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

[Ben Pfaff]

It doesn't sound like you have a bottleneck, if CPU is less than 10%, so
I don't understand the question.

On Fri, Jul 24, 2015 at 09:42:05AM -0700, Xuemei Liu wrote:
> Hi, Ben,
> 
> I have one follow-up question. I setup a topology with 12 hosts and 12
> switches in Mininet. The hosts (acting as the packets generator to the
> network) should send packets around 30 pps in order to make the switches
> not drop packets. However, I find that the CPU/MEM usage of ovs-vswitchd is
> not high (both < 10%). According to your experience, where do you think is
> the bottleneck? How can I improve the performance of packet processing
> speed in userspace in Mininet?
> 
> Thanks,
> Xuemei
> 
> On Fri, Jul 24, 2015 at 9:30 AM, Xuemei Liu <lxuemei3000 at gmail.com> wrote:
> 
> > Thanks very much Ben.
> >
> > On Fri, Jul 24, 2015 at 9:25 AM, Ben Pfaff <blp at nicira.com> wrote:
> >
> >> Any SLOW_* constant indicates why a packet can't be processed in the
> >> fast path (e.g. in the kernel).  Such packets always have to be handled
> >> in userspace.  Thus, tagging all flow translations with any SLOW_*
> >> constant causes them all to be sent to userspace.
> >>
> >> On Thu, Jul 23, 2015 at 05:07:58PM -0700, Xuemei Liu wrote:
> >> > 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;
> >> > > > > > >>
> >> > > > > > >
> >> > > > > > >
> >> > > > >
> >> > >
> >>
> >
> >