osd: conditionally disable dlclose of erasure code plugins

When profiling, tools such as valgrind --tool=callgrind require that the
dynamically loaded libraries are not dlclosed so they can collect usage
information.

The public ErasureCodePluginRegistry::disable_dlclose boolean is introduced
for this purpose.

Signed-off-by: Loic Dachary <loic@dachary.org>
osd: better performances for the erasure code example

The XOR based example is ten times slower than it could because it uses
the buffer::ptr[] operator. Use a temporary char * instead. It performs
as well as jerasure Reed Solomon when decoding with a single erasure:

$ ceph_erasure_code_benchmark \
   --plugin example  --parameter erasure-code-directory=.libs \
   --parameter erasure-code-technique=example \
   --parameter erasure-code-k=2 --parameter erasure-code-m=1 \
   --erasure 1 --workload decode --iterations 5000
8.095007	5GB

$ ceph_erasure_code_benchmark \
   --plugin jerasure  --parameter erasure-code-directory=.libs \
   --parameter erasure-code-technique=reed_sol_van \
   --parameter erasure-code-k=10 --parameter erasure-code-m=6 \
   --erasure 1 --workload decode --iterations 5000
7.870990	5GB

Signed-off-by: Loic Dachary <loic@dachary.org>
osd: set erasure code packet size default to 2048

As shown in
https://www.usenix.org/legacy/events/fast09/tech/full_papers/plank/plank_html/
under "Impact of the Packet Size", the optimal for is in the order of 1k
rather than the current default of 8. Benchmarks are required to find
the actual optimum.

Signed-off-by: Loic Dachary <loic@dachary.org>
osd: erasure code benchmark tool

Implement the ceph_erasure_code_benchmark utility to:

* load an erasure code plugin

* loop over the encode/decode function using the parameters from the
  command line

* print the number of bytes encoded/decoded and the time to process

When decoding, random chunks ( as set with --erasures ) are lost on each
run.

For instance:

    $ ceph_erasure_code_benchmark \
       --plugin jerasure \
       --parameter erasure-code-directory=.libs \
       --parameter erasure-code-technique=reed_sol_van \
       --parameter erasure-code-k=2 \
       --parameter erasure-code-m=2 \
       --workload decode \
       --erasures 2 \
       --iterations 1000
    0.964759	1048576

shows 1GB is decoded in 1second.

It is intended to be used by other scripts to present a human readable
output or detect performance regressions.

Signed-off-by: Loic Dachary <loic@dachary.org>
osd: erasure code benchmark workunit

Display benchmark results for the default erasure code plugins, in a tab
separated CSV file. The first two column contain the amount of KB
that were coded or decoded, for a given combination of parameters
displayed in the following fields.

seconds	KB	plugin	k	m	work.	iter.	size	eras.
1.2	10	example	2	1	encode	10	1024	0
0.5	10	example	2	1	decode	10	1024	1

It can be used as input for a human readable report. It is also intented
to be used to show if a given version of an erasure code plugin performs
better than another.

The last column ( not shown above for brievety ) is the exact command
that was run to produce the result so it can be copy / pasted to
reproduce them or to profile.

Only the jerasure techniques mentionned in
https://www.usenix.org/legacy/events/fast09/tech/full_papers/plank/plank_html/
are benchmarked, the others are assumed to be less interesting.

Signed-off-by: Loic Dachary <loic@dachary.org>
osd: erasure code benchmark is installed is part of ceph-test

Add to the packaging for RPMs and DEBs

Signed-off-by: Loic Dachary <loic@dachary.org>
osd: git ignore erasure code benchmark binary

Signed-off-by: Loic Dachary <loic@dachary.org>
Merge pull request #933 from dachary/wip-erasure-code-benchmark

osd: erasure code benchmark tool

Reviewed-by: Andreas Peters <andreas.joachim.peters@cern.ch>
Reviewed-by: Christophe Courtaut <christophe.courtaut@gmail.com>