> -----Original Message----- > From: Jakub Kicinski <kuba@xxxxxxxxxx> > Sent: Thursday, January 23, 2020 11:59 AM > To: Haiyang Zhang <haiyangz@xxxxxxxxxxxxx> > Cc: sashal@xxxxxxxxxx; linux-hyperv@xxxxxxxxxxxxxxx; netdev@xxxxxxxxxxxxxxx; > KY Srinivasan <kys@xxxxxxxxxxxxx>; Stephen Hemminger > <sthemmin@xxxxxxxxxxxxx>; olaf@xxxxxxxxx; vkuznets > <vkuznets@xxxxxxxxxx>; davem@xxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx > Subject: Re: [PATCH V3,net-next, 1/2] hv_netvsc: Add XDP support > > On Wed, 22 Jan 2020 09:23:33 -0800, Haiyang Zhang wrote: > > This patch adds support of XDP in native mode for hv_netvsc driver, > > and transparently sets the XDP program on the associated VF NIC as well. > > > > Setting / unsetting XDP program on synthetic NIC (netvsc) propagates > > to VF NIC automatically. Setting / unsetting XDP program on VF NIC > > directly is not recommended, also not propagated to synthetic NIC, and > > may be overwritten by setting of synthetic NIC. > > > > The Azure/Hyper-V synthetic NIC receive buffer doesn't provide > > headroom for XDP. We thought about re-use the RNDIS header space, but > > it's too small. So we decided to copy the packets to a page buffer for > > XDP. And, most of our VMs on Azure have Accelerated Network (SRIOV) > > enabled, so most of the packets run on VF NIC. The synthetic NIC is > > considered as a fallback data-path. So the data copy on netvsc won't > > impact performance significantly. > > > > XDP program cannot run with LRO (RSC) enabled, so you need to disable > > LRO before running XDP: > > ethtool -K eth0 lro off > > > > XDP actions not yet supported: > > XDP_REDIRECT > > > > Signed-off-by: Haiyang Zhang <haiyangz@xxxxxxxxxxxxx> > > > > --- > > Changes: > > v3: Minor code and comment updates. > > v2: Added XDP_TX support. Addressed review comments. > > How does the locking of the TX path work? You seem to be just calling the > normal xmit method, but you don't hold the xmit queue lock, so the stack can > start xmit concurrently, no? The netvsc and vmbus can handle concurrent transmits, except the msd (Multi-Send Data) field which can only be used by one queue. I already added a new flag to netvsc_send(), so packets from XDP_TX won't use the msd. Thanks, - Haiyang
