Re: [PATCH v2] net-tcp: TCP/IP stack bypass for loopback connections

On 08/10/2012 01:52 AM, Bruce "Brutus" Curtis wrote:

From: "Bruce \"Brutus\" Curtis" <redacted>

TCP/IP loopback socket pair stack bypass, based on an idea by, and
rough upstream patch from, David Miller [off-list ref] called
"friends", the data structure modifcations and connection scheme are
reused with extensive data-path changes.

A new sysctl, net.ipv4.tcp_friends, is added:
  0: disable friends and use the stock data path.
  1: enable friends and bypass the stack data path, the default.

Note, when friends is enabled any loopback interpose, e.g. tcpdump,
will only see the TCP/IP packets during connection establishment and
finish, all data bypasses the stack and instead is delivered to the
destination socket directly.

Testing done on a 4 socket 2.2GHz "Quad-Core AMD Opteron(tm) Processor
8354 CPU" based system, netperf results for a single connection show
increased TCP_STREAM throughput, increased TCP_RR and TCP_CRR transaction
rate for most message sizes vs baseline and comparable to AF_UNIX.

Significant increase (up to 4.88x) in aggregate throughput for multiple
netperf runs (STREAM 32KB I/O x N) is seen.

Nice!

Just to quantify the loopback testing compat issue.
I often do stuff like the following to test latency.
Will that be impacted?

  tc qdisc add dev lo root handle 1:0 netem delay 20msec

As for the stated tcpdump change,
I don't suppose it would be possible to dynamically
disable this (for new connections at least)
while lo is being dumped?

cheers,
Pádraig.