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

Michael S. Tsirkin
2014-02-11T15:47:02Z

On Tue, Feb 11, 2014 at 07:24:04AM -0800, Eric Dumazet wrote:
> 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 ?
>

But not before making sure (testing) that patch does not break the
cgroups classifier please.

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MST