CODEWITHSUNDEEP
multicore
user5233244
user5233244

Reputation:

System startup of multicore computer

I would really like to know how does a multicore CPU start when the computer starts up. I imagine there is like a "dominant core" that loads the BIOS and later on ther kernel to RAM and wakes up the rest of the cores leaving them waiting for code to run (like an infinite while loop?). But that it's only how I guess it works.

Other question is, after the kernel is loaded on memory all cores can do system calls, right?. And how does one core control the tasks of the other cores? Which instructions are used? (in x86 / x86-64)

Upvotes: 2

Views: 945

Answers (1)

Zan Lynx
Zan Lynx

Reputation: 54363

Yes there is a boot CPU. The firmware handles that. It's usually CPU 0, but what if that one is missing or defective? Then it gets trickier.

On x86 platforms there's the ACPI tables which describe the CPU and memory layouts. The operating system starts the other CPUs with IPI (inter processor interrupts) which kick them out of idle into the interrupt handlers (which were set in memory) and then into operating system functions. Which then choose threads to run and start doing useful things.

If you really want to know how it all works read the source code for Linux or one of the BSDs.

Update: Looks like I was wrong about IPI. It is using interrupts but not the normal IPI ones. The Linux SMP boot is here: https://github.com/torvalds/linux/blob/master/arch/x86/kernel/smpboot.c

It seems to use NMI or sets the CPU reset.

Upvotes: 2

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