Re: [PATCH] mbuf: add mbuf physical address field to dynamic field

[Olivier Matz <olivier.matz@6wind.com>]

Hi,

On Thu, Jun 30, 2022 at 05:55:21PM +0100, Bruce Richardson wrote:
> On Thu, Jun 30, 2022 at 09:55:16PM +0530, Shijith Thotton wrote:
> > If all devices are configured to run in IOVA mode as VA, physical
> > address field of mbuf (buf_iova) won't be used. In such cases, buf_iova
> > space is free to use as a dynamic field. So a new dynamic field member
> > (dynfield2) is added in mbuf structure to make use of that space.
> > 
> > A new mbuf flag RTE_MBUF_F_DYNFIELD2 is introduced to help identify the
> > mbuf that can use dynfield2.
> > 
> > Signed-off-by: Shijith Thotton <sthotton@marvell.com>
> > ---
> I disagree with this patch. The mbuf should always record the iova of the
> buffer directly, rather than forcing the drivers to query the EAL mode.
> This will likely also break all vector drivers right now, as they are
> sensitive to the mbuf layout and the position of the IOVA address in the
> buffer.

I have the same opinion than Stephen and Bruce. This field is widely used
in DPDK, I don't think it is a good idea to disable it if some conditions
are met.