Red Hat Bugzilla – Bug 160020
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.
*** This bug has been marked as a duplicate of 160019 ***