Re: [PATCH 00/12] add per-domain and per-cpupool generic parameters

From: Juergen Gross <jgross@suse.com>
To: George Dunlap <george.dunlap@citrix.com>,
	Jan Beulich <JBeulich@suse.com>
Cc: Stefano Stabellini <sstabellini@kernel.org>,
	Wei Liu <wei.liu2@citrix.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
	George Dunlap <George.Dunlap@eu.citrix.com>,
	Andrew Cooper <andrew.cooper3@citrix.com>,
	Tim Deegan <tim@xen.org>, Dario Faggioli <dfaggioli@suse.com>,
	Julien Grall <julien.grall@arm.com>,
	xen-devel <xen-devel@lists.xenproject.org>,
	Daniel de Graaf <dgdegra@tycho.nsa.gov>,
	Ian Jackson <Ian.Jackson@eu.citrix.com>
Subject: Re: [PATCH 00/12] add per-domain and per-cpupool generic parameters
Date: Tue, 18 Sep 2018 13:30:37 +0200	[thread overview]
Message-ID: <2389f7c7-88b9-b39c-9191-b9a796446a56@suse.com> (raw)
In-Reply-To: <984047f6-4785-27e6-2ff8-63d990a9238a@citrix.com>

On 18/09/18 13:18, George Dunlap wrote:
> On 09/18/2018 12:10 PM, Juergen Gross wrote:
>> On 18/09/18 12:32, Jan Beulich wrote:
>>>>>> On 18.09.18 at 08:02, <jgross@suse.com> wrote:
>>>> Instead of using binary hypervisor interfaces for new parameters of
>>>> domains or cpupools this patch series adds support for generic text
>>>> based parameter parsing.
>>>>
>>>> Parameters are defined via new macros similar to those of boot
>>>> parameters. Parsing of parameter strings is done via the already
>>>> existing boot parameter parsing function which is extended a little
>>>> bit.
>>>>
>>>> Parameter settings can either be specified in configuration files of
>>>> domains or cpupools, or they can be set via new xl sub-commands.
>>>
>>> Without having looked at any of the patches yet (not even their
>>> descriptions) I'm still wondering what the benefit of textual parameters
>>> really is: Just like "binary" ones, they become part of the public
>>> interface, and hence subsequently can't be changed any more or
>>> less than the ones we currently have (in particular, anything valid in
>>> a guest config file will imo need to remain to be valid and meaningful
>>> down the road).
>>
>> So lets look what would be needed for adding something like the
>> per-domain xpti parameter using binary interfaces:
>>
>> 1 an extension of some domctl interface, maybe bumping of the domctl
>>   interface version
>> 2 adding the logic to domctl handling
>> 3 adding libxc support
>> 4 adding libxl support
>> 5 adding a new xl sub-command
>> 6 adding domain config support
>> 7 adding documentation
>>
>> With my approach only 2 (in a modified form, parameter handling instead
>> of domctl, but comparable in the needed effort) and 7 are needed.
>>
>> So once the framework is in place it is _much_ easier to add new
>> features.
> 
> So the idea here is that you pass a full hypervisor command-line style
> string into a hypercall -- say, "credit2_cap_period_ms=5"?

Yes.

I guess it would be questionable to have multiple ways to set a
property, so only new properties should be supported.

Juergen

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