On 10/09/2018 04:12 PM, Wei Liu wrote:
> On Tue, Oct 02, 2018 at 04:49:26PM +0100, George Dunlap wrote:
>> Commit 3b4adba ("tools/libxl: include scheduler parameters in the
>> output of xl list -l") added scheduling parameters to the set of
>> information collected by libxl_retrieve_domain_configuration(), in
>> order to report that information in `xl list -l`.
>>
>> Unfortunately, libxl_retrieve_domain_configuration() is also called by
>> the migration / save code, and the results passed to the restore /
>> receive code. This meant scheduler parameters were inadvertently
>> added to the migration stream, without proper consideration for how to
>> handle corner cases. The result was that if migrating from a host
>> running one scheduler to a host running a different scheduler, the
>> migration would fail with an error like the following:
>>
>> libxl: error: libxl_sched.c:232:sched_credit_domain_set: Domain 1:Getting
>> domain sched credit: Invalid argument
>> libxl: error: libxl_create.c:1275:domcreate_rebuild_done: Domain 1:cannot
>> (re-)build domain: -3
>>
>> Luckily there's a fairly straightforward way to set parameters in a
>> "best-effort" fashion. libxl provides a single struct containing the
>> parameters of all schedulers, as well as a parameter specifying which
>> scheduler. Parameters not used by a given scheduler are ignored.
>> Additionally, the struct contains a parameter to specify the
>> scheduler. If you specify a specific scheduler,
>> libxl_domain_sched_params_set() will fail if there's a different
>> scheduler. However, if you pass LIBXL_SCHEDULER_UNKNOWN, it will use
>> the value of the current scheduler for that domain.
>>
>> In domcreate_stream_done(), before calling libxl__build_post(), set
>> the scheduler to LIBXL_SCHEDULER_UNKNOWN. This will propagate
>> scheduler parameters from the previous instantiation on a best-effort
>> basis.
>>
>> Signed-off-by: George Dunlap <george.dun...@citrix.com>
>> ---
>> CC: Ian Jackson <ian.jack...@citrix.com>
>> CC: Wei Liu <wei.l...@citrix.com>
>> CC: Andrew Cooper <andrew.coop...@citrix.com>
>> CC: Jan Beulich <jbeul...@suse.com>
>> CC: Dario Faggioli <dfaggi...@suse.com>
>> CC: Juergen Gross <jgr...@suse.com>
>> ---
>> tools/libxl/libxl_create.c | 9 +++++++++
>> 1 file changed, 9 insertions(+)
>>
>> diff --git a/tools/libxl/libxl_create.c b/tools/libxl/libxl_create.c
>> index dcfde7787e..caf79d4620 100644
>> --- a/tools/libxl/libxl_create.c
>> +++ b/tools/libxl/libxl_create.c
>> @@ -1237,6 +1237,15 @@ static void domcreate_stream_done(libxl__egc *egc,
>> ret = ERROR_INVAL;
>> goto out;
>> }
>> +
>> + /*
>> + * The scheduler on the sending domain may be different than the
>> + * scheduler running here. Setting the scheduler to UNKNOWN will
>> + * cause the code to take to take whatever parameters are
>> + * available in that scheduler, while discarding the rest.
>> + */
>> + info->sched_params.sched = LIBXL_SCHEDULER_UNKNOWN;
>
> But this function is called by normal domain creation as well. What if
> libxl user does set the parameter?
Is it? I thought the `stream` meant it was only called when doing
migrate / resume.
-George
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