Hacker News new | ask | show | jobs
by FireBeyond 72 days ago
Once upon a time, Linus would shout and yell about how the kernel should never "break" userspace (and I see in some places, some arguments of "It's not broken, it's just a performance regression" - personally I'd argue a 50% hit to performance of a pre-eminent database engine is ... quite the regression).

Now, the kernel engineer who introduced the brand new mechanism (introduced in Linux 7.0) for handling pre-emption says the "fix" is for Postgres to start using this new mechanism (I think the sister comment below links to what one of the Postgres engineers thinks of that, and I'm inclined mostly to agree).
6 comments
shakna 71 days ago
Freund seems to suggest that hugepages is the right way to run a system under this sort of load - which is the fix.

> Hah. I had reflexively used huge_pages=on - as that is the only sane thing to do with 10s to 100s of GB of shared memory and thus part of all my benchmarking infrastructure - during the benchmark runs mentioned above.

> Turns out, if I disable huge pages, I actually can reproduce the contention that Salvatore reported (didn't see whether it's a regression for me though). Not anywhere close to the same degree, because the bottleneck for me is the writes.

But, they can speak for themselves here [0].

[0] https://news.ycombinator.com/item?id=47646332

link
perching_aix 72 days ago
Entertaining perspective - I thought that the whole "it's not an outage it's a (horizontal or vertical) degradation" thing was exclusive to web services, but thinking about it, I guess it does apply even in cases like this.
link
MBCook 72 days ago
It wouldn’t be the first time one of the other maintainers ran afoul of “Linus’s law“.

He may simply be waiting until more is known on exactly what’s causing it.

link
bear8642 72 days ago
> I'd argue a 50% hit to performance [...] is ... quite the regression

Indeed! Especially if said regression happens to impact anything trade/market related...

link
quietsegfault 72 days ago
This was my immediate thought - kernel doesn’t break software, or at least it didn’t used to.
link
arjie 72 days ago
Well, the reason he'd yell about it is that someone did it. If no one ever did it, he'd never yell and we'd never have the rule. So one can only imagine that this is one of those things where someone has to keep holding the line rather than one of those things where you set some rule and it self-holds.

Doubtless someone will have to do the yelling.

link