Re: [RFC PATCH] net: add additional lock to qdisc to increase enqueue/dequeue fairness

Rick Jones
2010-03-23T20:40:03Z

Alexander Duyck wrote:
> The qdisc layer shows a significant issue when you start transmitting from
> multiple CPUs. The issue is that the transmit rate drops significantly, and I
> believe it is due to the fact that the spinlock is shared between the 1
> dequeue, and n-1 enqueue cpu threads. In order to improve this situation I am
> adding one additional lock which will need to be obtained during the enqueue
> portion of the path. This essentially allows sch_direct_xmit to jump to
> near the head of the line when attempting to obtain the lock after
> completing a transmit.
>
> Running the script below I saw an increase from 200K packets per second to
> 1.07M packets per second as a result of this patch.
>
> for j in `seq 0 15`; do
> for i in `seq 0 7`; do
> netperf -H <ip> -t UDP_STREAM -l 600 -N -T $i -- -m 6 &
> done
> done

Wow - someone is using the no control connection mode in netperf :) Or were you
actually trying to get the test-specific -N option to control whether or not
netperf "connects" the UDP socket?

rick jones