netdev - Re: [RFC PATCH] reuseport: compute the ehash only if needed

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Date:   Tue, 12 Dec 2017 12:44:01 -0500
From:   Craig Gallek <kraigatgoog@...il.com>
To:     Paolo Abeni <pabeni@...hat.com>
Cc:     netdev <netdev@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>
Subject: Re: [RFC PATCH] reuseport: compute the ehash only if needed

On Tue, Dec 12, 2017 at 8:09 AM, Paolo Abeni <pabeni@...hat.com> wrote:
> When a reuseport socket group is using a BPF filter to distribute
> the packets among the sockets, we don't need to compute any hash
> value, but the current reuseport_select_sock() requires the
> caller to compute such hash in advance.
>
> This patch reworks reuseport_select_sock() to compute the hash value
> only if needed - missing or failing BPF filter. Since different
> hash functions have different argument types - ipv4 addresses vs ipv6
> ones - to avoid over-complicate the interface, reuseport_select_sock()
> is now a macro.
Purely subjective, but I think a slightly more complicated function
signature for reuseport_select_sock (and reuseport_select_sock6?)
would look a little better than this macro.  It would avoid needing to
expose the reuseport_info struct and would keep the rcu semantics
entirely within the function call (the fast-path memory access
semantics here are already non-trivial...)

> Additionally, the sk_reuseport test is move inside reuseport_select_sock,
> to avoid some code duplication.
>
> Overall this gives small but measurable performance improvement
> under UDP flood while using SO_REUSEPORT + BPF.
Exciting, do you have some specific numbers here?  I'd be interested
in knowing what kinds of loads you end up seeing improvements for.

> Signed-off-by: Paolo Abeni <pabeni@...hat.com>