Profiling AES256-OCB encryption and decryption shows that large portion of gnupg program time is spent in memcpy functions. Most of these memory copies are done from iobuf read/write functions and estream es_write_fbf function as can be seen in these "flamegraphs":

For CFB/MDC, memory copies have lesser effect as encryption and decryption are slower because of additional SHA1 processing:

Following patches try to minimize these memory copies in iobuf, estream and cipher-aead.c. For estreams, buffering is disabled as input is already provided as large buffers. cipher-aead.c:do_hash is changed to avoid additional memory copy when possible. For iobuf_read and iobuf_write new zerocopy mode of operation is added, that is avoiding coping to internal drain buffer when output/input buffer is large.

Which these patches, memory copy overhead is mostly eliminated as can be seen from these flamegraphs:

Benchmark results on AMD Ryzen 5800X:

                         Before           After
AES256-OCB encryption     1960 MiB/s       5300 MiB/s
AES256-OCB decryption     4040 MiB/s       5350 MiB/s
AES256-CFB encryption      750 MiB/s        760 MiB/s
AES256-CFB decryption     1590 MiB/s       1610 MiB/s