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Date:      Sat, 16 Apr 2011 15:49:10 -0500
From:      Alex Anagnos <woodshop2300@gmail.com>
To:        Julian Elischer <julian@freebsd.org>
Cc:        freebsd-emulation@freebsd.org
Subject:   Re: Networking frame loss in transmission
Message-ID:  <608E001D-14AF-4025-80D0-58369BE95773@gmail.com>
In-Reply-To: <4DA9FBCE.2060106@freebsd.org>
References:  <20110416120030.457A510656DF@hub.freebsd.org> <4DA9FBCE.2060106@freebsd.org>

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I sometime see arps int the beginning of the captures.
They are followed by the the frames, sometimes the error happens =
sometime not.
Other times i see arps in the middle of the stream, with nothing wrong.

I'm running this test with short 20-30 second gaps between them (to =
reset captures)..
So the arp table is not even expiring between runs. So on shorter run, i =
don't see arps at all, and the problem still sometimes occurs..


I have not tried a FreeBSD guest, but i don't think the guest is the =
issue here.
I'v taken the same linux Guest, and run it temporally on a Windows host, =
and the problem never manifests.


On Apr 16, 2011, at 3:27 PM, Julian Elischer wrote:

>=20
>> Message: 2
>> Date: Fri, 15 Apr 2011 18:57:19 -0500
>> From: Alex Anagnos<woodshop2300@gmail.com>
>> Subject: Networking frame loss in transmission
>> To: freebsd-emulation@freebsd.org
>> Message-ID:<BANLkTik92Eg0hrHsaK0J8yh3vibuyRDZew@mail.gmail.com>
>> Content-Type: text/plain; charset=3DISO-8859-1
>>=20
>> FreeBSD 8.0-RELEASE w/ VirtualBox 3.2.12.
>>=20
>> The setup is a small application in a Guest OS that is sending UDP
>> Ethernet frames.
>> I Am capturing on FreeBSD on the device with both Wireshark, and a
>> custom written program that uses BPF zero copy.
>>=20
>> What i'm seeing is that when the application send data that is beyond
>> the MTU the data is fragmented.
>> However, sometimes, the first few fragments never show up in the
>> capture, and indeed the receiving app never gets the message
>> (reassembly fails).
>=20
> maybe it was waiting for arp?
>> So when I call send with an 8192 payload, i see,  frames 1 and 2 go
>> missing, but 3, 4, and , 5 get out fine. (1500 MTU)
> do you see an arp reply wbetween 2 and 3?
>=20
>> When calling send 2 times in rapid succession, all fragments of the
>> first send go missing as well as 1, and 2 of the 2nd send. 3, 4, and =
5
>> get out fine.
>> When calling send 3 times in rapid succession, all fragments of send =
1
>> &  2 get lost as well as fragment 1&  2 of the 3rd send. Frags 3, 4,
>> and 5 are fine.
>=20
> makes arp less likely but not impossible.
>> When sending this at like 1 Message per second, things occasionally =
don't work.
>> When going at 3000FPS, it has so far always been the first few =
frames,
>> after that the rest of the stream gets through ok almost like the
>> driver has to warm up or something..
>>=20
>> The issue happens sending from both a Linux guest and from a Windows =
Guest.
>> The issue does not care about the speed of the traffic, it happens at
>> 1FPS and at 3000FPS.
> have you tried a freebsd guest? at least we can debug that.. :-)
>=20
>> The issue does seam to occur less often the smaller the message sent.
>> When the message does not require fragmentation I have not seen the
>> issue happen but i'm not going to guarantee it does not happen.
>>=20
>> The problem happens using Bridged, VDE, and Host-Only.
>> The problem happens using the FastPCI driver, intel e1000, and =
para-virtualized.
>> The problem happens with any number of the above 3 combos.
>>=20
>> The problem happens in Version 3.2.6 and inversion 3.2.12.
>>=20
>> The problem looks to be somewhere in the VirtualBox box code, or =
maybe
>> in the VirtualBox kernel module integration with FreeBSD
>=20
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