netdev - Re: under-performing bonded interfaces

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Date:	Wed, 16 Nov 2011 20:45:15 -0500
From:	Simon Chen <simonchennj@...il.com>
To:	Ben Hutchings <bhutchings@...arflare.com>
Cc:	Ben Greear <greearb@...delatech.com>, netdev@...r.kernel.org
Subject: Re: under-performing bonded interfaces

Emm, actually two different PCIe slots. But one slot is only
5.0Gbps... Seem pretty clear from the message below, wasn't reading
thoroughly :-(

[   11.572857] ixgbe 0000:03:00.0: Multiqueue Enabled: Rx Queue count
= 24, Tx Queue count = 24
[   11.572861] ixgbe 0000:03:00.0: (PCI Express:5.0Gb/s:Width x4)
e8:9a:8f:23:42:1a
[   11.572943] ixgbe 0000:03:00.0: MAC: 2, PHY: 8, SFP+: 3, PBA No: FFFFFF-0FF
[   11.572944] ixgbe 0000:03:00.0: PCI-Express bandwidth available for
this card is not sufficient for optimal performance.
[   11.572946] ixgbe 0000:03:00.0: For optimal performance a x8
PCI-Express slot is required.
[   11.573815] ixgbe 0000:03:00.0: Intel(R) 10 Gigabit Network Connection
[   11.573833] ixgbe 0000:03:00.1: PCI INT B -> GSI 34 (level, low) -> IRQ 34
[   11.573839] ixgbe 0000:03:00.1: setting latency timer to 64



On Wed, Nov 16, 2011 at 8:38 PM, Simon Chen <simonchennj@...il.com> wrote:
> Thanks, Ben. That's good discovery...
>
> Are you saying that both 10G NICs are on the same PCIe x4 slot, so
> that they're subject to the 12G throughput bottleneck?
>
> I'm gonna verify this with the hardware vendor...
>
> Thanks.
> -Simon
>
> On Wed, Nov 16, 2011 at 7:57 PM, Ben Hutchings
> <bhutchings@...arflare.com> wrote:
>> On Wed, 2011-11-16 at 19:05 -0500, Simon Chen wrote:
>>> If used independently, I can get around 9.8Gbps.
>> [...]
>>> [   11.572861] ixgbe 0000:03:00.0: (PCI Express:5.0Gb/s:Width x4) e8:9a:8f:23:42:1a
>> [...]
>>
>> You need a PCIe 2.0 x8 slot to run 2 10 Gb ports at full speed.  An x4
>> slot is only good for about 12-13 Gb aggregate throughput (dependent on
>> packet sizes and other details).
>>
>> Ben.
>>
>> --
>> Ben Hutchings, Staff Engineer, Solarflare
>> Not speaking for my employer; that's the marketing department's job.
>> They asked us to note that Solarflare product names are trademarked.
>>
>>
>
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