[ovs-dev] [PATCH v3] Documentation: add notes for TSO & i40e
fbl at sysclose.org
Mon Jan 20 14:45:29 UTC 2020
On Mon, Jan 20, 2020 at 01:09:36PM +0000, Ciara Loftus wrote:
> When using TSO in OVS-DPDK with an i40e device, the following
> patch is required for DPDK, which fixes an issue on the TSO path:
> Document this as a limitation until a DPDK release with the fix
> included is supported by OVS.
> Also, document best known methods for performance tuning when
> testing TSO with the tool iperf.
> Fixes: 29cf9c1b3b9c ("userspace: Add TCP Segmentation Offload support")
> Signed-off-by: Ciara Loftus <ciara.loftus at intel.com>
> Acked-by: Flavio Leitner <fbl at sysclose.org>
> - Added Fixes tag
> - Removed unwanted manpages.mk change
> - rebased to master
> - changed patch links from net-next tree to patchwork
> Documentation/topics/userspace-tso.rst | 27 ++++++++++++++++++++++++++
> 1 file changed, 27 insertions(+)
> diff --git a/Documentation/topics/userspace-tso.rst b/Documentation/topics/userspace-tso.rst
> index 893c64839..94eddc0b2 100644
> --- a/Documentation/topics/userspace-tso.rst
> +++ b/Documentation/topics/userspace-tso.rst
> @@ -96,3 +96,30 @@ datapath must support TSO or packets using that feature will be dropped
> on ports without TSO support. That also means guests using vhost-user
> in client mode will receive TSO packet regardless of TSO being enabled
> or disabled within the guest.
> +When the NIC performing the segmentation is using the i40e DPDK PMD, a fix
> +must be included in the DPDK build, otherwise TSO will not work. The fix can
> +be found on `DPDK patchwork`__.
> +__ https://patches.dpdk.org/patch/64136/
> +This fix is expected to be included in the 19.11.1 release. When OVS migrates
> +to this DPDK release, this limitation can be removed.
> +Performance Tuning
> +iperf is often used to test TSO performance. Care needs to be taken when
> +configuring the environment in which the iperf server process is being run.
> +Since the iperf server uses the NIC's kernel driver, IRQs will be generated.
> +By default with some NICs eg. i40e, the IRQs will land on the same core as that
> +which is being used by the server process, provided the number of NIC queues is
> +greater or equal to that lcoreid. This causes contention between the iperf
> +server process and the IRQs. For optimal performance, it is suggested to pin
> +the IRQs to their own core. To change the affinity associated with a given IRQ
> +number, you can 'echo' the desired coremask to the file
> +For more on SMP affinity, refer to the `Linux kernel documentation`__.
> +__ https://www.kernel.org/doc/Documentation/IRQ-affinity.txt
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