From: Andrey Konovalov <andreyk...@google.com>
Date: Thu, 1 Dec 2016 10:34:40 +0100
> 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  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.
>  https://github.com/google/syzkaller
>  https://www.spinics.net/lists/netdev/thrd440.html#130570
>  https://www.spinics.net/lists/netdev/msg130570.html
> Signed-off-by: Andrey Konovalov <andreyk...@google.com>
> Changes since v1:
> - incorporate Eric's note about speed improvements in commit description
> - use netif_receive_skb CONFIG_4KSTACKS is not enabled
Applied to net-next, thanks!