tree af0fb549b90c85a50b2d3ab17683ce463dbb596d
parent 878ce4cd1d378887b551f604263845f1d4f9d225
author Jungho Ahn <jhahn@google.com> 1432228031 -0700
committer Jungho Ahn <jhahn@google.com> 1432228034 -0700

iobuf: change the way to handle reserve bytes

  Currently, iobuf allocator reserves the space only when it allocates
  the first slice from the internal buf. Also we do not set the 'reserve'
  correctly. E.g., zero reserve in crypto where it is necessary), and
  header+macsize in vc.newWriter where it isn't.
  This leads unnecessary data copy for header+mac insertion and may prevent
  coalescing due to the reserved space.

  This CL change iobuf allocator to always reserve the space when
  requested, and give the correct 'reserve' bytes to each alloc.

                                      old                        new
  RPC Connection                      13.72 ms/rpc               13.70 ms/rpc              -0.1%
  RPC (echo 1000B)                    1.03 ms/rpc (971.45 qps)   1.02 ms/rpc (979.03 qps)  -1.0% (0.8%)
  RPC Streaming (echo 1000B)          0.11 ms/rpc                0.11 ms/rpc                0.0%
  RPC Streaming Throughput (echo 1MB) 293.60 MB/s                328.45 MB/s               11.9%

Change-Id: I081579544540771cf2dfe7aaa433f1a2c5d0f8f2