lkml.org 
[lkml]   [2006]   [Oct]   [11]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: Dropping NETIF_F_SG since no checksum feature.
    Quoting r. Steven Whitehouse <steve@chygwyn.com>:
    > Subject: Re: Dropping NETIF_F_SG since no checksum feature.
    >
    > 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.

    Will do - thanks for the tips.

    > Also all subject to approval by davem and shemminger of course :-)

    Goes without saying :)

    > 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.

    --
    MST
    -
    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/

    \
     
     \ /
      Last update: 2006-10-11 22:55    [W:0.027 / U:34.044 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site