unlikely compiler flag propagation

[Nicholas Mc Guire]

On Wed, 18 Feb 2015, Valdis.Kletnieks at vt.edu wrote:

> On Wed, 18 Feb 2015 19:38:01 +0100, Nicholas Mc Guire said:
> > On Wed, 18 Feb 2015, Greg KH wrote:
> 
> > interesting - would you have a reference to some talk/paper/data/... ?
> 
> Test for yourself :)
> 
> config PROFILE_ANNOTATED_BRANCHES
>         bool "Trace likely/unlikely profiler"
>         select TRACE_BRANCH_PROFILING
>         help
>           This tracer profiles all likely and unlikely macros
>           in the kernel. It will display the results in:
> 
>           /sys/kernel/debug/tracing/trace_stat/branch_annotated
> 
>           Note: this will add a significant overhead; only turn this
>           on if you need to profile the system's use of these macros.
> 
was not aware of that - many thanks !

I do assume that such a claim of 90% not being effective would
not be based on testing some single system but based on a much 
wider basis so that data would be interesting to see data from
different clases of systems.

thx!
hofrat