Re: 3.7.8/amd64 full interrupt hangs due to iwlwifi under big nfs copies out

Johannes Berg
2013-02-20T17:00:45Z

On Wed, 2013-02-20 at 08:55 -0800, Eric Dumazet wrote:

> > > It will make a huge difference, even on non pressure mode, as TCP
> > > receive window will grow twice faster.
> >
> > Hmm, why does that depend on the allocation size?
>
> I guess you missed all the patches about skb->truesize on netdev

Yeah, I don't follow netdev much any more...

> > > - skb = alloc_skb(128, GFP_ATOMIC);
> > > + fraglen = 128;
> > > + /* if we use order-1 pages, copy to get better TCP performance */
> > > + if (rxb->truesize > PAGE_SIZE)
> > > + fraglen = max_t(unsigned, fraglen, len);
> > > +
> > > + skb = alloc_skb(fraglen, GFP_ATOMIC);
> >
> > Hmm, I don't quite understand -- that's not doing any copy?
> >
> > FWIW if you do the copy you should not "steal" the pages, then they'd be
> > recycled in the RX ring right away.
>
> Code should just works, please read the following lines in the same
> function....
>
> /* If frame is small enough to fit in skb->head, pull it completely.
> * If not, only pull ieee80211_hdr so that splice() or TCP coalesce
> * are more efficient.
> */

Oh, right, though I guess the comment is now wrong since practically
every packet will be copied either here or in mac80211 (A-MSDUs are
split up there)

johannes