Re: [PATCH v5 7/8] multifd: Add multifd-zstd-level parameter

[Markus Armbruster <armbru@redhat.com>]

"Dr. David Alan Gilbert" <dgilbert@redhat.com> writes:

> * Juan Quintela (quintela@redhat.com) wrote:
>> Signed-off-by: Juan Quintela <quintela@redhat.com>
>> ---
>>  migration/migration.c | 15 +++++++++++++++
>>  monitor/hmp-cmds.c    |  4 ++++
>>  qapi/migration.json   | 29 ++++++++++++++++++++++++++---
>>  3 files changed, 45 insertions(+), 3 deletions(-)
>> 
>> diff --git a/migration/migration.c b/migration/migration.c
>> index 3b081e8147..b690500545 100644
>> --- a/migration/migration.c
>> +++ b/migration/migration.c
>> @@ -91,6 +91,8 @@
>>  #define DEFAULT_MIGRATE_MULTIFD_METHOD MULTIFD_METHOD_NONE
>>  /*0: means nocompress, 1: best speed, ... 9: best compress ratio */
>>  #define DEFAULT_MIGRATE_MULTIFD_ZLIB_LEVEL 1
>> +/* 0: means nocompress, 1: best speed, ... 20: best compress ratio */
>> +#define DEFAULT_MIGRATE_MULTIFD_ZSTD_LEVEL 1
>>  
>>  /* Background transfer rate for postcopy, 0 means unlimited, note
>>   * that page requests can still exceed this limit.
>> @@ -805,6 +807,8 @@ MigrationParameters *qmp_query_migrate_parameters(Error **errp)
>>      params->multifd_method = s->parameters.multifd_method;
>>      params->has_multifd_zlib_level = true;
>>      params->multifd_zlib_level = s->parameters.multifd_zlib_level;
>> +    params->has_multifd_zstd_level = true;
>> +    params->multifd_zstd_level = s->parameters.multifd_zstd_level;
>
> Do we really want different 'multifd_...._level's or just one
> 'multifd_compress_level' - or even just reuse the existing
> 'compress-level' parameter.

compress-level, multifd-zlib-level, and multifd-zstd-level apply
"normal" live migration compression, multifd zlib live migration
compression, and multifd zstd live migration compression, respectively.

Any live migration can only use one of the three compressions.

Correct?

> The only tricky thing about combining them is how to handle
> the difference in allowed ranges;  When would the right time be
> to check it?
>
> Markus/Eric: Any idea?

To have an informed opinion, I'd have to dig through the migration
code.

Documentation of admissible range will become a bit awkward, too.

Too many migration parameters...