[libvirt] [PATCH v3 3/7] qemu monitor: add multithread compress parameters accessors

[Nikolay Shirokovskiy]

On 04.02.2016 21:11, Jiri Denemark wrote:
> On Thu, Jan 28, 2016 at 10:04:29 +0300, Nikolay Shirokovskiy wrote:
>> From: ShaoHe Feng <shaohe.feng at intel.com>
>>
>> Current compression does not use all range of parameter values
>> so let's use some of them as 'unspecified' values. These
>> values will be used to mark parameters that were not specified
>> on migrate command line. Thus we check that qemu does not
>> use these values when we read parameters.
>>
>> Signed-off-by: ShaoHe Feng <shaohe.feng at intel.com>
>> Signed-off-by: Nikolay Shirokovskiy <nshirokovskiy at virtuozzo.com>
>> ---
>>  src/qemu/qemu_monitor.c      |  29 +++++++++++++
>>  src/qemu/qemu_monitor.h      |  16 +++++++
>>  src/qemu/qemu_monitor_json.c |  87 +++++++++++++++++++++++++++++++++++++
>>  src/qemu/qemu_monitor_json.h |   5 +++
>>  src/qemu/qemu_monitor_text.c | 100 +++++++++++++++++++++++++++++++++++++++++++
>>  src/qemu/qemu_monitor_text.h |   5 +++
> 
>>  
>>  
>>  int
>> +qemuMonitorGetMigrationCompressParametersMT(qemuMonitorPtr mon,
>> +                                            qemuMonitorMigrationMTParametersPtr params)
> 
> I think a more general qemuMonitor[GS]etMigrationParameters [gs]etting
> all parameters at once would be a bit better. After all, it all boils
> down to query-migrate-parameters and migrate-set-parameters and having
> separate functions for each group of parameters would mean we'd have to
> call the QMP commands several times.

AFAIK it is not so. We can't set(get) xbzrle options (only size now) and 
multithread options togather. We neet "query-migrate-cache-size" for the
first and "query-migrate-parameters" for the second.

>> +int qemuMonitorJSONSetMigrationCompressParametersMT(qemuMonitorPtr mon,
>> +                                                    qemuMonitorMigrationMTParametersPtr params)
>> +{
>> +    int ret = -1;
>> +    virJSONValuePtr cmd;
>> +    virJSONValuePtr reply = NULL;
>> +
>> +    cmd = qemuMonitorJSONMakeCommand("migrate-set-parameters",
>> +                                     "i:compress-level", params->level,
>> +                                     "u:compress-threads", params->threads,
>> +                                     "u:decompress-threads", params->dthreads,
>> +                                     NULL);
> 
> Is passing an "undefined" value for any of these parameters allowed
> (i.e., will QEMU use a default value) or do we always have to set all of
> them?

QEMU is good enough to take partial parameters specs. In this case the other
just stay untouched. But I never use this command in this mode and specify
all parameters. I do it to make sure we don't get compression parameters
from previous failed migration attempt. See patch number 5. 

Basically instead of reverting parameters on unsuccessful migration
I use hardcoded default values for parameters that are not specified on migration.