Re: [Qemu-devel] [PATCH v3 0/9] Migration: Remove copying of guest ram pages

[Orit Wasserman]

On 03/21/2013 07:12 PM, Paolo Bonzini wrote:
> Il 21/03/2013 17:05, Orit Wasserman ha scritto:
>> In migration all data is copied to a static buffer in QEMUFile,
>> this hurts our network bandwidth and CPU usage especially with large guests.
>> We switched to iovec for storing different buffers to send (even a byte 
>> field is
>> considered as a buffer) and use writev to send the iovec.
>> writev was chosen (as apposed to sendmsg) because it supprts non socket fds.
>>   
>> Guest memory pages are not copied by calling a new function 
>> qemu_put_buffer_no_copy.
>> The page header data and device state data are still copied into the static
>> buffer. This data consists of a lot of bytes and integer fields and the 
>> static
>> buffer is used to store it during batching.
>> Another improvement is changing qemu_putbe64/32/16 to create a single
>> buffer instead of several byte sized buffer.
>>
>> git repository: git://github.com/oritwas/qemu.git sendv_v2
>>
>> Change from v2:
>> Always send data for the iovec even if writev_buffer is not implemented.
>> Coalesce adjacent iovecs to create one big buffer from small adjacent buffer.
>>
>> Changes from v1:
>> Use iov_send for socket.
>> Make writev_buffer optional and if it is not implemented use put_buffer
> 
> I didn't review it too closely, so I don't feel like giving my
> Reviewed-by.  Still, I must say it is a very nice and simple solution.
> Kudos!
> 
> Just one question: patch 6 is not strictly needed anymore now that you
> have coalescing, no?  Should Juan leave it out?
true, Juan had a small fix so I'm sending v4 I will remove it.
> 
> Paolo
>