The Linux kernel has been accidentally hardcoded to a maximum of 8 cores
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Re: The Linux kernel has been accidentally hardcoded to a maximum of 8 cores
#2> The Linux kernel has been accidentally hardcoded to a maximum of 8 cores for the past 15 years and nobody noticed
I can understand having a bug like that, but unnoticed for 15 years? more than 8 cores was rare 15 years ago, and as a percentage of chips sold is still rare, but presumably people with threadrippers ran benchmarks? optimized? etc? just doesn't seem possible
Re: The Linux kernel has been accidentally hardcoded to a maximum of 8 cores
#3> The Linux kernel has been accidentally hardcoded to a maximum of 8 cores for the past 15 years and nobody noticed I can understand having a bug like that, but unnoticed for 15 years? more than 8 cores was rare 15 years ago, and as a percentage of chips sold is still rare, but presumably people with threadrippers ran benchmarks? optimized? etc? just doesn't seem possible
Yeah how come people running massive computers didn’t notice the limit?
Re: The Linux kernel has been accidentally hardcoded to a maximum of 8 cores
#4> The Linux kernel has been accidentally hardcoded to a maximum of 8 cores for the past 15 years and nobody noticed I can understand having a bug like that, but unnoticed for 15 years? more than 8 cores was rare 15 years ago, and as a percentage of chips sold is still rare, but presumably people with threadrippers ran benchmarks? optimized? etc? just doesn't seem possible
Yeah how come people running massive computers didn’t notice the limit?
If i skimmed this correctly then its a malus on performance not a complete cliff. I guess people just thought "hohum - there gotta be some overhead in scheduling".
Re: The Linux kernel has been accidentally hardcoded to a maximum of 8 cores
#5> The Linux kernel has been accidentally hardcoded to a maximum of 8 cores for the past 15 years and nobody noticed I can understand having a bug like that, but unnoticed for 15 years? more than 8 cores was rare 15 years ago, and as a percentage of chips sold is still rare, but presumably people with threadrippers ran benchmarks? optimized? etc? just doesn't seem possible
Yeah how come people running massive computers didn’t notice the limit?
Because it's a misleading headline and doesn't mean linux only used 8 cores for computing for 15 years.
Re: The Linux kernel has been accidentally hardcoded to a maximum of 8 cores
#6I'm a bit disappointed and slightly annoyed that this was published without a comment from any of the Kernel maintainers.
Re: The Linux kernel has been accidentally hardcoded to a maximum of 8 cores
#7Is there a kernel maintainer here who can weigh in on the implications of this?
Re: The Linux kernel has been accidentally hardcoded to a maximum of 8 cores
#8Earlier quoted context omitted.
Yeah how come people running massive computers didn’t notice the limit?
If i skimmed this correctly then its a malus on performance not a complete cliff. I guess people just thought "hohum - there gotta be some overhead in scheduling".
Yes, when you run in parallel, and e.g. see all >8 cores nicely nagging up to 100% why assume something wrong?
Still don't get after rereading the article, what is the malus, it must be small by that? Because you definitely saw linear scaling with parallelizable problems on >8 cores, otherwise people would have noticed?
Re: The Linux kernel has been accidentally hardcoded to a maximum of 8 cores
#9> The Linux kernel has been accidentally hardcoded to a maximum of 8 cores for the past 15 years and nobody noticed I can understand having a bug like that, but unnoticed for 15 years? more than 8 cores was rare 15 years ago, and as a percentage of chips sold is still rare, but presumably people with threadrippers ran benchmarks? optimized? etc? just doesn't seem possible
Because it’s a completely misleading headline.
The number of cores in the heuristic used to calculate task switch frequency was capped to 8.
This is a reasonable thing to do as a heuristic, because you don’t want your time slice to grow indefinitely with core count on an interactive system.
Re: The Linux kernel has been accidentally hardcoded to a maximum of 8 cores
#10> The Linux kernel has been accidentally hardcoded to a maximum of 8 cores for the past 15 years and nobody noticed I can understand having a bug like that, but unnoticed for 15 years? more than 8 cores was rare 15 years ago, and as a percentage of chips sold is still rare, but presumably people with threadrippers ran benchmarks? optimized? etc? just doesn't seem possible
It's possible, the kernel itself not using more than 8 cores will be imperceptible except on things like network devices where theres' no userlandkernel barrier. In those kinds of high-throughput applications usually you offload things the kernel does to hardware anyway.
You'll lose your mind once you realise that Windows NT handles a lot of things single-threaded. I had a situation once where I was handling a few million packets per second of TCP on Windows and it only pins a single core.
Though: that's not what TFA is looking at: in this case you're not actually limited to 8 cores, you're limited to slicing your executions into 8 parts per cpu per "tick".
This is a known way of scheduling, you only get 1/8th of a tick with a fair scheduler.