Re: [PATCH] tun: use netif_receive_skb instead of netif_rx_ni

Eric Dumazet
2014-02-11T15:24:07Z

On Tue, 2014-02-11 at 22:25 +0800, Qin Chuanyu wrote:
> we could xmit directly instead of going through softirq to gain
> throughput and lantency improved.
> test model: VM-Host-Host just do transmit. with vhost thread and nic
> interrupt bind cpu1. netperf do throuhput test and qperf do lantency test.
> Host OS: suse11sp3, Guest OS: suse11sp3
>
> latency result(us):
> packet_len 64 256 512 1460
> old(UDP) 44 47 48 66
> new(UDP) 38 41 42 66
>
> old(TCP) 52 55 70 117
> new(TCP) 45 48 61 114
>
> throughput result(Gbit/s):
> packet_len 64 512 1024 1460
> old(UDP) 0.42 2.02 3.75 4.68
> new(UDP) 0.45 2.14 3.77 5.06
>
> TCP due to the latency, client couldn't send packet big enough
> to get benefit from TSO of nic, so the result show it will send
> more packet per sencond but get lower throughput.
>
> Eric mentioned that it would has problem with cgroup, but the patch
> had been sent by Herbert Xu.
> patch_id f845172531fb7410c7fb7780b1a6e51ee6df7d52
>
> Signed-off-by: Chuanyu Qin <qinchuanyu@huawei.com>
> ---
> drivers/net/tun.c | 4 +++-
> 1 files changed, 3 insertions(+), 1 deletions(-)
>
> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> index 44c4db8..90b4e58 100644
> --- a/drivers/net/tun.c
> +++ b/drivers/net/tun.c
> @@ -1184,7 +1184,9 @@ 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);
> - netif_rx_ni(skb);
> + rcu_read_lock_bh();
> + netif_receive_skb(skb);
> + rcu_read_unlock_bh();
>
> tun->dev->stats.rx_packets++;
> tun->dev->stats.rx_bytes += len;

I already said this patch is not good :

rcu_read_lock_bh() makes no sense here.

What is really needed is local_bh_disable();

Herbert patch ( http://patchwork.ozlabs.org/patch/52963/ ) had a much
cleaner form.

Just use it, CC him, credit him, please ?