[v3] net/af_packet: reinsert the stripped vlan tag
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Commit Message
The af_packet pmd driver binds to a raw socket and allows
sending and receiving of packets through the kernel.
Since commit [1], the kernel strips the vlan tags early in
__netif_receive_skb_core(), so we receive untagged packets while
running with the af_packet pmd.
Luckily for us, the skb vlan-related fields are still populated from the
stripped vlan tags, so we end up having all the information
that we need in the mbuf.
Having the pmd driver support DEV_RX_OFFLOAD_VLAN_STRIP allows the
application to control the desired vlan stripping behavior,
until we have a way to describe offloads that can't be disabled by
pmd drivers.
This patch will cause a change in the default way that the af_packet
pmd treats received vlan-tagged frames. While previously, the
application was required to check the PKT_RX_VLAN_STRIPPED flag, after
this patch, the pmd will re-insert the vlan tag transparently to the
user, unless the DEV_RX_OFFLOAD_VLAN_STRIP is enabled in
rxmode.offloads.
I've attempted a preliminary benchmark to understand if the change could
cause a sizable performance hit.
Setup:
Two virtual machines running on top of an ESXi hypervisor
Tx: DPDK app (running on top of vmxnet3 PMD)
Rx: af_packet (running on top of a kernel vmxnet3 interface)
Packet size :68 (packet contains a vlan tag)
Rates:
Tx - 1.419 Mpps
Rx (without vlan insertion) - 1227636 pps
Rx (with vlan insertion) - 1220081 pps
At a first glance, we don't seem to have a large degradation in terms of packet rate
[1] https://github.com/torvalds/linux/commit/bcc6d47903612c3861201cc3a866fb604f26b8b2
Signed-off-by: Tudor Cornea <tudor.cornea@gmail.com>
---
v3:
* Updated release note and documentation
* Updated commit with performance measurements
v2:
* Added DEV_RX_OFFLOAD_VLAN_STRIP to rxmode->offloads
---
doc/guides/nics/af_packet.rst | 38 +++++++++++++++++++++++++++++++
doc/guides/rel_notes/release_21_11.rst | 4 ++++
drivers/net/af_packet/rte_eth_af_packet.c | 12 ++++++++++
3 files changed, 54 insertions(+)
Comments
On Fri, 24 Sep 2021 14:44:45 +0300
Tudor Cornea <tudor.cornea@gmail.com> wrote:
> +Features and Limitations of the af_packet PMD
> +---------------------------------------------
> +
> +Since the following commit, the Linux kernel strips the vlan tag
> +
> +.. code-block:: console
> +
> + commit bcc6d47903612c3861201cc3a866fb604f26b8b2
> + Author: Jiri Pirko <jpirko@xxxxxxxxxx>
> + Date: Thu Apr 7 19:48:33 2011 +0000
> +
> + net: vlan: make non-hw-accel rx path similar to hw-accel
> +
> +Running on such a kernel results in receiving untagged frames while using
> +the af_packet PMD. Fortunately, the stripped information is still available
> +for use in ``mbuf->vlan_tci``, and applications could check ``PKT_RX_VLAN_STRIPPED``.
> +
> +However, we currently don't have a way to describe offloads which can't be
> +disabled by PMDs, and this creates an inconsistency with the way applications
> +expect the PMD offloads to work, and requires them to be aware of which
> +underlying driver they use.
> +
> +Since release 21.11 the af_packet PMD will implement support for the
> +``DEV_RX_OFFLOAD_VLAN_STRIP`` offload, and users can control the desired vlan
> +stripping behavior.
> +
> +It's important to note that the default case will change. If previously,
> +the vlan tag was stripped, if the application now requires the same behavior,
> +it will need to configure ``rxmode.offloads`` with ``DEV_RX_OFFLOAD_VLAN_STRIP``.
> +
> +The PMD driver will re-insert the vlan tag transparently to the application
> +if the kernel strips it, as long as the ``DEV_RX_OFFLOAD_VLAN_STRIP`` is not
> +enabled.
This seems like the wrong place for this text.
It is not a new feature, it is a bug fix.
If you want to describe it as an enhancement, the text should be succinct and describe
the situation from user point of view. Something like:
Af_packet PMD now works with VLAN's on Linux
Thanks Stephen, for the suggestion
I've sent v4 of the patch, which adds the succinct description in the
af_packet documentation..
On Fri, 24 Sept 2021 at 18:11, Stephen Hemminger <stephen@networkplumber.org>
wrote:
> On Fri, 24 Sep 2021 14:44:45 +0300
> Tudor Cornea <tudor.cornea@gmail.com> wrote:
>
> > +Features and Limitations of the af_packet PMD
> > +---------------------------------------------
> > +
> > +Since the following commit, the Linux kernel strips the vlan tag
> > +
> > +.. code-block:: console
> > +
> > + commit bcc6d47903612c3861201cc3a866fb604f26b8b2
> > + Author: Jiri Pirko <jpirko@xxxxxxxxxx>
> > + Date: Thu Apr 7 19:48:33 2011 +0000
> > +
> > + net: vlan: make non-hw-accel rx path similar to hw-accel
> > +
> > +Running on such a kernel results in receiving untagged frames while
> using
> > +the af_packet PMD. Fortunately, the stripped information is still
> available
> > +for use in ``mbuf->vlan_tci``, and applications could check
> ``PKT_RX_VLAN_STRIPPED``.
> > +
> > +However, we currently don't have a way to describe offloads which can't
> be
> > +disabled by PMDs, and this creates an inconsistency with the way
> applications
> > +expect the PMD offloads to work, and requires them to be aware of which
> > +underlying driver they use.
> > +
> > +Since release 21.11 the af_packet PMD will implement support for the
> > +``DEV_RX_OFFLOAD_VLAN_STRIP`` offload, and users can control the
> desired vlan
> > +stripping behavior.
> > +
> > +It's important to note that the default case will change. If previously,
> > +the vlan tag was stripped, if the application now requires the same
> behavior,
> > +it will need to configure ``rxmode.offloads`` with
> ``DEV_RX_OFFLOAD_VLAN_STRIP``.
> > +
> > +The PMD driver will re-insert the vlan tag transparently to the
> application
> > +if the kernel strips it, as long as the ``DEV_RX_OFFLOAD_VLAN_STRIP``
> is not
> > +enabled.
>
> This seems like the wrong place for this text.
> It is not a new feature, it is a bug fix.
>
> If you want to describe it as an enhancement, the text should be succinct
> and describe
> the situation from user point of view. Something like:
>
> Af_packet PMD now works with VLAN's on Linux
>
>
@@ -65,3 +65,41 @@ framecnt=512):
.. code-block:: console
--vdev=eth_af_packet0,iface=tap0,blocksz=4096,framesz=2048,framecnt=512,qpairs=1,qdisc_bypass=0
+
+Features and Limitations of the af_packet PMD
+---------------------------------------------
+
+Since the following commit, the Linux kernel strips the vlan tag
+
+.. code-block:: console
+
+ commit bcc6d47903612c3861201cc3a866fb604f26b8b2
+ Author: Jiri Pirko <jpirko@xxxxxxxxxx>
+ Date: Thu Apr 7 19:48:33 2011 +0000
+
+ net: vlan: make non-hw-accel rx path similar to hw-accel
+
+Running on such a kernel results in receiving untagged frames while using
+the af_packet PMD. Fortunately, the stripped information is still available
+for use in ``mbuf->vlan_tci``, and applications could check ``PKT_RX_VLAN_STRIPPED``.
+
+However, we currently don't have a way to describe offloads which can't be
+disabled by PMDs, and this creates an inconsistency with the way applications
+expect the PMD offloads to work, and requires them to be aware of which
+underlying driver they use.
+
+Since release 21.11 the af_packet PMD will implement support for the
+``DEV_RX_OFFLOAD_VLAN_STRIP`` offload, and users can control the desired vlan
+stripping behavior.
+
+It's important to note that the default case will change. If previously,
+the vlan tag was stripped, if the application now requires the same behavior,
+it will need to configure ``rxmode.offloads`` with ``DEV_RX_OFFLOAD_VLAN_STRIP``.
+
+The PMD driver will re-insert the vlan tag transparently to the application
+if the kernel strips it, as long as the ``DEV_RX_OFFLOAD_VLAN_STRIP`` is not
+enabled.
+
+.. code-block:: console
+
+ port_conf.rxmode.offloads |= DEV_RX_OFFLOAD_VLAN_STRIP
@@ -66,6 +66,10 @@ New Features
* Added rte_flow support for dual VLAN insert and strip actions.
+* **Updated af_packet ethdev driver.**
+
+ * Added DEV_RX_OFFLOAD_VLAN_STRIP capability.
+
* **Updated Marvell cnxk crypto PMD.**
* Added AES-CBC SHA1-HMAC support in lookaside protocol (IPsec) for CN10K.
@@ -48,6 +48,7 @@ struct pkt_rx_queue {
struct rte_mempool *mb_pool;
uint16_t in_port;
+ uint8_t vlan_strip;
volatile unsigned long rx_pkts;
volatile unsigned long rx_bytes;
@@ -78,6 +79,7 @@ struct pmd_internals {
struct pkt_rx_queue *rx_queue;
struct pkt_tx_queue *tx_queue;
+ uint8_t vlan_strip;
};
static const char *valid_arguments[] = {
@@ -148,6 +150,9 @@ eth_af_packet_rx(void *queue, struct rte_mbuf **bufs, uint16_t nb_pkts)
if (ppd->tp_status & TP_STATUS_VLAN_VALID) {
mbuf->vlan_tci = ppd->tp_vlan_tci;
mbuf->ol_flags |= (PKT_RX_VLAN | PKT_RX_VLAN_STRIPPED);
+
+ if (!pkt_q->vlan_strip && rte_vlan_insert(&mbuf))
+ PMD_LOG(ERR, "Failed to reinsert VLAN tag");
}
/* release incoming frame and advance ring buffer */
@@ -302,6 +307,11 @@ eth_dev_stop(struct rte_eth_dev *dev)
static int
eth_dev_configure(struct rte_eth_dev *dev __rte_unused)
{
+ struct rte_eth_conf *dev_conf = &dev->data->dev_conf;
+ const struct rte_eth_rxmode *rxmode = &dev_conf->rxmode;
+ struct pmd_internals *internals = dev->data->dev_private;
+
+ internals->vlan_strip = !!(rxmode->offloads & DEV_RX_OFFLOAD_VLAN_STRIP);
return 0;
}
@@ -318,6 +328,7 @@ eth_dev_info(struct rte_eth_dev *dev, struct rte_eth_dev_info *dev_info)
dev_info->min_rx_bufsize = 0;
dev_info->tx_offload_capa = DEV_TX_OFFLOAD_MULTI_SEGS |
DEV_TX_OFFLOAD_VLAN_INSERT;
+ dev_info->rx_offload_capa = DEV_RX_OFFLOAD_VLAN_STRIP;
return 0;
}
@@ -448,6 +459,7 @@ eth_rx_queue_setup(struct rte_eth_dev *dev,
dev->data->rx_queues[rx_queue_id] = pkt_q;
pkt_q->in_port = dev->data->port_id;
+ pkt_q->vlan_strip = internals->vlan_strip;
return 0;
}