On Thu, Dec 01, 2016 at 10:34:40AM +0100, Andrey Konovalov wrote: > This patch changes tun.c to call netif_receive_skb instead of netif_rx > when a packet is received (if CONFIG_4KSTACKS is not enabled to avoid > stack exhaustion). The difference between the two is that netif_rx queues > the packet into the backlog, and netif_receive_skb proccesses the packet > in the current context. > > This patch is required for syzkaller [1] to collect coverage from packet > receive paths, when a packet being received through tun (syzkaller collects > coverage per process in the process context). > > As mentioned by Eric this change also speeds up tun/tap. As measured by > Peter it speeds up his closed-loop single-stream tap/OVS benchmark by > about 23%, from 700k packets/second to 867k packets/second. > > A similar patch was introduced back in 2010 [2, 3], but the author found > out that the patch doesn't help with the task he had in mind (for cgroups > to shape network traffic based on the original process) and decided not to > go further with it. The main concern back then was about possible stack > exhaustion with 4K stacks. > > [1] https://github.com/google/syzkaller > > [2] https://www.spinics.net/lists/netdev/thrd440.html#130570 > > [3] https://www.spinics.net/lists/netdev/msg130570.html > > Signed-off-by: Andrey Konovalov <andreyk...@google.com>
Acked-by: Michael S. Tsirkin <m...@redhat.com> > --- > > Changes since v1: > - incorporate Eric's note about speed improvements in commit description > - use netif_receive_skb CONFIG_4KSTACKS is not enabled > > drivers/net/tun.c | 6 ++++++ > 1 file changed, 6 insertions(+) > > diff --git a/drivers/net/tun.c b/drivers/net/tun.c > index 8093e39..d310b13 100644 > --- a/drivers/net/tun.c > +++ b/drivers/net/tun.c > @@ -1304,7 +1304,13 @@ static ssize_t tun_get_user(struct tun_struct *tun, > struct tun_file *tfile, > skb_probe_transport_header(skb, 0); > > rxhash = skb_get_hash(skb); > +#ifndef CONFIG_4KSTACKS > + local_bh_disable(); > + netif_receive_skb(skb); > + local_bh_enable(); > +#else > netif_rx_ni(skb); > +#endif > > stats = get_cpu_ptr(tun->pcpu_stats); > u64_stats_update_begin(&stats->syncp); > -- > 2.8.0.rc3.226.g39d4020
