On Nov 21, 2016, at 4:48 AM, Damjan Marion (damarion) [off-list ref] wrote:


Hi,

Currently in VPP we do memcpy of whole packet when we need to do 
replication as we cannot know if specific buffer is transmitted
from tx ring before we update it again (i.e. l2 header rewrite).

Unless there is already a way to address this issue in DPDK which I’m not aware
of my proposal is that we provide mechanism for polling TX ring 
for consumed buffers. This can be either completely new API or 
extension of rte_etx_tx_burst (i.e. special case when nb_pkts=0).

This will allows us to start polling tx ring when we expect some 
mbuf back, instead of waiting for next tx burst (which we don’t know
when it will happen) and hoping that we will reach free_threshold soon.

+1

In Pktgen I have the problem of not being able to reclaim all of the TX mbufs to update them for the next set of packets to send. I know this is not a common case, but I do see the case where the application needs its mbufs freed off the TX ring. Currently you need to have at least a TX ring size of mbufs on hand to make sure you can send to a TX ring. If you allocate too few you run into a deadlock case as the number of mbufs  on a TX ring does not hit the flush mark. If you are sending to multiple TX rings on the same numa node from the a single TX pool you have to understand the total number of mbufs you need to have allocated to hit the TX flush on each ring. Not a clean way to handle the problems as you may have limited memory or require some logic to add more mbufs for dynamic ports.

Anyway it would be great to require a way to clean up the TX done ring, using nb_pkts == 0 is the simplest way, but a new API is fine too.

Any thoughts?

Thanks,

Damjan

Regards,
Keith