Advice on a multithreaded netisr patch?

Sepherosa Ziehau sepherosa at
Mon Apr 6 22:21:37 PDT 2009

On Sun, Apr 5, 2009 at 9:34 PM, Ivan Voras <ivoras at> wrote:
> Robert Watson wrote:
>> On Sun, 5 Apr 2009, Ivan Voras wrote:
>>> I thought this has something to deal with NIC moderation (em) but
>>> can't really explain it. The bad performance part (not the jump) is
>>> also visible over the loopback interface.
>> FYI, if you want high performance, you really want a card supporting
>> multiple input queues -- igb, cxgb, mxge, etc.  if_em-only cards are

PCI-E em(4) supports 2 RX queues.  82571/82572 support 2 TX queues.
I have not tested multi-TX queues, but em(4) multi-RX queues work well
in dfly (tested with 82573 and 82571)

>> fundamentally less scalable in an SMP environment because they require
>> input or output to occur only from one CPU at a time.
> Makes sense, but on the other hand - I see people are routing at least
> 250,000 packets per seconds per direction with these cards, so they
> probably aren't the bottleneck (pro/1000 pt on pci-e).

It should be some variants of 82571EB

Best Regards,

Live Free or Die

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