[PATCH v8 24/24] nvme-pci: optimize single-segment handling

[Leon Romanovsky]

On Tue, Apr 22, 2025 at 06:39:56AM +0200, Christoph Hellwig wrote:
> On Fri, Apr 18, 2025 at 09:47:54AM +0300, Leon Romanovsky wrote:
> > From: Kanchan Joshi <joshi.k at samsung.com>
> > 
> > blk_rq_dma_map API is costly for single-segment requests.
> > Avoid using it and map the bio_vec directly.
> 
> This needs to be folded into the earlier patches or split prep patches
> instead of undoing work done earlier, preferably combined with a bit
> of code movement so that the new nvme_try_setup_prp_simple stays in
> the same place as before and the diff shows it reusing code.
> 
> E.g. change
> 
> "nvme-pci: use a better encoding for small prp pool allocations" to
> already use the flags instead of my boolean, and maybe include 
> abort in the flags instead of using a separate bool so that we
> don't increase hte iod size.
> 
> Slot in a new patch after that that dropping the single SGL segment
> fastpath if we think we don't need that, although if we need the PRP
> one I suspect that one would still be very helpful as well.
> 
> Add a patch if we want the try_ version of, although when keeping
> the optimization for SGLs as well that are will look a bit different.

I uploaded new tag dma-split-Apr-22 with the changes. At the end, I
decided to keep SGL optimized path too, but didn't create separate
patch for try_* variants as they require block iterator, which is
introduced in conversion patch only.

> 
> I'm happy to give away my patch authorship credits if that helps with
> the folding.

I kept you as an author. Please advise if I need to change it to be someone else.

Thanks