lguest: try to batch interrupts on network receive
authorRusty Russell <rusty@rustcorp.com.au>
Sat, 13 Jun 2009 04:27:12 +0000 (22:27 -0600)
committerRusty Russell <rusty@rustcorp.com.au>
Fri, 12 Jun 2009 12:57:12 +0000 (21:57 +0930)
commit4a8962e21bc505c714fc2508494d4c7dd3fe2d29
tree55afdb7bc1f7e03bc910e59a17962e671a031ebc
parent95c517c09bad31a03e22f2fdb5f0aa26a490a92d
lguest: try to batch interrupts on network receive

Rather than triggering an interrupt every time, we only trigger an
interrupt when there are no more incoming packets (or the recv queue
is full).

However, the overhead of doing the select to figure this out is
measurable: 1M pings goes from 98 to 104 seconds, and 1G Guest->Host
TCP goes from 3.69 to 3.94 seconds.  It's close to the noise though.

I tested various timeouts, including reducing it as the number of
pending packets increased, timing a 1 gigabyte TCP send from Guest ->
Host and Host -> Guest (GSO disabled, to increase packet rate).

// time tcpblast -o -s 65536 -c 16k 192.168.2.1:9999 > /dev/null

Timeout Guest->Host Pkts/irq Host->Guest Pkts/irq
Before 11.3s 1.0 6.3s 1.0
0 11.7s 1.0 6.6s 23.5
1 17.1s 8.8 8.6s 26.0
1/pending 13.4s 1.9 6.6s 23.8
2/pending 13.6s 2.8 6.6s 24.1
5/pending 14.1s 5.0 6.6s 24.4

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Documentation/lguest/lguest.c