netdev - Re: [PATCH net-next] ipv4: use l4 hash for locally generated multipath flows

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Date:	Thu, 29 Oct 2015 22:12:21 +0100
From:	Paolo Abeni <pabeni@...hat.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Peter Nørlund <pch@...bogen.com>,
	netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
	Alexey Kuznetsov <kuznet@....inr.ac.ru>,
	James Morris <jmorris@...ei.org>,
	Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
	Patrick McHardy <kaber@...sh.net>
Subject: Re: [PATCH net-next] ipv4: use l4 hash for locally generated
 multipath flows

On Thu, 2015-10-29 at 11:43 -0700, Eric Dumazet wrote:
> On Thu, 2015-10-29 at 17:52 +0100, Paolo Abeni wrote:
> > On Thu, 2015-10-29 at 08:28 -0700, Eric Dumazet wrote:
> > > On Thu, 2015-10-29 at 16:00 +0100, Paolo Abeni wrote:
> > > 
> > > > This patch do not add dissection code: it use the information provided
> > > > by the available flowi4 structure. Moreover the skb is not available on
> > > > the calling site (in __ip_route_output_key_hash) and pushing it all the
> > > > way will require a lot of intrusive changes. Do you think it's the
> > > > better option ?
> > > 
> > > If skb is provided, then we could use its information.
> > 
> > I see your point, but providing an skb to __ip_route_output_key_hash()
> > is not very viable: it has a lot of indirect callers which are
> > problematic, i.e.:
> > 
> > __ip_route_output_key()
> > ip_route_output_flow()
> > inet_csk_route_req()
> > tcp_v4_send_synack()  <- skb available here, but created using dst
> > information.
> > 
> 
> I never said it was trivial.
> 
> I said : "If skb is provided, then we can use its l4hash"
> 
> If not, then sure, a flow-based hash fallback is better than nothing.

Thank you for all the feedback. I'll resubmit using the flow-based hash.

Paolo

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