On Thu, Feb 26, 2015 at 9:18 AM, Laurent Wandrebeck <
l.wandrebeck@xxxxxxxxxxxxxxx> wrote:
> Hi there,
>
> I’m working on deploying our new cluster.
> Masters have 5×1gbps (i210 and i350, thus using igb.ko), configured with
> mtu 9000, 802.3ad. Works fine *but* I can’t get DCB working (pause frame,
> aka flow control, which is supported by and enabled on our switches).
>
> [root@master2 ~]# dcbtool gc eno1 dcb
> Command: Get Config
> Feature: DCB State
> Port: eno1
> Status: Device not capable
>
> (I get the same with ELRepo 5.2.15 kmod).
> Intel datasheet says flow control is available.
> Can’t find much about it on the web or in kernel git repo. Could someone
> give me a hand ?
>
> Regards,
> Laurent.
>
DCB requires Priority Flow Control(PFC) aka 802.1Qbb.
"Flow Control" is 802.3x.
The two are often confused and not compatible.
http://www.intel.com/content/www/us/en/ethernet-controllers/ethernet-controller-i350-datasheet.html
Mentions "flow control" several times, but never
PFC/priority-flow-control/802.1Qbb.
PFC capable switches purposefully disable 802.3x flow control. Also PFC has
to negotiate between two devices/switches matching QoS/CoS/no-drop policies.
Some good reading for beginner PFC knowledge:
http://www.cisco.com/c/dam/en/us/solutions/collateral/data-center-virtualization/ieee-802-1-data-center-bridging/at_a_glance_c45-460907.pdf
What exactly are you trying to pause? Typically FCoE/iSCSI is set to
"no-drop" and Ethernet traffic is paused/dropped in favor of storage
traffic. If there is only one type/class/CoS of traffic PFC won't gain much
over regular flow control/802.3x.
Hope that helps.
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