Re: [Xen-devel] Runtime adjustment of hypervisor parameters

[Juergen Gross <jgross@xxxxxxxx>]

On 04/08/17 15:23, Andrew Cooper wrote:
> On 04/08/17 14:20, Juergen Gross wrote:
>> Last year Jan posted a patch series to change hypervisor log level
>> thresholds via xl command [1]. This approach was later modified by Wei
>> resulting in patch series [2].
>>
>> I'd like to follow up with another approach being able to do the same,
>> but being much more flexible:
>>
>> Instead of controlling only loglvl I suggest to add a xl command
>>
>> xl xen-param <parameters>
>>
>> which will take a <parameters> string being parsed by the hypervisor
>> the same way it is parsing boot parameters. Allowed parameters are
>> specified in the hypervisor the same way as boot parameters, but with
>> another set of macros (e.g. custom_runtime_param(), ...). Often enough
>> (e.g. in the loglvl case) the definitions could be just the same, while
>> in other cases they might differ a little bit (example: conring_size
>> would require a different handling as at boot time due to race
>> condition handling).
>>
>> Parsing functions could be reused in most cases, they'd just need to
>> lose the __init modifier.
>>
>> What do you think: is this approach sensible, or can I just put it into
>> /dev/null instead of starting with the patches?
> 
> What sort of parameters were you thinking of tweaking?  (Without any
> evidence) I'm going to go out on a limb and say that most of the
> hypervisor command line parameters are not safe to play with after boot.

The following would be a nice start for discussion:

async-show-all, console_timestamps, conswitch, guest_loglvl, loglvl,
hvm_debug, hvm_fep, hvm_port80, iommu_dev_iotlb_timeout, irq_ratelimit,
nmi, noreboot, reboot, sync_console, vpmu, watchdog_timeout


Juergen

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