Re: [Qemu-devel] [PATCH 05/12] migration: show the statistics of compression

[Xiao Guangrong <guangrong.xiao@gmail.com>]

On 07/17/2018 03:01 AM, Dr. David Alan Gilbert wrote:
> * Xiao Guangrong (guangrong.xiao@gmail.com) wrote:
>>
>>
>> On 06/14/2018 12:25 AM, Dr. David Alan Gilbert wrote:
>>   }
>>>>    static void migration_bitmap_sync(RAMState *rs)
>>>> @@ -1412,6 +1441,9 @@ static void flush_compressed_data(RAMState *rs)
>>>>            qemu_mutex_lock(&comp_param[idx].mutex);
>>>>            if (!comp_param[idx].quit) {
>>>>                len = qemu_put_qemu_file(rs->f, comp_param[idx].file);
>>>> +            /* 8 means a header with RAM_SAVE_FLAG_CONTINUE. */
>>>> +            compression_counters.reduced_size += TARGET_PAGE_SIZE - len + 8;
>>>
>>> I think I'd rather save just len+8 rather than than the subtraction.
>>>
>> Hmmmmmm, is this what you want?
>>        compression_counters.reduced_size += len - 8;
>>
>> Then calculate the real reduced size in populate_ram_info() where we return this
>> info to the user:
>>        info->compression->reduced_size = compression_counters.pages * PAGE_SIZE - compression_counters.reduced_size;
>>
>> Right?
> 
> I mean I'd rather see the actual size presented to the user rather than
> the saving compared to uncompressed.
> 

These statistics are used to help people to see whether compression works efficiently or not,
so maybe reduced-size is more straightforward?　:)