G
Graham Marsh
Hi All, the following is some correspondence that I have already forwarded
to Dell, but if anyone is familiar with this issue it would be great to know
about it! Thanks.
Background: We are rolling out our image (of Windows XP SP1a) to the firm
during the summer. We use the sysprep procedure to incorporate support for
multiple hardware platforms. I include the Intel gigabit driver in order to
support the GX270.
The sysprep process works fine, i.e. the driver is correctly installed.
However, the problem is as follows: Users experience very slow send speeds
when, for example, copying files from the local drive to the network drive.
Going the other way is not a problem. The network drive can be a Netware
server, or a Windows server, or another Windows desktop, it doesn't matter
which. We have ruled out duplex issues as a possible cause.
What I have narrowed it down to is a setting called "Offload TCP
Segmentation" which I understand quite well by researching the technology on
the internet. By default, this is switched on. Turning it off appears to
resolve the issue.
This issue seems to be apparent no matter what version of Intel driver is
being used (whether the official one from the Dell gx270 site or the Intel
one from support.intel.com, or a Windowsupdate-sourced driver). A further
problem is that older versions of the driver (including the Dell gx270
official one) do not expose the "Offload TCP Segmentation" setting in the
Driver GUI but it still exists in the registry and is still enabled by
default. I know which setting to change to Disabled (0).
Initially it appeared to be a driver problem which I thought was fixed by
using the older, official Dell version, rather than the most current Intel
version. However, it was not the case, since the problem is intermittent
(during one session the issue may not be apparent; in another session after
a restart, the issue becomes apparent), even with the official driver.
I have done further research and it appears that Linux users also have
performance issues with the 82540EM.
My best guess which may be totally wrong: the traffic going out from the NIC
when TSO is enabled has an MTU that is too high and the infrastructure
causes fragmentation and / or re-sends. Or something like that. I'm not an
infrastructure expert but I know that excessive fragmentation will slow
things down. Perhaps the only way to know what is really going on at the
wire level is to trace it using something like ethereal.
Obviously this is very important to us and it would be a major inconvenience
to have to disable the "Offload TCP Segmentation" setting on the the GX
series with the 82540EM LOM. Additionally, I have simply arrived at this
workaround by a process of elimination, and I would appreciate knowing WHY
this issue is occuring and if there is a proper FIX for it rather than the
workaround I have described, which I am of course still not 100% sure will
really work 100% of the time.
to Dell, but if anyone is familiar with this issue it would be great to know
about it! Thanks.
Background: We are rolling out our image (of Windows XP SP1a) to the firm
during the summer. We use the sysprep procedure to incorporate support for
multiple hardware platforms. I include the Intel gigabit driver in order to
support the GX270.
The sysprep process works fine, i.e. the driver is correctly installed.
However, the problem is as follows: Users experience very slow send speeds
when, for example, copying files from the local drive to the network drive.
Going the other way is not a problem. The network drive can be a Netware
server, or a Windows server, or another Windows desktop, it doesn't matter
which. We have ruled out duplex issues as a possible cause.
What I have narrowed it down to is a setting called "Offload TCP
Segmentation" which I understand quite well by researching the technology on
the internet. By default, this is switched on. Turning it off appears to
resolve the issue.
This issue seems to be apparent no matter what version of Intel driver is
being used (whether the official one from the Dell gx270 site or the Intel
one from support.intel.com, or a Windowsupdate-sourced driver). A further
problem is that older versions of the driver (including the Dell gx270
official one) do not expose the "Offload TCP Segmentation" setting in the
Driver GUI but it still exists in the registry and is still enabled by
default. I know which setting to change to Disabled (0).
Initially it appeared to be a driver problem which I thought was fixed by
using the older, official Dell version, rather than the most current Intel
version. However, it was not the case, since the problem is intermittent
(during one session the issue may not be apparent; in another session after
a restart, the issue becomes apparent), even with the official driver.
I have done further research and it appears that Linux users also have
performance issues with the 82540EM.
My best guess which may be totally wrong: the traffic going out from the NIC
when TSO is enabled has an MTU that is too high and the infrastructure
causes fragmentation and / or re-sends. Or something like that. I'm not an
infrastructure expert but I know that excessive fragmentation will slow
things down. Perhaps the only way to know what is really going on at the
wire level is to trace it using something like ethereal.
Obviously this is very important to us and it would be a major inconvenience
to have to disable the "Offload TCP Segmentation" setting on the the GX
series with the 82540EM LOM. Additionally, I have simply arrived at this
workaround by a process of elimination, and I would appreciate knowing WHY
this issue is occuring and if there is a proper FIX for it rather than the
workaround I have described, which I am of course still not 100% sure will
really work 100% of the time.