Re: [dpdk-dev] [PATCH v4] net/af_packet: reinsert the stripped vlan tag
From: Ferruh Yigit <hidden>
Date: 2021-09-30 08:14:55
On 9/29/2021 3:08 PM, Tudor Cornea wrote:
quoted hunk ↗ jump to hunk
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 <redacted> --- v4: * Updated the af_packet documentation 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 | 5 +++++ doc/guides/rel_notes/release_21_11.rst | 4 ++++ drivers/net/af_packet/rte_eth_af_packet.c | 12 ++++++++++++ 3 files changed, 21 insertions(+)diff --git a/doc/guides/nics/af_packet.rst b/doc/guides/nics/af_packet.rst index efd6f1c..c87310b 100644 --- a/doc/guides/nics/af_packet.rst +++ b/doc/guides/nics/af_packet.rst@@ -65,3 +65,8 @@ 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 +--------------------------------------------- + +Af_packet PMD now works with VLAN's on Linux
Thanks Tudor. I see this is suggested by Stephen, but I think 'now' is confusing in the driver guide. Also driver was already working with VLAN, the change is VLAN is not force stripped anymore. I think following part from your previous version is better, what do you think something like following? " The PMD will re-insert the VLAN tag transparently to the packet if the kernel strips it, as long as the ``DEV_RX_OFFLOAD_VLAN_STRIP`` is not enabled by application. "
quoted hunk ↗ jump to hunk
diff --git a/doc/guides/rel_notes/release_21_11.rst b/doc/guides/rel_notes/release_21_11.rst index ad7c1af..095fd5b 100644 --- a/doc/guides/rel_notes/release_21_11.rst +++ b/doc/guides/rel_notes/release_21_11.rst@@ -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. +
I think change in the default behavior is more important in the release notes, again what do you think to have your following update here: " Default VLAN strip behavior changed. If previously, the vlan tag was stripped, if the application now requires the same behavior, it will need to configure ``DEV_RX_OFFLOAD_VLAN_STRIP``. "