On 2014/1/28 22:49, Eric Dumazet wrote:
On Tue, 2014-01-28 at 16:14 +0800, Qin Chuanyu wrote:
according perf test result，I found that there are 5%-8% cpu cost on
softirq by use netif_rx_ni called in tun_get_user.
so I changed the function which cause skb transmitted more quickly.
from
tun_get_user ->
netif_rx_ni(skb);
to
tun_get_user ->
rcu_read_lock_bh();
netif_receive_skb(skb);
rcu_read_unlock_bh();
No idea why you use rcu here ?
The test result is as below:
CPU: Intel(R) Xeon(R) CPU E5620 @ 2.40GHz
NIC: intel 82599
Host OS/Guest OS:suse11sp3
Qemu-1.6
netperf udp 512(VM tx)
test model: VM->host->host
modified before : 2.00Gbps 461146pps
modified after : 2.16Gbps 498782pps
8% performance gained from this change,
Is there any problem for this patch ?
http://patchwork.ozlabs.org/patch/52963/
the problem list above show that:
Since the cgroup classifier has this check:
if (softirq_count() != SOFTIRQ_OFFSET))
return -1;
We still fail to classify the frame.
but the source in the recently version has changed as below:
if (in_serving_softirq()) {
/* If there is an sk_classid we'll use that. */
if (!skb->sk)
return -1;
classid = skb->sk->sk_classid;
}
skb is allocated by tun_alloc_skb, so skb->sk is not NULL.
I think the problem is not existed anymore.
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