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Multiport network adapter vs separate network adapters, diff

by adoado0 / April 1, 2013 8:24 PM PDT

Hello all,
I am looking for some information concerning network adapters. Many server vendors (HP, Dell, IBM and so on) use multiport single network adapter (one card,several ports -let's assume 4 ports).

Does anybody have some link or information about differences between such solution (4port card) vs separate one (or dual) port cards? What resources are shared in multiport solution? For example:
- does multiport nic has significant limitations? For example, it's cpu cannot handle full 4-port load?
- interrupt sharing?
- buffer size?

If it is crucial - I am interested in HP/Dell server as router and need to have some info about performance of multiport adapter.
Hope somebody can give some clues.

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All Answers

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I'll share a bit from the past.
by R. Proffitt Forum moderator / April 2, 2013 1:23 AM PDT

Gene Amdahl, mused about the relationship between I/O and CPU so you can find his writings to learn what he proposed. In short unless you have a very low end CPU there is little difference from one card to the next. Most of the overhead I see is somewhere else such as the SQL engine and poor code I've seen there.

The only time I've looked at the interrupt and such was in our embedded designs where we use a few hundred MHz CPU. And since PCI and PCIe interrupts are not shared, there is no issue there again.

Here's a clue. If you have a single core CPU, I could see why you would worry.

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I am afraid we misunderstood
by adoado0 / April 3, 2013 11:05 PM PDT

Cpu is Sandy Bridge Six Core. To sum up I mean NIC limitations not whole server. What resources are shared between ports in multiport NIC? Let's assume that One-port NIC has one processing unit and 4-port nic can share one processing unit or can have 4 independent processing units. So it is my question. What are performance drawbacks of multiport NICs comparing to separate one-port NICs.

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Should be hard to measure.
by R. Proffitt Forum moderator / April 4, 2013 2:04 AM PDT

Again, given there are no shared interrupts in PCI or PCIe that's not a performance issue.

Also, let's for discussion sake say that 4 NICs are on one card. As each buffer fills and a request is made on possibly one IRQ then what's the overhead?

I see the usual IRQ fire up and it has to read one byte from the card to determine which nic needs service. Then a call to that service routine.

So for the usual system, at most a 1 uS overhead per packet and more likely in the nanoseconds as the content will have already been DMA'd into the right spot in memory ready for the driver.

You have a good question but are going to be upset that you can't find any big payback here. You would get more out of better SQL code.

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