From: Jakub Kicinski
> Sent: 25 August 2017 20:34
>
> On Fri, 25 Aug 2017 08:24:49 -0700, Jacob Keller wrote:
> > Under some circumstances, such as with many stacked devices, it is
> > possible that dev_hard_start_xmit will bundle many packets together, and
> > mark them all with xmit_more.
>
> Excuse my ignorance but what are those stacked devices? Could they
> perhaps be fixed somehow? My intuition was that long xmit_more
> sequences can only happen if NIC and/or BQL are back pressuring, and
> therefore we shouldn't be seeing a long xmit_more "train" arriving at
> an empty device ring...
I also suspect that the packets could be coming from multiple sources.
So getting the sources to limit the number of packets with XMIT_MORE
set won't really solve any problem.
At some point the driver for the physical device will have to give it
a kick to start the transmits.
On the systems I've got (desktop x86) PCIe writes aren't really very
expensive.
Reads are a different matter entirely (2us into our fpga target).
David.
