The pending diff adds pread/pwrite operations to the VFS layer and makes
use of them in the I/O path. The profiling stats are updated
correspondingly.

There is not much performance advanage additional to using spinlocks (a
consistent 2% - 7% increase in throughput), but there is a significant
benefit to using p{read,write} with fcntl tdb locking (5% - 30% increase in
throughput). The largest improvements are in high packet rate workloads (ie,
small blocks sizes and meta-data workloads), as you might expect.

I can provide detailed numbers (packet rate, cpu usage, NIC throughput, etc)
if that would be useful.