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

[Xuemei Liu]

Hi, Ben,

After I decreased the sending rate at h1, I find s1 userspace/h2 can
receive all packets. What does SLOW_ACTION mean? Why this will make the
packets forwarded from kernel space to user space?

Thanks,
Xuemei

On Thu, Jul 23, 2015 at 4:46 PM, Ben Pfaff <blp at nicira.com> wrote:

> 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;
> > > > >>
> > > > >
> > > > >
> > >
>
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