linux-kernel - Re: [PATCH v2] tun: Use netif_receive_skb instead of netif

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Date:   Wed, 7 Dec 2016 11:21:11 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     David Miller <davem@...emloft.net>, andreyknvl@...gle.com
Cc:     herbert@...dor.apana.org.au, 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



On 2016年12月02日 03:43, David Miller wrote:
> 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!

David, looks like this commit is not in net-next.git.

Please help to check.

Thanks