erasure-code: cauchy techniques allow w 8,16,32

Enforce the restriction at initialization time, the same way it is done
for Reed Solomon. Choosing a w value different from 8,16,32 will lead to
memory corruption that cannot easily be traced to the cause.

Signed-off-by: Loic Dachary <loic@dachary.org>
erasure-code: implement alignment on chunk sizes

jerasure expects chunk sizes that are aligned on the largest possible
vector size that could be used by SSE instructions, when available (
LARGEST_VECTOR_WORDSIZE == 16 bytes ).

For techniques derived from Cauchy, encoding and decoding is done by
subdividing the chunk into packets of packetsize bytes. The operations
are done w * packetsize bytes at a time. It follows that each chunk must
have a size that is a multiple of w * packetsize bytes.

For techniques derived from Vandermonde, it is enough for a chunk to be
a multiple of w * LARGEST_VECTOR_WORDSIZE.

ErasureCodeJerasure::get_alignment returns a size alignment constraint
that has to be enforced as a multiple of the object size. The resulting
object size then has to match the chunk constraints described above
although they have no relationship with K. For Cauchy, it leads to
excessive padding, making it impossible to set sensible parameters for
when the object size is small.

When the per_chunk_alignement data member is true, the semantic of
ErasureCodeJerasure::get_alignment is changed to return a size alignment
constraint to be enforced as a multiple of the chunk size. The
ErasureCodeJerasure::get_chunk_size method is modified to use the new
semantic when appropriate.

The jerasure-per-chunk-alignement parameter is parsed to set
per_chunk_alignement for the Vandermonde and Cauchy techniques.

The memory address of a chunk is implicitly aligned to a page boundary
because it is allocated with buffer::create_page_aligned.

http://tracker.ceph.com/issues/8475 Fixes: #8475

Signed-off-by: Loic Dachary <loic@dachary.org>
erasure-code: reduce jerasure verbosity

Only output a message about adjusting the buffer size when it is
adjusted, not when the size does not need adjustment.

Signed-off-by: Loic Dachary <loic@dachary.org>
erasure-code: control jerasure plugin variant selection

The jerasure-variant parameter is interpreted as the name of the plugin
variant to be loaded regardless of the available CPU features. The
values can be sse3, sse4, generic. It is undocumented and meant for
benchmarking purposes, primarily to force the generic plugin to be
loaded when the sse4 would be chosen.

Signed-off-by: Loic Dachary <loic@dachary.org>
erasure-code: properly indent ErasureCodePluginSelectJerasure.cc

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

Expand the default suite to enumerate all cases that are relevant to the
current code base so that it is easier to consume. Namely it means

 * iterating over object sizes of 4KB (what is used by default) and
   1MB (what was previous benchmarked)
 * grouping results in series that would make sense to plot to get the
   behavior of a given technique for a series of K/M values and all
   possible erasures.

Instead of specifying the iterations to run, set the size of the total
data set to be exercised and compute the iterations by dividing it by
the object size. Since the object size varies, it is impractical to
preset the number of iterations and get meaningful results.

The PARAMETERS environment variable is added to enable the caller to
inject --parameter jerasure-variant=generic, for instance.

The packets size is calculated based on the other parameters. The
options are limited when packets are small (4KB) and it would not make a
real difference to give control over it. The packet size is capped to
a maximum of 3100 bytes which is roughly what has been found to be an
optimal value for large packets (1MB).

Signed-off-by: Loic Dachary <loic@dachary.org>
COPYING: Cloudwatt copyright is inline

Remove partial list of contributions since Cloudwatt copyright has been
placed in the copyright notices of the files where works covered by
copyright have been included.

Signed-off-by: Loic Dachary <loic@dachary.org>
erasure-code: HTML display of benchmark results

The ceph_erasure_code_benchmark output is converted into a JSON series
suitable to display in HTML with the http://www.flotcharts.org/
library. A self contained copy of the HTML,JS,CSS files is included for
durability and can be used from the source tree with:

    CEPH_ERASURE_CODE_BENCHMARK=src/ceph_erasure_code_benchmark  \
    PLUGIN_DIRECTORY=src/.libs \
        qa/workunits/erasure-code/bench.sh fplot jerasure |
        tee qa/workunits/erasure-code/bench.js

and display with:

    firefox qa/workunits/erasure-code/bench.html

Signed-off-by: Loic Dachary <loic@dachary.org>
Merge pull request #1875 from dachary/wip-8437

erasure-code: benchmarking jerasure

Reviewed-by: Sage Weil <sage@redhat.com>