Re: [Qemu-devel] migration: adding migration to/from a file (v2)

[Anthony Liguori]

Jamie Lokier wrote:
> > Remember, migration is a streaming 
> > protocol, not a random access, so it only makes sense to have one 
> > outstanding request at a time.
> >     
>
> Fwow, often with streaming (in general) the highest performance comes
> from having two or more outstanding requests at a time, so there are
> no gaps between requests being processed at the OS and device level.
>
> However, unless migrate-to-file uses O_DIRECT that will be hidden by
> the OS's buffering.
>   

It's already buffered FWIW by the savevm infrastructure.  You'll won't 
usually see small operations.

Regards,

Anthony Liguori

> Then the remaining overhead from AIOs (or fake AIOs using threads) is
> lots context switching, one per write completed.
>
> -- Jamie
>
>
>