Hello,
I indend to do some experiments with 802.3x pause frames, but I have yet
to find a setup that works. I used a tool that generates pause frames
[1] in two setups. First one consists of two virtual machines on a
VMWare ESXi 5.5 server connected with each other through a virtual
switch. In second setup two physical machines (Desktop PCs) were
connected directly by an ethernet cable. The VMs are running Debian
Wheezy 32bit while Debian Testing (Jessie) 64bit is installed on both
desktop PCs. Below you will find some information on the ethernet
adapters and drivers used in the VM [2], the desktop PC with the more up
to date hardware [3] and the older machine [4]. I used the following
command to activate flow control:
ethtool -A autoneg off rx on tx on
First of all I noticed some discrepancies between the output of
mii-tools or ethtool -a and the attempt to change the flow control
settings with the command above. Only the Realtek adapter actually
output that it didn't support the operation, the other adapters accepted
the settings without any error message.
In both setups pause frames were generated on one machine while a ping
was sent simultaneously, as suggested in [1]. While the VM connection
was set to 1 Gbps the whole time, I also tested a 10 Mbps setting on the
physical connection. Even though the pause frames were always visible in
tcpdump at the receiver, I didn't notice any influence whatsoever in the
ping results.
Did I miss some important settings that activate pause frame support, or
is it possible that none of those different ethernet adapters and
modules that were tested support at least the reception of pause frames?
If so, are there any adapters that do support them? I'm also not sure
how to interpret the output of ethtool. E.g. what does "Advertised pause
frame use" mean, exactly?
Many thanks.
Julia Niewiejska
[1] http://www.tux.org/pub/sites/www.zip.com.au/%257Eakpm/linux/#flow-ctrl
--
[2] Virtual machine on VMWare ESXi 5.5: Debian Wheezy 32bit, kernel 3.2
*** lspci -v ***
02:02.0 Ethernet controller: Intel Corporation 82545EM Gigabit Ethernet
Controller (Copper) (rev 01)
Subsystem: VMware PRO/1000 MT Single Port Adapter
Physical Slot: 34
Flags: bus master, 66MHz, medium devsel, latency 0, IRQ 16
Memory at fd5a (64-bit, non-prefetchable) [size=128K]
Memory at fdfe (64-bit, non-prefetchable) [size=64K]
I/O ports at 2040 [size=64]
[virtual] Expansion ROM at ebb1 [disabled] [size=64K]
Capabilities: [dc] Power Management version 2
Capabilities: [e4] PCI-X non-bridge device
Kernel driver in use: e1000
*** mii-tool -v ***
eth1: negotiated 1000baseT-FD flow-control, link ok
product info: Yukon 88E1011 rev 3
basic mode: autonegotiation enabled
basic status: autonegotiation complete, link ok
capabilities: 1000baseT-FD 100baseTx-FD 100baseTx-HD 10baseT-FD
10baseT-HD
advertising: 1000baseT-HD 1000baseT-FD 100baseTx-FD 100baseTx-HD
10baseT-FD 10baseT-HD
link partner: 1000baseT-FD 100baseTx-FD 100baseTx-HD 10baseT-FD
10baseT-HD
*** ethtool eth1 ***
Settings for eth1:
Supported ports: [ TP ]
Supported link modes: 10baseT/Half 10baseT/Full
100baseT/Half 100baseT/Full
1000baseT/Full
Supported pause frame use: No
Supports auto-negotiation: Yes
Advertised link modes: 10baseT/Half 10baseT/Full
100baseT/Half 100baseT/Full
1000baseT/Full
Advertised pause frame use: No
Advertised auto-negotiation: Yes
Speed: 1000Mb/s
Duplex: Full
Port: Twisted Pair
PHYAD: 0
Transceiver: internal
Auto-negotiation: on
MDI-X: Unknown
Supports Wake-on: d
Wake-on: d
Current message level: 0x0007 (7)
drv probe link
Link detected: yes
*** ethtool -a eth1 ***
Pause parameters for eth1:
Autonegotiate: on
RX: off
TX: off
--
[3] Desktop PC 1: Debian Jessie 64bit, kernel 3.16
*** lspci -v ***
03:00.0 Ethernet controller: Realtek Semiconductor Co., Ltd.
RTL8111/8168/8411 PCI Express Gigabit Ethernet Controller (rev 0c)
Subsystem: ASUSTeK Computer Inc. Device 8554
Flags: bus master, fast devsel, latency 0, IRQ 44
I/O ports at d000 [size=256]
Memory at f710 (64-bit, non-prefetchable) [size=4K]
Memory at f210 (64-bit, prefetchable) [size=16K]
Capabilities: [40] Power Management version 3
Capabilities: [50] MSI: Enable+ Count=1/1 Maskable- 64bit+
Capabilities: [70] Express Endpoint, MSI 01
Capabilities: [b0] MSI-X: Enable- Count=4 Masked-
Capabil
