Re: Wrong network usage reported by /proc

[Matthias Saou <thias@spam.spam.spam.spam.spam.spam.spam.egg.and.spam.freshrpms.net>]

Robert Hancock wrote :

> Matthias Saou wrote:
> > Hi,
> > 
> > I'm posting here as a last resort. I've got lots of heavily used RHEL5
> > servers (2.6.18 based) that are reporting all sorts of impossible
> > network usage values through /proc, leading to unrealistic snmp/cacti
> > graphs where the outgoing bandwidth used it higher than the physical
> > interface's maximum speed.
> > 
> > For some details and a test script which compares values from /proc
> > with values from tcpdump :
> > https://bugzilla.redhat.com/show_bug.cgi?id=489541
> > 
> > The values collected using tcpdump always seem realistic and match the
> > values seen on the remote network equipments. So my obvious conclusion
> > (but possibly wrong given my limited knowledge) is that something is
> > wrong in the kernel, since it's the one exposing the /proc interface.
> > 
> > I've reproduced what seems to be the same problem on recent kernels,
> > including the 2.6.27.21-170.2.56.fc10.x86_64 I'm running right now. The
> > simple python script available here allows to see it quite easily :
> > https://www.redhat.com/archives/rhelv5-list/2009-February/msg00166.html
> > 
> >  * I run the script on my Workstation, I have an FTP server enabled
> >  * I download a DVD ISO from a remote workstation : The values match
> >  * I start ping floods from remote workstations : The values reported
> >    by /proc are much higher than the ones reported by tcpdump. I used
> >    "ping -s 500 -f myworkstation" from two remote workstations
> > 
> > If there's anything flawed in my debugging, I'd love to have someone
> > point it out to me. TIA to anyone willing to have a look.
> > 
> > Matthias
> > 
> 
> There may well be a bug in the kernel you're using, but you'd likely 
> have more luck reporting a bug to Red Hat - the RHEL5 kernel is quite 
> old and heavily patched and not many LKML people will likely be familiar 
> with what RH may have done to it..

I've already reported it to Red Hat (through Dell), and have an open
ticket. But I only have basic support, so I have no idea if/when a
problem like this will get escalated to someone with enough knowledge.

But I seem to have been able to reproduce the issue on very recent 2.6
kernels, with different chips/drivers which is why I'm posting here.

Matthias

-- 
Clean custom Red Hat Linux rpm packages : http://freshrpms.net/
Fedora release 10 (Cambridge) - Linux kernel
2.6.27.21-170.2.56.fc10.x86_64 Load : 0.10 0.06 0.01