Bug#637308: xen-linux-system-2.6.32-5-xen-amd64: with kernel option 'nosmp', dom0 hangup while init PCI-Express Fusion-MPT SAS

[Ian Campbell <ijc@hellion.org.uk>]

On Wed, 2011-08-10 at 17:08 +0400, Константин Алексеев wrote:
> http://docs.ganeti.org/ganeti/2.2/html/install.html
> "For optimum performance when running both CPU and I/O intensive
> instances, it’s also recommended that the dom0 is restricted to one
> CPU only, for example by booting with the kernel parameter nosmp."
> 
> Also this benchmarking advises disable smp
> http://web2.clarkson.edu/class/cs644/xen/files/repeatedxen-usenix04.pdf

Ignoring whether or not this is good advice (I expect it very much
depends on your workload) this can be better achieved by adding
dom0_max_vcpus=1 to your hypervisor command line or by hot-unplugging
vCPUS once the system has booted (by echoing 0
into /sys/devices/system/cpu/cpu*/online for those CPUs). (the later
give you the option of adding back VCPUs dynamically if you find you
need to)

That said, nosmp really ought to work I suppose so if this still happens
on a recent kernel (e.g. 3.0) then I would appreciate it if you would
also report this issue upstream (see
http://wiki.xen.org/xenwiki/ReportingBugs)

Did you confirm that this doesn't also happen under native? On first
glance it looks more like an issue with a specific driver than a Xen
issue.

Ian.

> 
> 2011/8/10 Ben Hutchings <ben@decadent.org.uk>
>         On Wed, 2011-08-10 at 16:51 +0400, Konstantin Alekseev wrote:
>         > Package: xen-linux-system-2.6.32-5-xen-amd64
>         > Version: 2.6.32-35
>         > Severity: normal
>         >
>         >
>         > With kernel options 'nosmp' dom0 hang
>         [...]
>         
>         Why does this matter to you?
>         
>         Ben.
>         
> 
> 
> 
> -- 
> Konstantin

-- 
Ian Campbell

mixed emotions:
	Watching a bus-load of lawyers plunge off a cliff.
	With five empty seats.