[Click] FromDevice (OS-X) buffering up packets...

[Giorgio Calarco]

hi all,

having bursts of packets and increased jitter does not only depends on
the Click itself, but also from the queueing at the NIC FIFO. The PCI
bus is indeed fair (in the sense that it serves each peripheral
with a token passing policy), but once the peripheral acquires
access onto the bus, it's not time-limited in any way. If the bus
occupancy probability is high, for any reason, the NICs tend to accumulate
packets in their internal FIFO and once they can start the DMA
transfer, they move all the packets back-to-back, generating
a burst. I 'm not sure if this is your case (which hardware are you using ?
could the bus possibly be close to saturation ?),
 anyway, you can find more details in one of the second (?) chapther
of my past PhD
thesis (it's published on the Click site - Publications).
Hope it can help in some way.

Ciao, Giorgio

On Tue, Jul 20, 2010 at 6:55 PM,  <rchertov at cs.ucsb.edu> wrote:
> On 5:25 pm 07/19/10 <rchertov at cs.ucsb.edu> wrote:
>> I am seeing similar behavior on Linux as well.  In my case, I carry some
>
> Just wanted to state that the behavior on Linux is similar but not as bad
> as Nick is reporting for OSX.  I get about 20ms worth of extra jitter by
> using the To/FromDevice compared to sending the data via the RawSocket.
>
>> data between two PCs which run user-level click.  If I use RawSocket
>> element, I get much better performance compared to using To/FromDevice
>> and manually composing the frames.
>>
>>
>> On 10:42 am 07/19/10 Nicholas Weaver <nweaver at icsi.berkeley.edu> wrote:
>> > The test configuration:
>> >
>> > FromDevice(en0, PROMISC true) -> CheckIPHeader(14) ->
>> >            IPPrint('reply') -> Discard;
>> >
>> >
>> > A TCPdump running at the same time gets all the packets as they are
>> > received, but the click configuration gets them in bursts (but the
>> > timestamps are right)
>> >
>> > On Jul 19, 2010, at 10:38 AM, Nicholas Weaver wrote:
>> >
>> > > I remember having a similar problem before and I don't remember what
>> > > the solution is...
>> > > On OS-X (latest version, latest devtools), FromDevice is buffering
>> > > up a large number of packets rather than receiving them in real
>> > > time. A TCPdump running at the same time does not have this problem.
>> > >
>> > >
>> > > Suggestions?
>> > >
>> > >
>> > >
>> >
>> >
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>> > https://amsterdam.lcs.mit.edu/mailman/listinfo/click
>>
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