[dpdk-dev] [EXT] Re: [PATCH v12 0/2] add IOVA=VA mode support

[Ferruh Yigit]

>> Hi Vasim, Jerin,
>>
>> Overall looks good and I not getting any functional error but I am observing a
>> huge performance drop with this update, 3.8Mpps to 0.7Mpps [1].	
> 
> Hi Ferruh,
> When it comes to actual kernel netdev test cases  like iperf or any other use cases, there would not be any impact on performance. I think synthetic test case like loopback mode might not be the actual test case alone to depend on when the kernel module is featured to work with kind of devices(pdev or vdev). Users can always fallback to pa mode with cmd line option.
> 
> Please suggest your thoughts on considering what test case to use & evaluate the performance difference.

Hi Vasim,

I also assume the real life test cases will be affected less, but the loopback
performance testing is good to show performance impact of the change.

(Stephen's predictions that KNI is not as fast as tun/tap are getting more real
by time J)

At least I think the possible performance drop and how to mitigate it should be
documented both in release notes and kni documentation.

For the final decision, I am not objecting it but I would like to see more ack
from community to confirm that we trade off iova=va functionality against
performance.

@Jerin, @Thomas, should we conclude this in techboard? Perhaps we can get it for
rc2 and drop it back if rejected in techboard?


Regards,
ferruh