Messages in this thread | | | Date | Wed, 11 Oct 2006 13:57:20 -0700 | From | Stephen Hemminger <> | Subject | Re: Dropping NETIF_F_SG since no checksum feature. |
| |
On Wed, 11 Oct 2006 21:11:38 +0100 Steven Whitehouse <steve@chygwyn.com> wrote:
> Hi, > > On Wed, Oct 11, 2006 at 05:01:03PM +0200, Michael S. Tsirkin wrote: > > Quoting Steven Whitehouse <steve@chygwyn.com>: > > > > ssize_t tcp_sendpage(struct socket *sock, struct page *page, int offset, > > > > size_t size, int flags) > > > > { > > > > ssize_t res; > > > > struct sock *sk = sock->sk; > > > > > > > > if (!(sk->sk_route_caps & NETIF_F_SG) || > > > > !(sk->sk_route_caps & NETIF_F_ALL_CSUM)) > > > > return sock_no_sendpage(sock, page, offset, size, flags); > > > > > > > > > > > > So, it seems that if I set NETIF_F_SG but clear NETIF_F_ALL_CSUM, > > > > data will be copied over rather than sent directly. > > > > So why does dev.c have to force set NETIF_F_SG to off then? > > > > > > > I agree with that analysis, > > > > So, would you Ack something like the following then? > > > > In so far as I'm able to ack it, then yes, but with the following > caveats: that you also need to look at the tcp code's checks for > NETIF_F_SG (aside from the interface to tcp_sendpage which I think > we've agreed is ok) and ensure that this patch will not change their > behaviour, and here I'm thinking of the test in net/ipv4/tcp.c:select_size() > in particular - there may be others but thats the only one I can think > of off the top of my head. I think this is what davem was getting at > with his comment about copy & sum for smaller packets. > > Also all subject to approval by davem and shemminger of course :-) > > My general feeling is that devices should advertise the features that > they actually have and that the protocols should make the decision > as to which ones to use or not depending on the combinations available > (which I think is pretty much your argument). > > Steve. >
You might want to try ignoring the check in dev.c and testing to see if there is a performance gain. It wouldn't be hard to test a modified version and validate the performance change.
You could even do what I suggested and use skb_checksum_help() to do inplace checksumming, as a performance test.
-- Stephen Hemminger <shemminger@osdl.org> - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |