On Sun, Jun 29, 2003 at 10:37:12AM -0400, Ronghua Zhang wrote:
> Hi,
> I came to a situation that requires to send multiple TCP packets (one
> for each connection) from a kernel thread as soon as possible. The
> following is the skeleton of my code:
I should say this is a heissenbug ... one which happens because
you are observing it with printk().
> kernel_thread()
> {
> foreach sk in (alive connections){
> tp = &(sk->tp_pinfo.af_tcp);
>
> skb = alloc_skb(xxx, GFP_ATOMIC);
> /* build TCP header */
> tcp_build_and_update_options(.....);
> tp->af_specific->send_check(sk, th, skb->len, skb);
>
> tp->af_specific->queue_xmit(skb);
> printk("packet send out for sk %p, at %lu\n", sk, jiffies);
> }
> }
>
> the output is always like this:
> packet send out for sk 1 at 1000
> packet send out for sk 2 at 1001
> packet send out for sk 3 at 1002
> ...
>
> It looks like this kernel thread get rescheduled after it has sent out 1
> packet. But why? each iteration certainly does not need 10ms, why it get
> rescheduled? Is it because af_specific->queue_xmit() is blocking
> operation? but I notice that tcp_transmit_skb() also call it, and
> tcp_transmit_skb() should not call any blockalbe operation. I try to
> increase its priority or change its schedule policy,but has no effect
> at all. Any suggestion is appreciated! This is really urgent.
>
>
> Ronghua
> -
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