Re: [PATCH V2] net/mlx4: Get rid of page operation after dma_alloc_coherent

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On 12/19/18 12:25 AM, Christoph Hellwig wrote:
On Tue, Dec 18, 2018 at 05:12:41PM -0700, Stephen Warren wrote:
On 12/18/18 1:56 PM, Christoph Hellwig wrote:
This goes in the right direction, but I think we need to stop
abusing the scatterlist for the coherent mapping entirely.  Something
like the patch below (based on yours):

Oh, it was simple to get rid of the sg list usage than I thought; I'd
assume it would be touched in a bunch of other files.

I had to make the additions shown below to get the adapter to get the
driver to probe without errors, but with these changes, ibping, ib_read_bw,
and ib_write_bw all work both directions:

I think the new coherent flag should probably use a bool instead of int,
even despite the fact that the old one still uses bool.

It might also be worth checking if we need the per-chunk and per-table
coherent flags, or if the per-chunk one is enough.

So we need to store the value in the table, because the table is created first without any chunks, so we can't store the coherent flag in any chunk, and the coherent flag is a property of the table at that time.

We also need to store it per chunk because part of the code acts on chunks without knowledge of which table they're part of, so can't access the per-table coherent flag.

Instead of duplicating the coherent flag into each chunk, I could instead add a pointer from the chunk to the table, so the code could read chunk->table->coherent. That would avoid duplication at least, even if it does add more pointer chasing. I'm not sure if one way is better than the other?

Otherwise this looks fine, feel free to resend it under your name as
you did the original patch and all the analysis and testing.

Thanks.



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