Meanwhile the best network I’ve ever benchmarked was AWS and measured about 55µs for a round trip!
What on earth are you using that gets you down to single digits!?
What on earth are you using that gets you down to single digits!?
What is "a network" here?
Few infrastructures are optimised for latency, most are geared toward providing high throughput instead.
In fact, apart from HFT, I don't think most businesses are all that latency sensitive. Most infrastructure providers will give you SLAs of high single or low double digits microseconds from Mahwa/Carteret to NY4, but these are private/dedicated links. There's little point to optimising latency when your network ends up on internet where the smallest hops are milliseconds away.
That's just plain wrong. Lower latency always improves everything. Not just responsiveness, but also bandwidth! Because of TCP slow-start and congestion control algorithms, lower latency directly results in higher throughputs.
Not to mention that these latencies add up, which is especially important with chatty microservices applications. Don't forget that typical TCP+HTTPS connections require something like 5 round trips, and that's assuming that the DNS record is already cached! Add in firewalls, load balancers, proxies, side-cars, ingress, and who knows what else, suddenly you're staring down the barrel of 15 millisecond latencies before the data can exit the data centre.
The threshold for "instant" response is 16.7 ms end-to-end, including refreshing the HTML DOM and painting pixels to the screen.
Google and AWS knows this, which is why their data centre networking have ~50µs latencies, some of the best in the industry.
Everyone else: "Nah, don't bother!"
Yet, that doesn't mean latency is at the same priority spot on everyone's list. If you're using TCP on internet, you have already put latency far down in your concerns. That doesn't make you _not want_ better latency, but that does make it a _nice to have_.
There's no obvious shortcut to latency that doesn't involve either loosing on reliability (not requiring ordered messages, not re-requesting dropped messages), or loosing throughput (not assembling small messages on bigger ones), or limiting yourself to private links.
If you do all the above (as in TCP over the internet), then you've made no sacrifice for latency over throughput and resiliency, which to me makes latency a nice to have, but certainly not a primary concern.
If you're working in AWS, you almost certainly are hitting a router, which is comparably slower. Not to mention you are dealing with virtualized hardware, and you are probably sharing all the switches & routers along your path (if someone else's packet is ahead of yours in the queue, you have to wait).
I know that "in principle" the physics of the cabling allows single digit microseconds, but I've never seen it anywhere near that low even with cross-over cables with zero switches in-path!
Switches in these scenarios (e.g. 25GE DC targeted) are pretty predictable and add <1μs (unless misconfigured)
I've never seen this in practice. Maaaaybe with Infiniband and custom-written apps that use a proprietary SDK.
I'd love to see references to actual benchmarks.
this is xilinux/mellanox cards with kernel bypass and cut-through switches with busy-waiting
in reality, in a prod system
I wouldn't rate them as "complete shit".