Re: [Xen-devel] [PATCH RFC] x86: Add hack to disable "Fake HT" mode

[Jan Beulich <jbeulich@xxxxxxxx>]

On 15.11.2019 16:30, George Dunlap wrote:
> On 11/15/19 3:27 PM, Jan Beulich wrote:
>> On 15.11.2019 16:05, George Dunlap wrote:
>>> FTR, please avoid top-posting. :-)
>>>
>>> On 11/15/19 2:31 PM, Steven Haigh wrote:
>>>> Just regarding the use of a system environment variable to turn this
>>>> feature / bugfix / hack on and off - this would probably break starting
>>>> the VM via the xendomains script.
>>>>
>>>> If the VM definition is in /etc/xen/auto/, then there would be nothing
>>>> to set the environment variable before the VM is launched - hence it
>>>> would not be applied and a guest crash would occur...
>>>>
>>>> Depending on the VM's settings, this would either continue to start &
>>>> crash - or just stop again until it could be started with the ENV variable.
>>>
>>> Right.  So a couple of options:
>>>
>>> 1. Users of xendomains could set the environment variable in their
>>> xendomains script
>>>
>>> 2. We could add a xl.cfg option.  Unknown xl.cfg entries are ignored
>>> (for better or for worse); in the future, when the "fake ht" thing is
>>> replaced, we can either continue ignoring it, or give a useful error
>>> message saying how it should be changed.
>>>
>>> 2a.  We could have the config option *replace* the environment variable;
>>> in which case we'd leave libvirt users high and dry
>>>
>>> 2b. We could have the config option cause xl to *set* the environment
>>> variable, which should continue to allow other toolstacks (even those
>>> not using libxl) to potentially work around the issue.
>>
>> And how would any of these allow to deal with heterogeneous sets of
>> guests?
> 
> Are you perhaps confusing 'xl.cfg' (which is the per-domain
> configuration file) with 'xl.conf' (which is the system-wide
> configuration file)?

Oh, indeed I was. I'm not used to any suffixes on domain config
files. I'm sorry.

Jan

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