Hacker News Reader

Comment by ra1n85 | Hacker News Reader

16 iperf threads...sending at what packet size? Do you understand the notion of line rate? 85Gbps at 1500B is only 7MPPS, which is half of 10Gbps at line rate.

View on HN

Where are you getting your definitions? I have never seen "line rate" used to refer to packets per second.

It implies it. Ethernet at 84B per frame is the smallest you can go, thus the line rate - some examples:

https://events19.linuxfoundation.org/wp-content/uploads/2017...

https://www.redhat.com/en/blog/pushing-limits-kernel-network...

https://kernel-recipes.org/en/2014/ndiv-a-low-overhead-netwo...

"How do you fill a 100GBps pipe with small packets?"

"achieve 10 Gbps line rate at 60B frames"

"reaching line rate on all packet sizes"

Line rate is just bits per second. You have to add in a qualifier about packet size before you're talking about packets per second.

Nope, I'm sorry you're not quite getting it here. Minimum Ethernet frame is 84B on the wire - it's simple enough from there.

I've never heard this weird qualification for the definition of "line rate" that it somehow requires minimum packet size, so I looked it up. The first three sources for a quoted big-g search all imply or directly state that it's the same as bandwidth:

https://blog.ipspace.net/2009/03/line-rate-and-bit-rate.html

https://www.reddit.com/r/networking/comments/4tk2to/bandwidt...

https://www.fmad.io/blog-what-is-10g-line-rate.html

Also, for gigabit networks, ethernet packets are padded to at least 512 bytes because of a bigger slot size: https://www.cse.wustl.edu/~jain/cis788-97/ftp/gigabit_ethern...

Line rate doesn't imply small packets. But most userspace benchmarking uses 64B packets. That being said, the "imix" packet size, which is supposed to represent internet traffic, is around 500B.

There are numerous imix definitions floating around now, it really depends on who you ask. The more realistic ones define a pattern of different sized packets. And performance varies greatly depending on which imix flavour you use, which probably goes back to the earlier poster's 'dumpster fire' comment (although I don't know exactly what NPU generation they are referring to).

Line rate does imply pps at the smallest sized frames in the context of networking equipment performance. Vendors use it extensively in their docs.

64B is the minimum frame size in Ethernet, including interframe gap and preamble its 84B on the wire. It is the same with Ethernet, Gigabit Ethernet and even 100Gbit Ethernet, that source is not correct.

https://kb.juniper.net/InfoCenter/index?page=content&id=KB14...

No line rate does not "imply pps at the smallest sized frames."

Network hardware always quote PPS using the smallest sizes. And this makes sense for things like route and switch processors. Perhaps you are confusing that.

You should reread your link a little more carefully. From your link:

">However it is also important to make sure that the device has the capacity or the ability to switch/route as many packets as required to achieve wire rate performance."

The key phrase there is "as required." Almost nobody needs to sustain forwarding Ethernet frames with empty TCP segments or empty UDP datagrams in them. In fact many vendors will spec for an average size. Since packet size x PPS will give you your throughput, if the average packet size is larger you need much less PPS to achieve line rate.

Just like the sibling, I admit I’ve never heard this definition of line rate...

You're both right. It's an older term from the early 90's when a router's selling point was being able to hit "line rate" with the smallest possible packet size. Example, how many tiny datagrams can you forward to fill that link. Back then, people were still doing lots of routing on general purpose machines and Cisco/Juniper were just starting to get into the high performance game.

These days line-rate just means sending enough traffic to fill the link at whatever rate you want. That's generally good enough for server folk since they just want to get you the cat pics ASAP.

That's not good enough for people running transit networks, since they care more about packets per second performance. Sending huge amounts of data is easy for them; what they really care about is PPS.

Aside, the next generations of router NPU's are trash in terms of PPS performance. I take that back, they're not trash. They're the trash in the dumpsterfire. That's how bad they are. We're fairly screwed there.

My guess is GoDaddy was looking at increased PPS performance either for DNS or maybe building their own DDoS mitigation framework (Arbor gear is pricey).

No, PPS and bandwidth are two distinct metrics. Although there can be a linear relationship between them line rate does not always imply a payload equal or close to the interface MTU. You see this with network vendors and some of the higher end gear. Network vendors always give specs for their gear by quoting both metrics. And there is some gear that that is capable of doing line rates even with small packets, example the Cisco ASR 1000:

"For example, because one of the newest Cisco routers, the Cisco ASR 1000 Series Router, is capable of forwarding packets at up to 16 Mp/s with services enabled, it can support the processing of the equivalent of 10 Gb/s of traffic at line rate, with services, even for small packets."[1]

[1] https://tools.cisco.com/security/center/resources/network_pe...

Does line rate imply smallest packets? For CDN style use cases, you want to use the whole pipe, and it's going to be mostly larger packets.

Yes.

The point of discussion here is that the Linux kernel struggles to do line rate 10Gbps. This was misinterpreted as "the Linux kernel struggles to do 10Gbps".

Reply on news.ycombinator.com