[PATCH] nvme-pci: always use blk_map_iter for metadata

[Keith Busch]

On Mon, Oct 27, 2025 at 08:13:53AM +0100, Christoph Hellwig wrote:
> On Sun, Oct 26, 2025 at 09:25:51AM +0200, Leon Romanovsky wrote:
> > > Maybe the data path should only use blk_dma_iter too. Is dma_map_bvec
> > > that much faster for the single vector case? I'm going to test both on
> > > real hardware and see if there's a difference in CPU utilization or
> > > latency.
> > 
> > We tried that path (remove special case for single segment), but for
> > very performance oriented case: direct mode without IOMMU, no p2p and
> > extremely powerful RAID (~94M IOPS), Jens and Kanchan saw performance
> > drop. On consumer grade HW (~2M IOPS), the performance change was not
> > noticed.
> 
> Yes.  Sorry, I wanted to reply something like this to Keith earlier but
> managed to drop the ball.

Yeah, no problem. I was reaching the same conclusion anyway and moved on.