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Re: [Xen-devel] RFE: Detect NUMA misconfigurations and prevent machine freezes
- To: Steven Haigh <netwiz@xxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- From: Juergen Gross <jgross@xxxxxxxx>
- Date: Wed, 29 Aug 2018 07:49:40 +0200
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- Delivery-date: Wed, 29 Aug 2018 05:49:53 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
- Openpgp: preference=signencrypt
On 29/08/18 07:33, Steven Haigh wrote:
> When playing with NUMA support recently, I noticed a host would always hang
> when trying to create a cpupool for the second NUMA node in the system.
>
> I was using the following commands:
> # xl cpupool-create name=\"Pool-1\" sched=\"credit2\
> # xl cpupool-cpu-remove Pool-0 node:1
> # xl cpupool-cpu-add Pool-1 node:1
>
> After the last command, the system would hang - requiring a hard reset of the
> machine to fix.
>
> I tried a different variation with the same result:
> # xl cpupool-create name=\"Pool-1\" sched=\"credit2\
> # xl cpupool-cpu-remove Pool-0 node:1
> # xl cpupool-cpu-add Pool-1 12
>
> It turns out that the RAM was installed sub-optimally in this machine. A
> partial output from 'xl info -n' shows:
> numa_info :
> node: memsize memfree distances
> 0: 67584 62608 10,21
> 1: 0 0 21,10
>
> A machine where we could get this working every time shows:
> node: memsize memfree distances
> 0: 34816 30483 10,21
> 1: 32768 32125 21,10
>
> As we can deduce RAM misconfigurations in this scenario, I believe we should
> check to ensure that RAM configuration / layout is sane *before* attempting
> to
> split the system and print a warning.
>
> This would prevent a hard system freeze in this scenario.
RAM placement should not matter here. As the name already suggests
cpupools do assignment of cpus. RAM allocated will be preferred taken
from a local node, but this shouldn't be mandatory for success.
Would it be possible to use a debug hypervisor (e.g. 4.12-unstable) for
generating a verbose log (hypervisor boot parameter "loglvl=all") and
sending the complete hypervisor log?
Juergen
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