Re: [Qemu-devel] [PATCH V2] add migration capability to bypass the shared memory

[Lai Jiangshan]

On Thu, Aug 11, 2016 at 3:11 PM, Li, Liang Z <address@hidden> wrote:
>> >>
>> >> I might have missed something, could you tell me more?
>> >>
>> >> void bitmap_set(unsigned long *map, long start, long nr); I think the
>> >> @start and @nr are both the number of the bits.
>> >>
>> >> thanks,
>> >> Lai
>> >
>> > You are right,  I have make a mistake by checking the code. Sorry for the
>> noise.
>> >
>> > BTW. Is it possible to bypass the shared block in the
>> 'ram_find_and_save_block'?
>> > I mean no to check if a page is dirty for a shared block, it may make 
>> > things
>> faster.
>>
>> Nice spotted.  That would make things faster.  But once there we could split
>> the bitmap by ramblock, and the migration_dirty_pages also per block, that
>> would make all the searchs faster, and adding/removing blocks of ram much
>> easier.  If we enter optimizing that function, we could really do much better
>> that the "again" parameter that we have right now.
>>
>> Later, Juan.


This patch focuses on the core thing: adding the ability to bypass
migrating the memory.
I don't want to add further optimization for it now.
I hope this patch merged solo and earlier.
optimization patches can be sent after this patch accepted.

>
> Did some experiment with an 8GB VM.
> Total time: 93ms
> Setup: 70ms
> Downtime: 6ms
>
> So most of the time spend on Setup stage, and most of the time spend on
> setup stage is starting dirty page logging.
> How about not start dirty page logging for shared blocks? then it's possible
> to shorten the total time to about 30ms.

bypass migrating the memory includes
  bypass copying&sending the memory (this patch, save seconds)
  bypass dirty page logging (save ten of milliseconds)
  bypass other thing??

30ms is a huge part of the 130ms of the hyperhq cases.
We definitely need it, I once tried it at the beginning, but it is a
little complicated for me. So I focus the the major part now.

Thanks,
Lai




>
> Liang
>
>
>
>
>