On Nov 9, 2018, at 10:42 AM, Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
> 
> 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.
> 
> 

Indeed.

Although I had assumed that tracepoints already had appropriate jump label magic.