Comparison of several congestion control algorithms

Comparison of several congestion control algorithms

[Baruch Even]

Hello,

I wanted to point you to a comparison of congestion control algorithm
done at the Hamilton Institute. These experiments compare Scalable-TCP,
High-Speed TCP, FAST-TCP, BIC-TCP, H-TCP and Standard TCP. They compared
  fairness, compatibility with TCP and link utilisation.

You can find the results and a report at http://hamilton.ie/net/eval/

Regards,
Baruch

Re: Comparison of several congestion control algorithms

[David S. Miller]

From: Baruch Even <baruch@ev-en.org>
Date: Sat, 28 May 2005 22:19:01 +0100

> I wanted to point you to a comparison of congestion control algorithm
> done at the Hamilton Institute. These experiments compare Scalable-TCP,
> High-Speed TCP, FAST-TCP, BIC-TCP, H-TCP and Standard TCP. They compared
>   fairness, compatibility with TCP and link utilisation.
> 
> You can find the results and a report at http://hamilton.ie/net/eval/

Nice work, I enjoyed this paper very much.

There is something that none of these papers mention, but is essential
for interpreting results.  Did you use interfaces with TSO enabled?

There is a very serious congestion window growth bug with TSO enabled
in the current 2.6.x tree.  The problem is due to congestion window
validation.  When we build TSO frames, even if we have packets to send,
we may defer a few frames until the full TSO packet can go out.
But this causes the congestion window validation checks in tcp_ack()
to not pass, and thus the congestion window does not grow.

I am going to have this fixed, but for now people should do congestion
window algorithm tests with TSO explicitly disabled on their interfaces.

Re: Comparison of several congestion control algorithms

[Baruch Even]

David S. Miller wrote:
> From: Baruch Even <baruch@ev-en.org>
> Date: Sat, 28 May 2005 22:19:01 +0100
> 
> 
>>I wanted to point you to a comparison of congestion control algorithm
>>done at the Hamilton Institute. These experiments compare Scalable-TCP,
>>High-Speed TCP, FAST-TCP, BIC-TCP, H-TCP and Standard TCP. They compared
>>  fairness, compatibility with TCP and link utilisation.
>>
>>You can find the results and a report at http://hamilton.ie/net/eval/
> 
> 
> Nice work, I enjoyed this paper very much.
> 
> There is something that none of these papers mention, but is essential
> for interpreting results.  Did you use interfaces with TSO enabled?

I did not do these experiments myself, but to the best of my knowledge,
none of the experiments done so far in Hamilton have used the TSO feature.

This is in part because of the start of the work that was based on 2.4
kernels and even as far as the 2.6.6 kernel which had disabled TSO once
it saw SACKs. This made TSO unusable for our needs.

AFAIK, the tests reported in that document used kernel 2.6.6.

Baruch

Re: Comparison of several congestion control algorithms

[David S. Miller]

From: Baruch Even <baruch@ev-en.org>
Date: Fri, 03 Jun 2005 00:50:07 +0100

> This is in part because of the start of the work that was based on 2.4
> kernels and even as far as the 2.6.6 kernel which had disabled TSO once
> it saw SACKs. This made TSO unusable for our needs.
> 
> AFAIK, the tests reported in that document used kernel 2.6.6.

Sure SACKs turn off TSO currently,  but you'll have them enabled
at the beginning until the first loss and this affects how fast
the cwnd will grow.

If you have e1000 cards, for example, you're getting TSO enabled
by default.

You really need to look into this, as it has a real and very
non-trivial effect on all of the results you obtained.

Re: Comparison of several congestion control algorithms

[Baruch Even]

David S. Miller wrote:
> From: Baruch Even <baruch@ev-en.org>
> Date: Fri, 03 Jun 2005 00:50:07 +0100
> 
> 
>>This is in part because of the start of the work that was based on 2.4
>>kernels and even as far as the 2.6.6 kernel which had disabled TSO once
>>it saw SACKs. This made TSO unusable for our needs.
>>
>>AFAIK, the tests reported in that document used kernel 2.6.6.
> 
> 
> Sure SACKs turn off TSO currently,  but you'll have them enabled
> at the beginning until the first loss and this affects how fast
> the cwnd will grow.
> 
> If you have e1000 cards, for example, you're getting TSO enabled
> by default.
> 
> You really need to look into this, as it has a real and very
> non-trivial effect on all of the results you obtained.

I checked that now and ethtool -k shows TSO to be disabled after boot.
Since all the test scripts are not playing with ethtool I can be sure
that TSO was off during all of our tests.

Baruch