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

Thu Aug 6 21:46:03 UTC 2015

Hi, all,

I have one followup question about performance of ovs. I am running my
experiment (12 switches and 12 hosts in Mininet) with a 32 core machine. I
track the CPU/MEM usage of all threads of ovs-vswitchd
(handler/revalidator), all of them are below 60%. However, I find that
there are packets lost in the ovs switches. I am wondering whether that's
because the buffer size of ports is not big enough (How can I configure the
buffer size)?  Or the queue size between kernel and userspace, as I
configure to send all packets from kernel space to userspace (according to
Ben's advice).

Thanks,
Xuemei

On Sat, Jul 25, 2015 at 6:15 PM, Xuemei Liu <lxuemei3000 at gmail.com> wrote:

> I found that problem in the VM of my pc. When I run the experiments on one
> physical server, the CPU usage is not that low.
>
> On Fri, Jul 24, 2015 at 1:24 PM, Ben Pfaff <blp at nicira.com> wrote:
>
>> 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;
>> > >> > > > > > >>
>> > >> > > > > > >
>> > >> > > > > > >
>> > >> > > > >
>> > >> > >
>> > >>
>> > >
>> > >
>>
>
>
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