SACK performance improvements - technical report and updated 2.6.6 patches

SACK performance improvements - technical report and updated 2.6.6 patches

[Baruch Even]

Hello,

I wanted to post an update about my work for SACK performance
improvements, I've updated the patches on our website and added a
technical report on the work so far.

It can be found at:
http://hamilton.ie/net/research.htm#patches

In summary: The Linux stack so far is unable to effectively handle
single transfers on 1Gbps with high rtt links (220 ms rtt is what we
tested). The sender is unable to process the ACK packets fast enough
causing lost  ACKs and increased transfer times. Our work resulted in a
set of patches that enable the Linux TCP stack to handle this load
without breaking sweat.

Your comments on this work would be appreciated.

Regards,
Baruch

Re: SACK performance improvements - technical report and updated 2.6.6 patches

[Craig Partridge]

Thanks for sharing!

I found the report fun reading in the sense that I don't know of many folks
who've worked on slow path performance improvement.

However, having written some of these kinds of papers in the past, I'll point
out that before it could be considered publishable, it needs a much clearer
explanation of the algorithms in the actual code and precisely how they
were modified.  For instance, it wasn't clear to me if the SACK block
code walked the list of outstanding segments for each SACK block or walked
the list of segments once, checking all the SACK blocks (they are both
n*s algorithms, but the second algorithm will have decidedly better
performance due to locality and ordering tricks you can play).

Also, it was not clear why the revised algorithm grows as O(lost packets)
vs O(cwnd).

Thanks!

Craig

In message <43A7178E.4030808@ev-en.org>, Baruch Even writes:

>Hello,
>
>I wanted to post an update about my work for SACK performance
>improvements, I've updated the patches on our website and added a
>technical report on the work so far.
>
>It can be found at:
>http://hamilton.ie/net/research.htm#patches
>
>In summary: The Linux stack so far is unable to effectively handle
>single transfers on 1Gbps with high rtt links (220 ms rtt is what we
>tested). The sender is unable to process the ACK packets fast enough
>causing lost  ACKs and increased transfer times. Our work resulted in a
>set of patches that enable the Linux TCP stack to handle this load
>without breaking sweat.
>
>Your comments on this work would be appreciated.
>
>Regards,
>Baruch

Re: SACK performance improvements - technical report and updated 2.6.6 patches

[Injong Rhee]

I wonder the same. I wonder how this new patch by the HTCP folks
improves what we provided for the 2.6.x (which is currently
incorporated in the latest linux version). My recollection says that
this HTCP patch periodically crashes the system very often -- so we
could not run the comparison. BTW, this fast SACK path fix we provided
are just a simple clean-up and modification from the original Tom
Kelly's SACK code - so Tom deserves the full credit for it.


> -----Original Message-----
> From: netdev-owner@vger.kernel.org [mailto:netdev-
> owner@vger.kernel.org] On Behalf Of David S. Miller
> Sent: Monday, December 19, 2005 4:23 PM
> To: baruch@ev-en.org
> Cc: netdev@vger.kernel.org; end2end-interest@postel.org;
> d.leith@eee.strath.ac.uk
> Subject: Re: SACK performance improvements - technical report and
> updated 2.6.6 patches
> 
> From: Baruch Even <baruch@ev-en.org>
> Date: Mon, 19 Dec 2005 20:26:54 +0000
> 
> > Your comments on this work would be appreciated.
> 
> Ummm... how about the patches that fix this which are in the 2.6.x
> kernel already?
> 
> Yes, it's not your stuff, but it was incredibly less invasive and
> probably works nearly as well.
> -
> To unsubscribe from this list: send the line "unsubscribe netdev" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

Re: SACK performance improvements - technical report and updated 2.6.6 patches

[Injong Rhee]

Ditto. I remember we had some discussion on this sometime back in the
netdev mailing list (Baruch was part of the discussion).

> -----Original Message-----
> From: David S. Miller [mailto:davem@davemloft.net]
> Sent: Tuesday, December 20, 2005 4:09 AM
> To: doug@eee.strath.ac.uk
> Cc: rhee@eos.ncsu.edu; baruch@ev-en.org; netdev@vger.kernel.org;
> end2end-interest@postel.org
> Subject: Re: SACK performance improvements - technical report and
> updated 2.6.6 patches
> 
> From: "Douglas Leith" <doug@eee.strath.ac.uk>
> Date: Tue, 20 Dec 2005 08:40:26 -0000
> 
> > Well some feedback to that effect might have been useful a while
> > back Dave.
> 
> I gave him feedback on at least 5 seperate occaisions, both
> publicly and in private correspondance.
> 
> Others have done so as well.