tcp_window_scaling degrades performance

tcp_window_scaling degrades performance

[Maciej Soltysiak]

Hi

I have been experiencied weird problems with network throughput
lately and I after experimenting with /proc/sys/net/ipv4 knobs
I found that when I have tcp_window_scaling 0 I can
get throughput from a distant server of about 600kB/s (well, 200kB/s
is fast enough)

   # links ftp://ftp.task.gda.pl/ls-lR

When I turn tcp_window_scaling to 1 the transfer starts with 600kB,
then drops nicely to 20kB/s then starts growing again and reaches
about 400kB/s

Anyway It works, but there are some hosts, with which I can't talk to
faster than 800B/s !

This is a Debian SID with vanilla-2.6.7-bk20, but I am having these
problems for a few weeks now.

It might be a TCP kernel issue, but I know that between me and the
other hosts is a checkpoint fw-1 fp3, it may be the cause of problems,
because, well, checkpoint is crazy.

Anyway, I can provide tcpdump, and tcptrace analysis of it and the
state of sysctls if anyone would be willing to help me figure out
what's going on.

Regards,
Maciej

Re: tcp_window_scaling degrades performance

[Kasper Sandberg]

hey, are you having some kind of hardware router?
bert hubert, helped me, and we found out my router was causing me the
problems, however, my problems were more severe, as my limit was 50kb/s

On Thu, 2004-07-15 at 17:09 +0200, Maciej Soltysiak wrote:
> Hi
> 
> I have been experiencied weird problems with network throughput
> lately and I after experimenting with /proc/sys/net/ipv4 knobs
> I found that when I have tcp_window_scaling 0 I can
> get throughput from a distant server of about 600kB/s (well, 200kB/s
> is fast enough)
> 
>    # links ftp://ftp.task.gda.pl/ls-lR
> 
> When I turn tcp_window_scaling to 1 the transfer starts with 600kB,
> then drops nicely to 20kB/s then starts growing again and reaches
> about 400kB/s
> 
> Anyway It works, but there are some hosts, with which I can't talk to
> faster than 800B/s !
> 
> This is a Debian SID with vanilla-2.6.7-bk20, but I am having these
> problems for a few weeks now.
> 
> It might be a TCP kernel issue, but I know that between me and the
> other hosts is a checkpoint fw-1 fp3, it may be the cause of problems,
> because, well, checkpoint is crazy.
> 
> Anyway, I can provide tcpdump, and tcptrace analysis of it and the
> state of sysctls if anyone would be willing to help me figure out
> what's going on.
> 
> Regards,
> Maciej
> 
> 
> -
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at  http://www.tux.org/lkml/
> 

Re[2]: tcp_window_scaling degrades performance

[Maciej Soltysiak]

KS> hey, are you having some kind of hardware router?
Well, there is a hardware router, 3com but it's a local router,
the router that sends the traffic to the Internet link is a checkpoint
firewall-1 on running on linux.

I have 2 linux-2.6 machines, this weird behaviour is only with them.

Regards,
Maciej

Re: Re[2]: tcp_window_scaling degrades performance

[Kasper Sandberg]

On Thu, 2004-07-15 at 17:25 +0200, Maciej Soltysiak wrote:
> KS> hey, are you having some kind of hardware router?
> Well, there is a hardware router, 3com but it's a local router,
> the router that sends the traffic to the Internet link is a checkpoint
> firewall-1 on running on linux.
> 
> I have 2 linux-2.6 machines, this weird behaviour is only with them.
yes, but its not linux that behaves wrong, if you actually do have a
hardware router, its probably the router doing wrong. changing to linux
router and it works :)
> 
> Regards,
> Maciej
> 
> 
> -
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at  http://www.tux.org/lkml/
> 

Re: tcp_window_scaling degrades performance

[Andi Kleen]

Maciej Soltysiak <solt@dns.toxicfilms.tv> writes:


> I have been experiencied weird problems with network throughput
> lately and I after experimenting with /proc/sys/net/ipv4 knobs
> I found that when I have tcp_window_scaling 0 I can
> get throughput from a distant server of about 600kB/s (well, 200kB/s
> is fast enough)

It's pretty easy for you to find out. Do a tcpdump -v or ethereal -v 
from both the side of a host you download from and from the linux side.
Then compare all packets. If they don't match the firewall is 
doing something bad. Especially check window values and TCP options
in the SYN packets

It is very very likely the firewall, window scaling works for a lot
of people.

-Andi