On Wed, 2015-08-19 at 19:17 +0000, Grumbach, Emmanuel wrote:
> Hm.. how would net/core/tso.c avoid this?
Because a driver using these helpers keep around the original LSO packet
and frees it normally at TX completion time.
> I can't see anything related to truesize there.
> Note that this work since it is guaranteed that we release the skbs in
> order.
>
> >
> > (BTW TCP packets do not have sock_wfree as destructor but tcp_wfree(),
> > yet we want backpressure mostly for TCP stack (TCP Small Queues))
> >
> >
>
> I am not sure I follow here.
> You want me to test:
> if (skb_gso->destructor == tcp_wfree) ?
Yes.
Look for example at tcp_gso_segment() (called from skb_gso_segment())
copy_destructor = gso_skb->destructor == tcp_wfree;
...
/* Following permits TCP Small Queues to work well with GSO :
* The callback to TCP stack will be called at the time last frag
* is freed at TX completion, and not right now when gso_skb
* is freed by GSO engine
*/
if (copy_destructor) {
swap(gso_skb->sk, skb->sk);
swap(gso_skb->destructor, skb->destructor);
sum_truesize += skb->truesize;
atomic_add(sum_truesize - gso_skb->truesize,
&skb->sk->sk_wmem_alloc);
}
>
> I checked that code using iperf and saw that I don't get into this if,
> but I (probably wrongly) assumed that other applications would set a
> flag on the socket (forgive my ignorance) that would make this if be taken.
If you do not see skb->destructor == tcp_wfree, then something is
definitely wrong on your setup.
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