Re: Xen DOM0 pirq panic with lots of cores

[Greg Troxel <gdt%lexort.com@localhost>]

Staffan Thomen <staffan%shangtai.net@localhost> writes:

> 40 an 20 were too many 10 booted. But this might be highly variable from
> how many pseudo-interrupts are needed on the cpus, and these seem to use
> a lot. The standard msgbuf is too small to fit all the boot messages
> for all the stuff going on.

Sounds like you could multiply by 8 and be ok.

> No need to rush to fix this on my account, although I suppose this could
> be made to dynamically reallocate itself either in chunks or singly as
> needed when a new one is discovered? Presumably it's a lookup table that
> is generated on boot and then never changes. Then again I know next to
> nothing about kernel programming and even less of xen, only a suspicion
> that it might be a more restricted environment.

The basic difference inkernel is that you use section 9 interfaces, not
standard C library, and you need to be really thoughtful about
blocking/locking.

If the number of CPUs is known when this is set up, and you can make it
dynamic, that would be a bit hacky but would help a lot.

The other question is if it's really necessary to panic, vs baing able
to fail and just not use some resources.  The system really shouldn't
get into a state like that where it panics from low resources.