common: remove dead code in buffer.cc

Signed-off-by: Loic Dachary <loic-201408@dachary.org>
common: add an aligned buffer with less alignment than a page

SIMD optimized erasure code computation needs aligned memory. Buffers
aligned to a page boundary are not needed though. The buffers used
for the erasure code computation are typical smaller than a page.

The typical alignment requirements SIMD operations are 16 bytes for
SSE2 and NEON and 32 bytes for AVX/AVX2.

Add new prototypes with an align argument, similar to the one enforcing
page alignment. The implementation is exactly the same, except for the
align parameter. The page alignment method are then implemented as calls
to the more generic methods.

The align parameter is an unsigned (same type as CEPH_PAGE_SIZE). The
CEPH_PAGE_MASK value ( ~(CEPH_PAGE_SIZE - 1) ) was only used as
~CEPH_PAGE_MASK, i.e. equivalent of (CEPH_PAGE_SIZE - 1) once the double
~~ is reduced. These occurrence are replaced with (align - 1). The type
of CEPH_PAGE_MASK is an unsigned long which probably because it was
~(CEPH_PAGE_SIZE). When using (align - 1) as a mask for both
CEPH_PAGE_SIZE and SIMD alignment there is no need to use an unsigned
long because there is no risk of overflowing the unsigned value.

The CYGWIN specific code is also modified but not tested.

Unit tests are added for the new methods.

Signed-off-by: Janne Grunau <j@jannau.net>
Signed-off-by: Loic Dachary <loic-201408@dachary.org>
erasure code: use a function for the chunk mapping index
erasure code: use 32-byte aligned buffers

Requiring page aligned buffers and realigning the input if necessary
creates measurable oberhead. ceph_erasure_code_benchmark is between
10-20% faster depending on the workload.

Also prevents a misaligned buffer when bufferlist::c_str(bufferlist)
has to allocate a new buffer to provide continuous one. See bug #9408

Signed-off-by: Janne Grunau <j@jannau.net>
ceph_erasure_code_benchmark: use 32-byte aligned input

The benchmark is supposed to measure the encoding/decoding speed and
not the overhead of buffer realignments.

Signed-off-by: Janne Grunau <j@jannau.net>
erasure-code: expose ErasureCode::SIMD_ALIGN as a const

For test purposes and it will also be useful for plugins that must
ensure the chunk size is a multiple of SIMD_ALIGN.

Signed-off-by: Loic Dachary <loic-201408@dachary.org>
erasure-code: add ErasureCode::encode unit test

Re-create and describe the situation that is fixed by
91a7e18f60bbc9acab3045baaa1b6505474ec4a9 which reworks the buffer
preparation function provided by ErasureCode::encode.

http://tracker.ceph.com/issues/9408 Refs: #9408

Signed-off-by: Loic Dachary <loic-201408@dachary.org>
erasure-code: use ErasureCode::SIMD_ALIGN in ceph_erasure_code_benchmark

Signed-off-by: Loic Dachary <loic-201408@dachary.org>