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Tsirkin" To: Jiri Pirko Subject: Re: [patch net-next] net: virtio_net: implement exact header length guest feature Message-ID: <20230217083915-mutt-send-email-mst@kernel.org> References: <20230217121547.3958716-1-jiri@resnulli.us> <20230217072032-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Disposition: inline Cc: Vitaly Mireyno , netdev@vger.kernel.org, virtualization@lists.linux-foundation.org, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, davem@davemloft.net X-BeenThere: virtualization@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Linux virtualization List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: virtualization-bounces@lists.linux-foundation.org Sender: "Virtualization" On Fri, Feb 17, 2023 at 01:53:55PM +0100, Jiri Pirko wrote: > Fri, Feb 17, 2023 at 01:22:01PM CET, mst@redhat.com wrote: > >On Fri, Feb 17, 2023 at 01:15:47PM +0100, Jiri Pirko wrote: > >> From: Jiri Pirko > >> > >> virtio_net_hdr_from_skb() fills up hdr_len to skb_headlen(skb). > >> > >> Virtio spec introduced a feature VIRTIO_NET_F_GUEST_HDRLEN which when > >> set implicates that the driver provides the exact size of the header. > >> > >> The driver already complies to fill the correct value. Introduce the > >> feature and advertise it. > >> > >> Signed-off-by: Jiri Pirko > > > >Could you add a bit of motivation just for the record? > >Does this improve performance for some card? By how much? > >Expected to help some future card? > > I can get that info, but isn't that rather something to be appended to > the virtio-spec patch? I mean, the feature is there, this is just > implementing it in one driver. It is more like using it in the driver. It's not like we have to use everything - it could be useful for e.g. dpdk but not linux. Implementing it in the Linux driver has support costs - for example what if there's a bug and sometimes the length is incorrect? We'll be breaking things. The patch was submitted by Marvell but they never bothered with using it in Linux. I guess they are using it for something else? CC Vitaly who put this in. > > > > >thanks! > > > > > >> --- > >> drivers/net/virtio_net.c | 6 ++++-- > >> include/uapi/linux/virtio_net.h | 1 + > >> 2 files changed, 5 insertions(+), 2 deletions(-) > >> > >> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c > >> index fb5e68ed3ec2..e85b03988733 100644 > >> --- a/drivers/net/virtio_net.c > >> +++ b/drivers/net/virtio_net.c > >> @@ -62,7 +62,8 @@ static const unsigned long guest_offloads[] = { > >> VIRTIO_NET_F_GUEST_UFO, > >> VIRTIO_NET_F_GUEST_CSUM, > >> VIRTIO_NET_F_GUEST_USO4, > >> - VIRTIO_NET_F_GUEST_USO6 > >> + VIRTIO_NET_F_GUEST_USO6, > >> + VIRTIO_NET_F_GUEST_HDRLEN > >> }; > >> > >> #define GUEST_OFFLOAD_GRO_HW_MASK ((1ULL << VIRTIO_NET_F_GUEST_TSO4) | \ > >> @@ -4213,7 +4214,8 @@ static struct virtio_device_id id_table[] = { > >> VIRTIO_NET_F_CTRL_MAC_ADDR, \ > >> VIRTIO_NET_F_MTU, VIRTIO_NET_F_CTRL_GUEST_OFFLOADS, \ > >> VIRTIO_NET_F_SPEED_DUPLEX, VIRTIO_NET_F_STANDBY, \ > >> - VIRTIO_NET_F_RSS, VIRTIO_NET_F_HASH_REPORT, VIRTIO_NET_F_NOTF_COAL > >> + VIRTIO_NET_F_RSS, VIRTIO_NET_F_HASH_REPORT, VIRTIO_NET_F_NOTF_COAL, \ > >> + VIRTIO_NET_F_GUEST_HDRLEN > >> > >> static unsigned int features[] = { > >> VIRTNET_FEATURES, > >> diff --git a/include/uapi/linux/virtio_net.h b/include/uapi/linux/virtio_net.h > >> index b4062bed186a..12c1c9699935 100644 > >> --- a/include/uapi/linux/virtio_net.h > >> +++ b/include/uapi/linux/virtio_net.h > >> @@ -61,6 +61,7 @@ > >> #define VIRTIO_NET_F_GUEST_USO6 55 /* Guest can handle USOv6 in. */ > >> #define VIRTIO_NET_F_HOST_USO 56 /* Host can handle USO in. */ > >> #define VIRTIO_NET_F_HASH_REPORT 57 /* Supports hash report */ > >> +#define VIRTIO_NET_F_GUEST_HDRLEN 59 /* Guest provides the exact hdr_len value. */ > >> #define VIRTIO_NET_F_RSS 60 /* Supports RSS RX steering */ > >> #define VIRTIO_NET_F_RSC_EXT 61 /* extended coalescing info */ > >> #define VIRTIO_NET_F_STANDBY 62 /* Act as standby for another device > >> -- > >> 2.39.0 > > _______________________________________________ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization