[ovs-discuss] How to send all packets to userspace?

Ben Pfaff blp at nicira.com
Thu Jul 23 23:46:57 UTC 2015


Well, yes, there are performance problems, as I predicted.

On Thu, Jul 23, 2015 at 04:42:17PM -0700, Xuemei Liu wrote:
> Let me try to describe it. Suppose the topology is h1-s1-h2, where h1, h2
> are hosts, and s1 is the ovs switch. I add policy in s1 to forward packets
> with dstip of h2 to h2. Then I test in two scenarios.
> 1. h1 sends 9 packets (3 packet for each of 3 different flows) to h2. With
> your methods, userspace in s1 can accept all the packets, and h2 can
> receive all the 9 packets. Work perfect.
> 2. h1 sends 10000 packets to h2. In this case, h2 receives the same packets
> as userspace in s1 does. However, the number of packets received is much
> less than 10000. Which means many packets are lost in s1.
> Is this clear now?
> 
> Thanks,
> Xuemei
> 
> On Thu, Jul 23, 2015 at 4:18 PM, Ben Pfaff <blp at nicira.com> wrote:
> 
> > That's too vague for me to guess.  What packets are getting lost?
> >
> > On Thu, Jul 23, 2015 at 04:10:14PM -0700, Xuemei Liu wrote:
> > > Hi, Ben,
> > >
> > > I tried your method, but the switch seems to drop some packets, as it
> > does
> > > not output the expected packets that I forward to send to it. Any advice?
> > >
> > > Thanks,
> > > Xuemei
> > >
> > > On Thu, Jul 23, 2015 at 10:19 AM, Xuemei Liu <lxuemei3000 at gmail.com>
> > wrote:
> > >
> > > > Hi, Ben,
> > > >
> > > > Thanks for your response.
> > > > "You realize that this will be terrible for performance, right?"
> > > > In fact, I have not got all packets sent to user space. That is the
> > > > problem I am facing now. I think performance might be another problem
> > after
> > > > I can receive all packet in user space.
> > > >
> > > > Thanks,
> > > > Xuemei
> > > >
> > > > On Thu, Jul 23, 2015 at 10:13 AM, Ben Pfaff <blp at nicira.com> wrote:
> > > >
> > > >> On Thu, Jul 23, 2015 at 10:04:23AM -0700, Xuemei Liu wrote:
> > > >> > I am new to ovs, and I am trying to send all packets from kernel
> > space
> > > >> to
> > > >> > user space. I comment the "unlikely(!flow)" in datapath/datapath.c.
> > > >> > However, it seems I just receive the first packet of each flow (the
> > > >> first
> > > >> > packet that match one forwarding rule in the bridge) in user space.
> > > >> Could
> > > >> > anyone tell me why? and is there other way to achieve my goal?
> > > >>
> > > >> You realize that this will be terrible for performance, right?
> > > >>
> > > >> It's kind of a waste to modify the kernel module for this.  I'd just
> > > >> modify userspace to send all packets to userspace, something like
> > this:
> > > >>
> > > >> diff --git a/ofproto/ofproto-dpif-xlate.c
> > b/ofproto/ofproto-dpif-xlate.c
> > > >> index 52395a7..a98406a 100644
> > > >> --- a/ofproto/ofproto-dpif-xlate.c
> > > >> +++ b/ofproto/ofproto-dpif-xlate.c
> > > >> @@ -4777,7 +4777,7 @@ xlate_actions(struct xlate_in *xin, struct
> > > >> xlate_out *xout)
> > > >>
> > > >>      ctx.xin = xin;
> > > >>      ctx.xout = xout;
> > > >> -    ctx.xout->slow = 0;
> > > >> +    ctx.xout->slow = SLOW_ACTION;
> > > >>      ctx.xout->has_learn = false;
> > > >>      ctx.xout->has_normal = false;
> > > >>      ctx.xout->has_fin_timeout = false;
> > > >>
> > > >
> > > >
> >



More information about the discuss mailing list