Re: Accelerated receive flow steering (aRFS) for UDP

On Sun, 2016-10-09 at 19:48 +0000, Chopra, Manish wrote:

Hi Eric, I used "-n" as well with "-N" but still the problem doesn't
go away.

This is what I have done -

Started "netserver" on local/test setup

#netserver
Starting netserver with host 'IN(6)ADDR_ANY' port '12865' and family
AF_UNSPEC

It starts listening on port "12865"

From remote setup, started multiple netperf using different ports for
data sockets specified using "-P" with "-N" and "-n" options specified
as well.
netperf -H 192.168.200.40 -l 150 -t UDP_STREAM -T 8,8 -- -N -n -m 1400
-P 6660,5550 &
netperf -H 192.168.200.40 -l 150 -t UDP_STREAM -T 9,9 -- -N -n -m 1400
-P 9990,9880 &
netperf -H 192.168.200.40 -l 150 -t UDP_STREAM -T 10,10 -- -N -n -m
1400 -P 4455,4400 &
netperf -H 192.168.200.40 -l 150 -t UDP_STREAM -T 11,11 -- -N -n -m
1400 -P 3300,7800 &
netperf -H 192.168.200.40 -l 150 -t UDP_STREAM -T 12,12 -- -N -n -m
1400 -P 50512,44444 &
netperf -H 192.168.200.40 -l 150 -t UDP_STREAM -T 13,13 -- -N -n -m
1400 -P 10512,45672 &
netperf -H 192.168.200.40 -l 150 -t UDP_STREAM -T 14,14 -- -N -n -m
1400 -P 8888,56721 &
netperf -H 192.168.200.40 -l 150 -t UDP_STREAM -T 15,15 -- -N -n -m
1400 -P 9300,8899 &

When on local/test receiving setup, I dump skb's IP header protocol
field in .ndo_rx_flow_steer() handler - it is still always
IPPROTO_TCP.
Which has destined port 12865. But that handler never receives a SKB
whose IP header protocol field is set to IPPROTO_UDP.

As suspected, I believe in receive flow, packets always go in the path
where it never match any entry in global flow table in get_rps_cpu()
function
,possibly due to packets don't get received from the flow of
inet_recvmsg() which updates the global flow table ?

3571                 /* First check into global flow table if there is
a match */
3572                 ident = sock_flow_table->ents[hash &
sock_flow_table->mask];
3573                 if ((ident ^ hash) & ~rps_cpu_mask)
3574                         goto try_rps;

Hence, it never call set_rps_cpu() which internally is supposed to
call .ndo_rx_flow_steer() for the SKB's whose flows to be steered.

On another side, when I use "Iperf" for sending UDP stream, which I
believe receives the packets from the intet_recvmsg() flow
and I do see flows getting steered for UDP packets. [Actually seeing
SKB's whose IP header protocol set to IPPROTO_UDP arriving
in .ndo-rx_flow_steer()].

iperf -s -u
iperf -u -c 192.168.200.40 -t 3000 -i 10 -P 8

OK, I am adding/CC Rick Jones, netperf author, since it seems a netperf
bug, not a kernel one.

I believe I already mentioned fact that "UDP_STREAM -- -N" was not doing
a connect() on the receiver side.