Ceph » rbd

Take a trivial program:

$ cat test.c 
  #include <stdlib.h>
  int main () { exit (0); }

and compare the startup time with and without linking to -lrados -lrbd.

Without:

$ gcc test.c -o test
  $ TIMEFORMAT='%R' ; time ./test
  0.001

With:

$ gcc test.c -o test -lrbd
  $ TIMEFORMAT='%R' ; time ./test
  0.044

This really matters - currently initializing librbd consumes
15% of the total time taken to start up the libguestfs appliance.

I looked at the code and did some profiling with perf [see attachment]
and it seems as if the following code is responsible:

https://github.com/ceph/ceph/blob/master/src/common/Cycles.cc#L50

This code is really wrong, but it in lieu of being able to fix it,
it would be nice at least to have an environment variable we can
use to skip the madness.