On Thu, Jun 11, 2015 at 12:45:10PM +0000, Daniele Di Proietto wrote:
>
>
> On 11/06/2015 04:25, "Flavio Leitner" <f...@sysclose.org> wrote:
>
> >On Wed, Jun 10, 2015 at 03:13:21PM +0000, Daniele Di Proietto wrote:
> >>
> >>
> >> On 10/06/2015 12:48, "Gray, Mark D" <mark.d.g...@intel.com> wrote:
> >> >
> >> >The vhost port won't generate an RSS hash because it is a virtual NIC.
> >> >
> >> >>
> >> >
> >> >> It doesn't cause a problem, just make the pkt fall into a slow path,
> >> >>should we
> >> >
> >> >> fix it?
> >>
> >> Thanks for investigating this. We should definitely fix it.
> >>
> >> >
> >> >> The flag ol_flags may be useful for OVS or let DPDK fix this in vhost
> >> >>rcv.
> >> >
> >> >
> >> >
> >> >How do you propose that this would work? The RSS would still have to be
> >> >
> >> >generated in software.
> >> >
> >> >>
> >>
> >> A simple solution would be to reset the RSS hash inside
> >> netdev_dpdk_vhost_rxq_recv(). Other netdev providers that do not
> >>support
> >> reading the RSS hash (netdev-linux, netdev-bsd) call
> >> dp_packet_set_rss_hash(pkt, 0) on every received packet.
> >>
> >> This would probably have a small impact on performance, but it's better
> >> than trashing the exact match cache.
> >>
> >> I don't believe there's anything that DPDK can do here (like resetting
> >>the
> >> hash when the packet is freed), but please correct me if I'm wrong.
> >>
> >> Thoughts?
> >
> >I think Dongjun is right and we should use ol_flags.
> >Something like this:
> >
> >diff --git a/lib/dp-packet.h b/lib/dp-packet.h
> >index e4c2593..ad315d1 100644
> >--- a/lib/dp-packet.h
> >+++ b/lib/dp-packet.h
> >@@ -518,7 +518,12 @@ static inline uint32_t
> > dp_packet_get_rss_hash(struct dp_packet *p)
> > {
> > #ifdef DPDK_NETDEV
> >- return p->mbuf.hash.rss;
> >+ if (p->mbuf.ol_flags & PKT_RX_RSS_HASH) {
> >+ return p->mbuf.hash.rss;
> >+ }
> >+ else {
> >+ return 0;
> >+ }
> > #else
> > return p->rss_hash;
> > #endif
> >
> >
> >I haven't tested that but rte_vhost_dequeue_burst() does
> >ol_flags = 0, so this would be a generic solution for all
> >dpdk devices.
> >
> >Thoughts?
> >
> >fbl
>
> This seems a much better solution. I had no idea that ol_flags
> included PKT_RX_RSS_HASH.
>
> Unfortunately, I tested it and it appears that ixgbe_recv_pkts_vec()
> is not setting the flag correctly (it is documented in the comments).
> Other ideas?
The ixgbe_recv_pkts_vec() should at least set ol_flags to zero
because it isn't providing a valid hash and what you get is garbage
from the OVS stack. Is that what you are seeing?
If so, ixgbe_recv_pkts_vec() needs to set ol_flags to zero. This will
fix for every user of dpdk, not just OVS.
As a possible workaround for OVS we could fix dp_netdev_process_rxq_port()
to memset(0) the packets mbufs array which should be faster than loop
through the array and set fields to zero.
fbl
_______________________________________________
dev mailing list
dev@openvswitch.org
http://openvswitch.org/mailman/listinfo/dev
