Re: [dpdk-dev] [RFC] ethdev: introduce shared Rx queue

["Xueming(Steven) Li" <xuemingl@nvidia.com>]

Hi Andrew,

> -----Original Message-----
> From: Andrew Rybchenko <andrew.rybchenko@oktetlabs.ru>
> Sent: Wednesday, July 28, 2021 3:57 PM
> To: Xueming(Steven) Li <xuemingl@nvidia.com>
> Cc: dev@dpdk.org; Slava Ovsiienko <viacheslavo@nvidia.com>; NBU-Contact-Thomas Monjalon <thomas@monjalon.net>; Ferruh
> Yigit <ferruh.yigit@intel.com>
> Subject: Re: [RFC] ethdev: introduce shared Rx queue
> 
> On 7/27/21 6:42 AM, Xueming Li wrote:
> > In eth PMD driver model, each RX queue was pre-loaded with mbufs for
> > saving incoming packets. When number of SF or VF scale out in a switch
> > domain, the memory consumption became significant. Most important,
> > polling all ports leads to high cache miss, high latency and low
> > throughput.
> >
> > To save memory and speed up, this patch introduces shared RX queue.
> > Ports with same configuration in a switch domain could share RX queue
> > set by specifying offloading flag RTE_ETH_RX_OFFLOAD_SHARED_RXQ.
> > Polling a member port in shared RX queue receives packets for all member ports.
> > Source port is identified by mbuf->port.
> >
> > Queue number of ports in shared group should be identical. Queue index
> > is 1:1 mapped in shared group.
> >
> > Shared RX queue is supposed to be polled on same thread.
> >
> > Multiple groups is supported by group ID.
> >
> > Signed-off-by: Xueming Li <xuemingl@nvidia.com>
> 
> It looks like it could be useful to artificial benchmarks, but absolutely useless for real life. SFs and VFs are used by VMs (or containers?)
> to have its own part of HW. If so, SF or VF Rx and Tx queues live in a VM and cannot be shared.

Thanks for looking at this! Agree, SF and VF can't be shared.

> 
> Sharing makes sense for representors, but it is not mentioned in the description.

Yes, the major target is representors, ports in same switch domain, I'll emphasis this in next version.