Red Hat Bugzilla – Bug 160019
Full-duplex Gigabit can not reach gigabit at both RX/TX same time
Last modified: 2007-11-30 17:07:07 EST
Description of problem:
Full-duplex mode Gigabit can not reach near gigabit at both sending and
receiving sides. Instead, the sum of sending and receiving reaches gigabit.
The tests are ttcp tests on two HP workstation XW4200.
Case 1, only receiving, no sending.
The sending speed is near 0MBytes/s, receiving speed is 110MB/s.
case 2, only sending, no receiving.
The sending speed is near 110MB/s, receiving speed is near 0MB/s.
case 3, both sending and receiving at the same time.
The sending speed is about 55MB/s, receiving at about 55MB/s.
Version-Release number of selected component (if applicable):
Not only on Redhat Enterprise Linux, but also on Fedora Core series.
Steps to Reproduce:
1. Install Redhat Enterprise 3 or 4 onto two HP Workstation XW4200, or similar
machines with high PCI Bus speed. and connect the builtin Broadcom network
cards with a crossover CAT6 cable. This way exclues the LAN Switch factor.
2. run ttcp on the two machines, either as sending role, or as receiving role.
3.test all the 3 cases in the "Description of Problem" section. and the
results will be quite similar.
When machines' gigabit(in full-duplex gigabit mode) in sending and receiving
data at the same time, both the sending speed and receiving speed should be
around 110MB/s. And the SUM of them should be 220MB/s.
According to HP support technician, the HP workstation XW4200 has a PCI
EXpress bus which support 2.5GB/s data transfer. "top" commands reports that
machine box still have 80% Idle CPU cycles.
*** Bug 160020 has been marked as a duplicate of this bug. ***
Not true, the some should not be 220MB/sec. You're forgetting
that the opposite direction of the transfer is consumed by ACK
So for the single transfer case you have:
SENDER --> DATA --> DATA --> DATA --> DATA --> DATA --> RECEIVER
SENDER <-- ACK <-- ACK <-- ACK <-- ACK <-- ACK <-- RECEIVER
With the case of two transfers going at once you have:
Host1 --> DATA --> ACK --> DATA --> ACK --> DATA --> ACK Host2
Host2 <-- ACK <-- DATA <-- ACK <-- DATA <-- ACK <-- DATA Host2
This is not a bug.
David Miller, Thanks for you quick reply.
But I've also tested the normal 100Mbits/s network cards in full-duplex modes.
with two pairs of sending-receiving ttcp on two Redhat Linux hosts.
The results are: On each machine, the sending side speed is 12MB/s, receiving
speed is also at 12MB/s. totally the SUM is 24MB/s, quite close to the
capacity of 200Mbits/s(added sending and receiving sides).
The above is quite easy to reproduce, you can use two 100Mbits/s cards, or
Gigabit works at 100Mbits/s fFull-duplex mode. The OS can be Redhat Enterprise
Linux or Fedora Core, kernel can be 2.4 or 2.6. The results is exactly the
What NICs are you using (particular in the xw4200)? Are they actually PCI-E?
Or are they PCI(-X)?
Please attach the output of running "sysreport" to this bug. Thanks!
Closed due to inactivity. Please reopen when requested information becomes