[PATCH net-next 16/37] rxrpc: Implement progressive transmission queue struct

[Jakub Kicinski]

On Mon,  2 Dec 2024 14:30:34 +0000 David Howells wrote:
> We need to scan the buffers in the transmission queue occasionally when
> processing ACKs, but the transmission queue is currently a linked list of
> transmission buffers which, when we eventually expand the Tx window to 8192
> packets will be very slow to walk.
> 
> Instead, pull the fields we need to examine a lot (last sent time,
> retransmitted flag) into a new struct rxrpc_txqueue and make each one hold
> an array of 32 or 64 packets.
> 
> The transmission queue is then a list of these structs, each pointing to a
> contiguous set of packets.  Scanning is then a lot faster as the flags and
> timestamps are concentrated in the CPU dcache.
> 
> The transmission timestamps are stored as a number of microseconds from a
> base ktime to reduce memory requirements.  This should be fine provided we
> manage to transmit an entire buffer within an hour.
> 
> This will make implementing RACK-TLP [RFC8985] easier as it will be less
> costly to scan the transmission buffers.

also possibly transient but clang says:

net/rxrpc/output.c:815:20: warning: unused function 'rxrpc_instant_resend' [-Wunused-function]
  815 | static inline void rxrpc_instant_resend(struct rxrpc_call *call)
      |                    ^~~~~~~~~~~~~~~~~~~~