Re: [dpdk-dev] [PATCH] vhost: improve dirty pages logging performance

[Maxime Coquelin <maxime.coquelin@redhat.com>]

Hi Tiwei,

I just see I missed to reply to your comment on my commit message:

On 05/03/2018 01:56 PM, Tiwei Bie wrote:
> On Mon, Apr 30, 2018 at 05:59:54PM +0200, Maxime Coquelin wrote:
>> This patch caches all dirty pages logging until the used ring index
>> is updated. These dirty pages won't be accessed by the guest as
>> long as the host doesn't give them back to it by updating the
>> index.
> Below sentence in above commit message isn't the reason why
> we can cache the dirty page logging. Right?
> 
> """
> These dirty pages won't be accessed by the guest as
> long as the host doesn't give them back to it by updating the
> index.

That's my understanding.
As long as the used index is not updated, the guest will not process
the descs.
If the migration converges between the time the descs are written,
and the time the used index is updated on source side. Then the guest
running on destination will not see the descriptors as used but as
available, and so will be overwritten by the vhost backend on
destination.

Regards,
Maxime