Re: XTP for 2.6.25

From: Shigeo N
Date: Fri Apr 25 2008 - 04:00:00 EST


I emulated WAN delay by netem and compared the performance again.

case1) fixed delay

<------------- 100Mbps -------------->
Host1 --------- Linux Router ---------- Host2

In this case, just adds a fixed amount of delay to all packets going
out on Linux Router by command, "tc qdisc add dev eth0 root netem
delay 100ms".

Here is the result.

fixed delay UDP/TCP/XTP throghput
---------------------------------------
10ms 88/85/92 Mbps
30ms 88/70/91 Mbps
50ms 88/63/89 Mbps
70ms 88/52/84 Mbps
100ms 88/36/70 Mbps


case2) random delay

In this case, add a fixed amount of delay + 10% random delay by
command, "tc change dev eth0 root netem delay 100ms 10ms 25%".

Here is the result.

fixed delay UDP/TCP/XTP throghput
---------------------------------------
10ms 88/80/92 Mbps
30ms 88/51/91 Mbps
50ms 88/41/89 Mbps
70ms 88/28/80 Mbps
100ms 88/19/66 Mbps

TCP's perfomance looks very poor when delay is long and variable.

Thanks
Shigeo


On Thu, Apr 24, 2008 at 10:06 PM, Shigeo N <shigeonx@xxxxxxxxx> wrote:
> Now I have connected 2 hosts directly, and evaluate the each throughput.
> Then all the results of UDP, TCP and XTP are the same and 94Mbps. (My
> netwrok is 100Base/TX).
>
> In this case round-trip time between 2 hosts is less than 0.1ms
> because they are directly connected. But my previouse case, round-trip
> time between 2 hosts are 4ms. (I use IPSEC between the security
> gateways to increase delay).
> I think that's the reason TCP throughput is slow. If ACK packets are
> delayed, sending window cannot slide and sending packets cannot be
> fully bursted.
>
> If I changes wmem size through /proc/sys/net/ipv4/tcp_wmem, TCP's
> throughput may improve, but congestion control becomes more difficult
> for TCP.
>
> That is TCP's disadvantage to XTP.
>
> Best
> Shigeo
>
>
>
> On 4/24/08, Andi Kleen <andi@xxxxxxxxxxxxxx> wrote:
> > "Shigeo N" <shigeonx@xxxxxxxxx> writes:
> > >
> > > I tested in the network where UDP throughput is 29Mbps, then TCP
> > > throughput was 13Mbps, but XTP's reached to 25Mbps.
> >
> > One interesting question is why TCP was so much slower than UDP
> > on your test. It shouldn't be on a fair test setup.
> >
> > Please post details. Was the network losing packets?
> >
> > New protocols might be interesting, but even more interesting is to
> > fix any (real) problems in existing protocols.
> >
> > -Andi
> >
>
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