Ping RTT clock resolution problem on x86_64

[Joshua Jensen]

Please say that you have entered this in bugzilla... this is important

Joshua



On Thu, Oct 14, 2004 at 01:58:57PM -0700, Federico Sacerdoti wrote:
> Hello,
> 
> I am a developer from the Rocks project in San Diego. We are noticing a 
> problem with the clock resolution for TCP round trip times that only 
> emerges on AMD Opteron systems. The bug is characterized as follows:
> 
> The issue is that the clock resolution is only 10ms: ie any rtt value 
> between 0-10ms is reported as 0.00ms.
> 
> --On Opteron (bug)--
> root at www root]# ping google.com
> PING google.com (216.239.37.99) 56(84) bytes of data.
> 64 bytes from 216.239.37.99: icmp_seq=0 ttl=238 time=89.9 ms
> 64 bytes from 216.239.37.99: icmp_seq=1 ttl=238 time=79.9 ms
> 64 bytes from 216.239.37.99: icmp_seq=2 ttl=236 time=79.9 ms
> 
> [root at www root]# ping nbc.com
> PING nbc.com (63.241.60.70) 56(84) bytes of data.
> 64 bytes from nbc.com (63.241.60.70): icmp_seq=0 ttl=53 time=0.000 ms
> 64 bytes from nbc.com (63.241.60.70): icmp_seq=1 ttl=53 time=0.000 ms
> 
> 
> --On Other systems (normal)--
> [root at rocks-43 root]# ping google.com
> PING google.com (216.239.57.99) 56(84) bytes of data.
> 64 bytes from 216.239.57.99: icmp_seq=0 ttl=244 time=11.5 ms
> 64 bytes from 216.239.57.99: icmp_seq=1 ttl=244 time=11.8 ms
> 64 bytes from 216.239.57.99: icmp_seq=2 ttl=244 time=11.5 ms
> 64 bytes from 216.239.57.99: icmp_seq=3 ttl=244 time=11.7 ms
> 
> [root at rocks-43 root]# ping nbc.com
> PING nbc.com (63.241.60.70) 56(84) bytes of data.
> 64 bytes from nbc.com (63.241.60.70): icmp_seq=0 ttl=53 time=7.41 ms
> 64 bytes from nbc.com (63.241.60.70): icmp_seq=1 ttl=53 time=7.32 ms
> 64 bytes from nbc.com (63.241.60.70): icmp_seq=2 ttl=53 time=7.39 ms
> 64 bytes from nbc.com (63.241.60.70): icmp_seq=3 ttl=53 time=7.33 ms
> 
> 
> This behavior happens for several different types of ethernet cards on 
> opterons, and is not observed on either Pentium or Nocona systems.
> 
> Has anyone noticed this before? Our kernel version is:
> 
> (Nocona)
> Linux rocks-43.sdsc.edu 2.4.21-20.EL #1 SMP Fri Oct 1 09:12:23 PDT 2004 
> x86_64 x86_64 x86_64 GNU/Linux
> 
> (Opteron)
> Linux www.rocksclusters.org 2.4.21-20.ELsmp #1 SMP Sat Sep 18 18:28:16 
> PDT 2004 x86_64 x86_64 x86_64 GNU/Linux
> 
> Thank you,
> Federico
> 
> Rocks Cluster Group, San Diego Supercomputer Center, CA
> 
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-- 
Joshua Jensen
joshua at iwsp.com
"If God didn't want us to eat animals, why did he make them out of meat?"