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Date: Thu, 01 Dec 2016 14:43:57 -0500 (EST) From: David Miller <davem@...emloft.net> To: andreyknvl@...gle.com Cc: herbert@...dor.apana.org.au, jasowang@...hat.com, edumazet@...gle.com, pmk@...gle.com, pabeni@...hat.com, mst@...hat.com, soheil@...gle.com, elfring@...rs.sourceforge.net, rppt@...ux.vnet.ibm.com, netdev@...r.kernel.org, linux-kernel@...r.kernel.org, dvyukov@...gle.com, kcc@...gle.com, syzkaller@...glegroups.com Subject: Re: [PATCH v2] tun: Use netif_receive_skb instead of netif_rx From: Andrey Konovalov <andreyknvl@...gle.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 [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 <andreyknvl@...gle.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!
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