Re: [PATCH 1/1] TX throttling bug-fixing patch of AX88179_178A

Eric Dumazet
2013-07-22T18:47:21Z

On Mon, 2013-07-22 at 19:38 +0100, Ben Hutchings wrote:
> On Mon, 2013-07-22 at 11:29 -0700, Grant Grundler wrote:
> > On Mon, Jul 22, 2013 at 10:07 AM, Eric Dumazet <eric.dumazet@gmail.com> wrote:
> > ...
> > > I guess that if a driver does not advertise NETIF_F_SG, this
> > > skb_linearize() call is not needed : All frames reaching your xmit
> > > function should already be linear
> >
> > As Ben Hutchings pointed out, hw_features is still setting this...but
> > I'm not sure how that matters.
> >
> > ax88179_set_features() doesn't allow setting SG or TSO features. But
> > I expect it would be "not too difficult" to add such that ethtool
> > could set those features after boot.
> [...]
>
> It already can. That's what putting feature flags in hw_features does.

My original concern, that inspired this patch, was to remove SG support,
as this driver does not have SG support at all.

Linearize a full TSO packet needs order-5 allocations, thats likely to
fail and lead to very slow TCP performance, because it will only rely on
retransmits.