static user probe performance

[Jim Keniston]

On Wed, 2010-04-07 at 10:43 -0400, Frank Ch. Eigler wrote:
> >> run with stap
> >> [...]
> >> elapsed time
> >>       volatile semaphore 1858.71
> >>       no volatile no semaphore 1865.68
> >>       volatile no semaphore 1873.07
> >>       no volatile semaphore 1878.09
> >
> > So for this particular microbenchmark, systemtap probing imposes a 30x
> > slowdown, yikes.  How many probe hits does this represent?
> 
> From scox's later numbers, that's 192 million hits, for about 9
> us/hit, which seems rather high.

Yes, it is high.  Are you probing a multithreaded app?  We have a known
performance problem there:
http://sourceware.org/bugzilla/show_bug.cgi?id=5660

Jim