netdev - Re: [PATCH net-next v3 1/2] ipv6: introduce and uses route look hints for list input

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Message-ID: <5bb4b0b2-cc12-2cce-0122-54bd72ab04e7@gmail.com>
Date:   Tue, 19 Nov 2019 08:39:00 -0700
From:   David Ahern <dsahern@...il.com>
To:     Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org
Cc:     "David S. Miller" <davem@...emloft.net>,
        Willem de Bruijn <willemdebruijn.kernel@...il.com>,
        Edward Cree <ecree@...arflare.com>
Subject: Re: [PATCH net-next v3 1/2] ipv6: introduce and uses route look hints
 for list input

On 11/19/19 7:38 AM, Paolo Abeni wrote:
> When doing RX batch packet processing, we currently always repeat
> the route lookup for each ingress packet. If policy routing is
> configured, and IPV6_SUBTREES is disabled at build time, we
> know that packets with the same destination address will use
> the same dst.
> 
> This change tries to avoid per packet route lookup caching
> the destination address of the latest successful lookup, and
> reusing it for the next packet when the above conditions are
> in place. Ingress traffic for most servers should fit.
> 
> The measured performance delta under UDP flood vs a recvmmsg
> receiver is as follow:
> 
> vanilla		patched		delta
> Kpps		Kpps		%
> 1431		1674		+17

That's a nice boost...

> +static struct sk_buff *ip6_extract_route_hint(struct net *net,
> +					      struct sk_buff *skb)
> +{
> +	if (IS_ENABLED(IPV6_SUBTREES) || fib6_has_custom_rules(net))

... but basing on SUBTREES being disabled is going to limit its use. If
no routes are source based (fib6_src is not set), you should be able to
re-use the hint with SUBTREES enabled. e.g., track fib6_src use with a
per-namespace counter - similar to fib6_rules_require_fldissect.