linux-kernel - Re: [PATCH] scatterlist: Speed up for_each

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Date:   Mon, 28 Oct 2019 09:28:16 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Jason Gunthorpe <jgg@...pe.ca>
Cc:     Sultan Alsawaf <sultan@...neltoast.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Thomas Hellstrom <thellstrom@...are.com>,
        Palmer Dabbelt <palmer@...ive.com>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Ming Lei <ming.lei@...hat.com>,
        Gal Pressman <galpress@...zon.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] scatterlist: Speed up for_each_sg() loop macro

On Mon, Oct 28, 2019 at 01:23:20PM -0300, Jason Gunthorpe wrote:
> This testing is making assumptions about how 'nr' is used and the
> construction of the sgl though
> 
> If any chains are partially populated, or for some reason the driver
> starts at a different sgl, it will break. You'll need to somehow
> show none of those possibilities are happening.

And there is nothing forcing a particular layout, there just happens
to be a layout that the generic allocator gives you.  I'm not even
sure the original patch handles the SCSI case of small inlines segments
properly.