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


  • To: Wei Liu <wei.liu2@xxxxxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxx>
  • From: Juergen Gross <jgross@xxxxxxxx>
  • Date: Wed, 19 Sep 2018 19:58:50 +0200
  • Autocrypt: addr=jgross@xxxxxxxx; prefer-encrypt=mutual; keydata= xsBNBFOMcBYBCACgGjqjoGvbEouQZw/ToiBg9W98AlM2QHV+iNHsEs7kxWhKMjrioyspZKOB ycWxw3ie3j9uvg9EOB3aN4xiTv4qbnGiTr3oJhkB1gsb6ToJQZ8uxGq2kaV2KL9650I1SJve dYm8Of8Zd621lSmoKOwlNClALZNew72NjJLEzTalU1OdT7/i1TXkH09XSSI8mEQ/ouNcMvIJ NwQpd369y9bfIhWUiVXEK7MlRgUG6MvIj6Y3Am/BBLUVbDa4+gmzDC9ezlZkTZG2t14zWPvx XP3FAp2pkW0xqG7/377qptDmrk42GlSKN4z76ELnLxussxc7I2hx18NUcbP8+uty4bMxABEB AAHNHkp1ZXJnZW4gR3Jvc3MgPGpncm9zc0BzdXNlLmRlPsLAeQQTAQIAIwUCU4xw6wIbAwcL CQgHAwIBBhUIAgkKCwQWAgMBAh4BAheAAAoJELDendYovxMvi4UH/Ri+OXlObzqMANruTd4N zmVBAZgx1VW6jLc8JZjQuJPSsd/a+bNr3BZeLV6lu4Pf1Yl2Log129EX1KWYiFFvPbIiq5M5 kOXTO8Eas4CaScCvAZ9jCMQCgK3pFqYgirwTgfwnPtxFxO/F3ZcS8jovza5khkSKL9JGq8Nk czDTruQ/oy0WUHdUr9uwEfiD9yPFOGqp4S6cISuzBMvaAiC5YGdUGXuPZKXLpnGSjkZswUzY d9BVSitRL5ldsQCg6GhDoEAeIhUC4SQnT9SOWkoDOSFRXZ+7+WIBGLiWMd+yKDdRG5RyP/8f 3tgGiB6cyuYfPDRGsELGjUaTUq3H2xZgIPfOwE0EU4xwFgEIAMsx+gDjgzAY4H1hPVXgoLK8 B93sTQFN9oC6tsb46VpxyLPfJ3T1A6Z6MVkLoCejKTJ3K9MUsBZhxIJ0hIyvzwI6aYJsnOew cCiCN7FeKJ/oA1RSUemPGUcIJwQuZlTOiY0OcQ5PFkV5YxMUX1F/aTYXROXgTmSaw0aC1Jpo w7Ss1mg4SIP/tR88/d1+HwkJDVW1RSxC1PWzGizwRv8eauImGdpNnseneO2BNWRXTJumAWDD pYxpGSsGHXuZXTPZqOOZpsHtInFyi5KRHSFyk2Xigzvh3b9WqhbgHHHE4PUVw0I5sIQt8hJq 5nH5dPqz4ITtCL9zjiJsExHuHKN3NZsAEQEAAcLAXwQYAQIACQUCU4xwFgIbDAAKCRCw3p3W KL8TL0P4B/9YWver5uD/y/m0KScK2f3Z3mXJhME23vGBbMNlfwbr+meDMrJZ950CuWWnQ+d+ Ahe0w1X7e3wuLVODzjcReQ/v7b4JD3wwHxe+88tgB9byc0NXzlPJWBaWV01yB2/uefVKryAf AHYEd0gCRhx7eESgNBe3+YqWAQawunMlycsqKa09dBDL1PFRosF708ic9346GLHRc6Vj5SRA UTHnQqLetIOXZm3a2eQ1gpQK9MmruO86Vo93p39bS1mqnLLspVrL4rhoyhsOyh0Hd28QCzpJ wKeHTd0MAWAirmewHXWPco8p1Wg+V+5xfZzuQY0f4tQxvOpXpt4gQ1817GQ5/Ed/wsDtBBgB CAAgFiEEhRJncuj2BJSl0Jf3sN6d1ii/Ey8FAlrd8NACGwIAgQkQsN6d1ii/Ey92IAQZFggA HRYhBFMtsHpB9jjzHji4HoBcYbtP2GO+BQJa3fDQAAoJEIBcYbtP2GO+TYsA/30H/0V6cr/W V+J/FCayg6uNtm3MJLo4rE+o4sdpjjsGAQCooqffpgA+luTT13YZNV62hAnCLKXH9n3+ZAgJ RtAyDWk1B/0SMDVs1wxufMkKC3Q/1D3BYIvBlrTVKdBYXPxngcRoqV2J77lscEvkLNUGsu/z W2pf7+P3mWWlrPMJdlbax00vevyBeqtqNKjHstHatgMZ2W0CFC4hJ3YEetuRBURYPiGzuJXU pAd7a7BdsqWC4o+GTm5tnGrCyD+4gfDSpkOT53S/GNO07YkPkm/8J4OBoFfgSaCnQ1izwgJQ jIpcG2fPCI2/hxf2oqXPYbKr1v4Z1wthmoyUgGN0LPTIm+B5vdY82wI5qe9uN6UOGyTH2B3p hRQUWqCwu2sqkI3LLbTdrnyDZaixT2T0f4tyF5Lfs+Ha8xVMhIyzNb1byDI5FKCb
  • Cc: Tim Deegan <tim@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>, George Dunlap <George.Dunlap@xxxxxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>, Dario Faggioli <dfaggioli@xxxxxxxx>, Julien Grall <julien.grall@xxxxxxx>, Jan Beulich <JBeulich@xxxxxxxx>, xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Daniel de Graaf <dgdegra@xxxxxxxxxxxxx>
  • Delivery-date: Wed, 19 Sep 2018 17:59:05 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
  • Openpgp: preference=signencrypt

On 19/09/18 19:28, Wei Liu wrote:
> On Tue, Sep 18, 2018 at 02:25:04PM +0100, George Dunlap wrote:
>> On 09/18/2018 12:32 PM, Juergen Gross wrote:
>>> On 18/09/18 13:20, Jan Beulich wrote:
>>>>>>> On 18.09.18 at 13:10, <jgross@xxxxxxxx> wrote:
>>>>> On 18/09/18 12:32, Jan Beulich wrote:
>>>>>>>>> On 18.09.18 at 08:02, <jgross@xxxxxxxx> 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.
>>>>
>>>> All the above would hold if the individual options were expressed as
>>>> e.g. flags in an extensible bit vector.
>>>
>>> Who would translate the new option into a bit vector? This would be the
>>> tools (libxc/libxl/xl), so those need to be modified for each new bit.
>>
>> A bit vector would only allow on/off; it wouldn't allow you to set
>> numeric parameters, for example.
>>
>> I like the idea of being able to add configuration parameters without
>> having a huge amount of boilerplate; and also of being able to backport
>> parameters like xpti without having to worry so much about compatibility.
>>
>> But I'm not a fan of the idea of using a "string blob" to accomplish
>> that.  It's convenient for the exact use case you seem to be
>> contemplating: having a user add the string into the xl config file, and
>> having nobody but the hypervisor interpret it.  But what about tools
>> that may want to set that parameter?  Or tools that want to query the
>> parameter, or "introspect" on the domain settings or whatever?  Now they
>> have to have a bunch of code to generate and parse the string code.
>>
> 
> Having the ability to query parameters is a must. Suppose you change
> some settings while the domain is running, in order to re-create domain
> with the same parameter (migration) there must be a way for toolstack to
> query the current settings of that domain. I think most if not all
> information is retrieved from xen using binary interface.
> 
> Furthermore, if the string blob is not stored in xen, and there isn't a
> binary interface for *setting* parameters, toolstack will have to
> translate the retrieved binary information into strings again.
> 
> I'm not picky about formats, but please make get and set interfaces
> symmetric (use the same representation).

Did you look into the patches, especially patch 10? The parameters set
are all stored in domain config via libxl__arch_domain_save_config().

This is skipped only with the user specifying a special flag for
"xl domain-set-parameters".


Juergen

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