netdev - Re: [PATCH] tun: use netif_receive_skb instead of netif_rx

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Message-ID: <1392132244.6615.83.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Tue, 11 Feb 2014 07:24:04 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Qin Chuanyu <qinchuanyu@...wei.com>
Cc:	davem@...emloft.net, jasowang@...hat.com,
	"Michael S. Tsirkin" <mst@...hat.com>,
	Anthony Liguori <anthony@...emonkey.ws>,
	KVM list <kvm@...r.kernel.org>, netdev@...r.kernel.org
Subject: Re: [PATCH] tun: use netif_receive_skb instead of netif_rx_ni

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@...wei.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 ?



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