Re: [Qemu-devel] [v4 12/13] migration: Add command to set migration parameter

[Eric Blake]

On 02/03/2015 06:26 PM, Li, Liang Z wrote:

>> Hmm - do we really need two parameters here?  Remember, compress
>> threads is used only on the source, and decompress threads is used only on
>> the destination.  Having a single parameter, 'threads', which is set to
>> compression threads on source and decompression threads on destination,
>> and which need not be equal between the two machines, should still work,
>> right?
>>
> 
> Yes, it works. The benefit of using one parameter instead of two can reduce 
> the QMP 
> command count, and the side effect of using the same thread count for 
> compression
>  and decompression is a little waste if the user just want to use the default 
> settings,
> you know, decompression is usually  about 4 times faster than compression.  
> Use more
> decompression threads than needed will waste some RAM which used to save data 
> structure related to the decompression thread, about 4K bytes RAM per thread, 
> is it 
> acceptable?

The default setting is no compression.  The user already has to
configure things on both sides to get compression, so it is not a burden
to ask them to configure thread count on both sides correctly.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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