[SOLVED] Re: Gigabit ethernet low traffic and high latency

[Sylvain Le Gall <gildor@debian.org>]

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On 15-05-2007, Sylvain Le Gall <gildor@debian.org> wrote:
> Hello,
>
> I have spend the two last day, trying to solve a strange problem. I have
> 2 hosts connected using Gigabit Ethernet link and a switch between:
> * host giga: NFS server, Cat6 SFTP link, RTL8111/8168B NIC (r8169), Core 2 Duo
>   T7600, 1GB RAM, SATA drive (xen dom0), linux 2.6.18, etch
> * host grand: NFS client, Cat6 SFTP link, 3C940 NIC (skge), P4 SMT, 1GB
>   RAM, linux 2.6.21.1, sid
> * switch 3Com OfficeConnect 8 port Gigabit, all links negotiate
>   1000BaseT/full
>
> The directory /home/share/backup/old/gildor/ contains a lot of hidden
> files (former home dir).
>
> Here is my test :
> grand$> umount /home/share && mount /home/share
> grand$> time ls /home/share/backup/old/gildor/
> ...
> real    0m59.553s
> user    0m0.000s
> sys     0m0.000s
>
>
> giga$>ping -i 0.2 grand
>
> grand$> umount /home/share && mount /home/share
> grand$> time ls /home/share/backup/old/gildor/
> ...
>
> real    0m0.470s
> user    0m0.000s
> sys     0m0.000s
>
> When a ping is running hitting the host, the NFS returns almost
> immediatly. It is possible to run the ping on both host, but you need to
> ping the other end. This has no effect when you ping broadcast, or
> another non existing host.
>
> I try to :
> * change the switch
> * use other host as NFS client
> * follow indication of http://dsd.lbl.gov/TCP-tuning/linux.html and
>   http://datatag.web.cern.ch/datatag/howto/tcp.html
> * change cable
> * connect directly one host to another
> * add hosts to /etc/hosts 
> * disable/enable host caching in nscd
>
> Does anyone already solve this problem ?
>
> Regards,
> Sylvain Le Gall
>
>

OK, i have worked and solved this problem... This was a driver problem.
Taking a look at the SCM of Linux kernel, i see that there was a lot of
patch on r8169 since the 2.6.18-4 release. Since, i don't want to change
my kernel for now, i decided to use realtek r1000 module... It changes
my life:

grand:~$ umount /home/share && mount /home/share
grand:~$ time ls /home/share/backup/old/gildor

real    0m0.006s
user    0m0.000s
sys     0m0.000s

This is **amazing**! I mean it is really fast.

I think that r8169 in 2.6.21.1 should have the same speed. I just need
to take time to build a kernel (and replace realtek driver by linux
driver).

Regards,
Sylvain Le Gall

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