Re: [dpdk-dev] [PATCH v2] librte_pmd_packet: add PMD for AF_PACKET-based virtual devices

["John W. Linville" <linville@tuxdriver.com>]

On Tue, Jul 15, 2014 at 03:40:56PM +0000, Zhou, Danny wrote:
> 
> > -----Original Message-----
> > From: John W. Linville [mailto:linville@tuxdriver.com]
> > Sent: Tuesday, July 15, 2014 10:01 PM
> > To: Neil Horman
> > Cc: Zhou, Danny; dev@dpdk.org
> > Subject: Re: [dpdk-dev] [PATCH v2] librte_pmd_packet: add PMD for
> > AF_PACKET-based virtual devices
> > 
> > On Tue, Jul 15, 2014 at 08:17:44AM -0400, Neil Horman wrote:
> > > On Tue, Jul 15, 2014 at 12:15:49AM +0000, Zhou, Danny wrote:
> > > > According to my performance measurement results for 64B small
> > > > packet, 1 queue perf. is better than 16 queues (1.35M pps vs. 0.93M
> > > > pps) which make sense to me as for 16 queues case more CPU cycles
> > > > (16 queues' 87% vs. 1 queue' 80%) in kernel land needed for
> > > > NAPI-enabled ixgbe driver to switch between polling and interrupt
> > > > modes in order to service per-queue rx interrupts, so more context
> > > > switch overhead involved. Also, since the
> > > > eth_packet_rx/eth_packet_tx routines involves in two memory copies
> > > > between DPDK mbuf and pbuf for each packet, it can hardly achieve
> > > > high performance unless packet are directly DMA to mbuf which needs ixgbe
> > driver to support.
> > >
> > > I thought 16 queues would be spread out between as many cpus as you
> > > had though, obviating the need for context switches, no?
> > 
> > I think Danny is testing the single CPU case.  Having more queues than CPUs
> > probably does not provide any benefit.
> > 
> > It would be cool to hack the DPDK memory management to work directly out of the
> > mmap'ed AF_PACKET buffers.  But at this point I don't have enough knowledge of
> > DPDK internals to know if that is at all reasonable...
> > 
> > John
> > 
> > P.S.  Danny, have you run any performance tests on the PCAP driver?
> 
> No, I do not have PCAP driver performance results in hand. But I remember it is less than
> 1M pps for 64B.

Cool, good info...thanks!

-- 
John W. Linville		Someday the world will need a hero, and you
linville@tuxdriver.com			might be all we have.  Be ready.