Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
From:   Toke =?utf-8?Q?H=C3=B8iland-J=C3=B8rgensen?= <toke@redhat.com>
To:     Luigi Rizzo <lrizzo@google.com>, netdev@vger.kernel.org,
        davem@davemloft.net, hawk@kernel.org, sameehj@amazon.com
Cc:     linux-kernel@vger.kernel.org, Luigi Rizzo <lrizzo@google.com>
Subject: Re: [PATCH v4] netdev attribute to control xdpgeneric skb linearization
In-Reply-To: <20200228105435.75298-1-lrizzo@google.com>
References: <20200228105435.75298-1-lrizzo@google.com>
Date:   Fri, 28 Feb 2020 12:20:33 +0100
Message-ID: <875zfrufem.fsf@toke.dk>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: quoted-printable
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Luigi Rizzo <lrizzo@google.com> writes:

> Add a netdevice flag to control skb linearization in generic xdp mode.
>
> The attribute can be modified through
> 	/sys/class/net/<DEVICE>/xdpgeneric_linearize
> The default is 1 (on)
>
> Motivation: xdp expects linear skbs with some minimum headroom, and
> generic xdp calls skb_linearize() if needed. The linearization is
> expensive, and may be unnecessary e.g. when the xdp program does
> not need access to the whole payload.
> This sysfs entry allows users to opt out of linearization on a
> per-device basis (linearization is still performed on cloned skbs).
>
> On a kernel instrumented to grab timestamps around the linearization
> code in netif_receive_generic_xdp, and heavy netperf traffic with 1500b
> mtu, I see the following times (nanoseconds/pkt)
>
> The receiver generally sees larger packets so the difference is more
> significant.
>
> ns/pkt                   RECEIVER                 SENDER
>
>                     p50     p90     p99       p50   p90    p99
>
> LINEARIZATION:    600ns  1090ns  4900ns     149ns 249ns  460ns
> NO LINEARIZATION:  40ns    59ns    90ns      40ns  50ns  100ns
>
> v1 --> v2 : added Documentation
> v2 --> v3 : adjusted for skb_cloned
> v3 --> v4 : renamed to xdpgeneric_linearize, documentation
>
> Signed-off-by: Luigi Rizzo <lrizzo@google.com>

Acked-by: Toke H=C3=B8iland-J=C3=B8rgensen <toke@redhat.com>