Re: [PATCH v2] net:Add sysctl_tcp_sg_max_skb_frags

[Hannes Frederic Sowa]

On 27.01.2016 16:15, Eric Dumazet wrote:
> On Wed, 2016-01-27 at 14:20 +0100, Hans Westgaard Ry wrote:
> > Devices may have limits on the number of fragments in an skb they support.
> > Current codebase uses a constant as maximum for number of fragments one
> > skb can hold and use.
> > When enabling scatter/gather and running traffic with many small messages
> > the codebase uses the maximum number of fragments and may thereby violate
> > the max for certain devices.
> > The patch introduces a global variable as max number of fragments in
> > scatter/gather.
>
>
> Principle looks good, but we have to ask if other skb providers [1] will
> add other sysctl, or if we could share a common one ?
>
> If it is a common one, it should be /proc/sys/net/core/... instead
> of /proc/sys/net/ipv4/tcp_....
>
> Other providers include :
>
> 1) GRO stack
> 2) callers of sock_alloc_send_pskb(), alloc_skb_with_frags(),
> sock_alloc_send_skb() ..

I agree, this knob should get a generic name and live in a generic net/ 
directory to control this globally, so things don't break during 
forwarding etc.

It does not solve the problem completely, e.g. when VMs send gso packets 
through a vhost-net onto IPoIB, no?

Thanks,
Hannes