net: rmnet_data: Add a GRO flush timer

The current GRO implementation relies on NET_RX to complete
processing or the max possible TCP segment size for it to flush the
GRO coalesced packets. This leads to coalescing a large number of
packets which translates to very few ACKs. Since the number of
ACKs are very few and delayed during the slow start phase (stretch
ACK's), we see that the initial throughput ramp up is slow compared
to normal RFC TCP where we send an ACK per two packets. Note that
there is no difference between GRO and non GRO after the max window
size is reached.

Add a mechanism within rmnet_data to force the flush of packets
every 10 micro seconds (experimentally determined) by default. This
is controlled by the module parameter "gro_flush_time" and can be
configured to any value less than a second. To disable this feature,
set this entry to 0.

This reduces the coalesce of packets which translates to increased
number of ACK's compared to normal GRO but lesser ACK's compared
to NO GRO. There is no increase in power for a day to day use case.
Note that this optimization is specific to TCP GRO path only.

Some useful stats below for TCP DL at 400Mbps -

                       |TCP GRO Default | TCP GRO flush timer 10us
==================================================================
iperf 1st second tput  |    300Mbps     |        330Mbps
coalesce ratio         |     15         |         4.5

CRs-Fixed: 961186
Change-Id: Ie8d76c493d61f3f4c256dbaa0378b22a361eed49
Signed-off-by: Subash Abhinov Kasiviswanathan <subashab@codeaurora.org>

0 files changed, 0 insertions, 0 deletions