From: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
To: Jason Gunthorpe <jgg@nvidia.com>
Cc: Maor Gottlieb <maorg@nvidia.com>, Christoph Hellwig <hch@lst.de>,
Gal Pressman <galpress@amazon.com>,
Bob Pearson <rpearsonhpe@gmail.com>,
Leon Romanovsky <leonro@nvidia.com>,
linux-rdma@vger.kernel.org
Subject: Re: dynamic-sg patch has broken rdma_rxe
Date: Tue, 20 Oct 2020 13:31:27 +0100 [thread overview]
Message-ID: <c64bc07a-ed95-f462-a394-4191605c05b9@linux.intel.com> (raw)
In-Reply-To: <20201020114710.GC6219@nvidia.com>
On 20/10/2020 12:47, Jason Gunthorpe wrote:
> On Tue, Oct 20, 2020 at 12:37:05PM +0100, Tvrtko Ursulin wrote:
>
>>> Why put this confusing code in every caller? Especially for something
>>> a driver is supposed to call. Will just make bugs
>>
>> For max_segment to be aligned is a requirement today so callers are
>> ready.
>
> No, it turns out all the RDMA drivers were became broken when they
> converted to use the proper U32_MAX for their DMA max_segment size,
> then they couldn't form SGLs anymore.
>
> I don't want to see nonsense code like this:
>
> dma_set_max_seg_size(dev->dev, min_t(unsigned int, U32_MAX & PAGE_MASK,
> SCATTERLIST_MAX_SEGMENT));
>
> In drivers.
>
> dma_set_max_seg_size is the *hardware* capability, and mixing in
> things like PAG_MASK here is just nonsense.
Code was obviously a no-op non-sense.
So the crux of the argument is that U32_MAX is conceptually the right
thing which defines the DMA max_segment size? Not some DMA define or
anything, but really U32_MAX? And that all/some DMA hardware does not
think in pages but really in bytes?
Regards,
Tvrtko
next prev parent reply other threads:[~2020-10-20 12:31 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-13 14:33 dynamic-sg patch has broken rdma_rxe Bob Pearson
2020-10-13 16:34 ` Bob Pearson
2020-10-14 22:51 ` Jason Gunthorpe
2020-10-15 7:44 ` Maor Gottlieb
2020-10-15 11:23 ` Gal Pressman
2020-10-15 12:21 ` Maor Gottlieb
2020-10-16 0:31 ` Jason Gunthorpe
2020-10-16 7:13 ` Christoph Hellwig
[not found] ` <796ca31aed8f469c957cb850385b9d09@intel.com>
2020-10-16 11:58 ` Jason Gunthorpe
2020-10-19 9:50 ` Tvrtko Ursulin
2020-10-19 12:12 ` Jason Gunthorpe
2020-10-19 12:29 ` Tvrtko Ursulin
2020-10-19 12:48 ` Jason Gunthorpe
2020-10-20 11:37 ` Tvrtko Ursulin
2020-10-20 11:47 ` Jason Gunthorpe
2020-10-20 12:31 ` Tvrtko Ursulin [this message]
2020-10-20 12:56 ` Jason Gunthorpe
2020-10-20 13:09 ` Tvrtko Ursulin
2020-10-20 13:32 ` Jason Gunthorpe
2020-10-15 15:35 ` Bob Pearson
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