Lost ping responses

Lost ping responses

[David Laight]

As part of some other testing I've been saturating a point to point
100M ethernet links with 3 flood pings of 60k messages.
The response time is then 17-20ms, and there are no missing responses.
If I also do a 'normal' ping, that one sees a 25% packet loss.

ifconfig doesn't show any errors, and the tx and rx counts match
between the systems. All the packets seem to get lost on the system
that is responding to the ping requests.

Any ideas how to find out where the discards are happening?
It might just be somewhere that would affect other traffic flows.

Both systems are Intel i7 - so no shortage of cpu power or memory.
The pings are being sent from a PCIe e1000e card, and reflected
by a USB smsx95xx one.
(I was just loading the USB wire, nothing odd happened during the test.)

	David

Re: Lost ping responses

[Jamal Hadi Salim]

On 08/19/14 06:28, David Laight wrote:

> Any ideas how to find out where the discards are happening?
> It might just be somewhere that would affect other traffic flows.
>

netstat -s

cat /proc/net/softnet_stat

are some points to look at.

cheers,
jamal

RE: Lost ping responses

[David Laight]

From: Jamal Hadi Salim

> > Any ideas how to find out where the discards are happening?
> > It might just be somewhere that would affect other traffic flows.
> 
> netstat -s

Thanks - 'Ip: outgoing packets dropped' increments for every lost response.

Next step is to work out what that means...

	David

Re: Lost ping responses

[Cong Wang]

On Tue, Aug 19, 2014 at 4:35 AM, David Laight <David.Laight@aculab.com> wrote:
> From: Jamal Hadi Salim
>
>> > Any ideas how to find out where the discards are happening?
>> > It might just be somewhere that would affect other traffic flows.
>>
>> netstat -s
>
> Thanks - 'Ip: outgoing packets dropped' increments for every lost response.
>
> Next step is to work out what that means...
>

Try dropwatch, it should give you better hints.

RE: Lost ping responses

[David Laight]

From: Cong Wang
> On Tue, Aug 19, 2014 at 4:35 AM, David Laight <David.Laight@aculab.com> wrote:
> > From: Jamal Hadi Salim
> >
> >> > Any ideas how to find out where the discards are happening?
> >> > It might just be somewhere that would affect other traffic flows.
> >>
> >> netstat -s
> >
> > Thanks - 'Ip: outgoing packets dropped' increments for every lost response.
> >
> > Next step is to work out what that means...
> >
> 
> Try dropwatch, it should give you better hints.

That involves finding/compiling a version that will run on ubuntu 13.10 server.
And working out which extra ubuntu packages it needs to work.
On a system I've built the sources on (after fixing LDLIBS) I get the
error 'Unable to find NET_DM family' - whatever that means.
but that isn't the system dropping packets.

	David