Messages in this thread | | | Subject | Re: [PATCH] lib/scatterlist: Provide a DMA page iterator | From | Christian König <> | Date | Wed, 16 Jan 2019 11:40:48 +0100 |
| |
Am 15.01.19 um 22:25 schrieb Jason Gunthorpe: > On Tue, Jan 15, 2019 at 02:17:26PM +0000, Thomas Hellstrom wrote: >> Hi, Christoph, >> >> On Mon, 2019-01-14 at 10:48 +0100, Christoph Hellwig wrote: >>> On Thu, Jan 10, 2019 at 04:42:18PM -0700, Jason Gunthorpe wrote: >>>>> Changes since the RFC: >>>>> - Rework vmwgfx too [CH] >>>>> - Use a distinct type for the DMA page iterator [CH] >>>>> - Do not have a #ifdef [CH] >>>> ChristophH: Will you ack? >>> This looks generally fine. >>> >>>> Are you still OK with the vmwgfx reworking, or should we go back to >>>> the original version that didn't have the type safety so this >>>> driver >>>> can be left broken? >>> I think the map method in vmgfx that just does virt_to_phys is >>> pretty broken. Thomas, can you check if you see any performance >>> difference with just doing the proper dma mapping, as that gets the >>> driver out of interface abuse land? >> The performance difference is not really the main problem here. The >> problem is that even though we utilize the streaming DMA interface, we >> use it only since we have to for DMA-Remapping and assume that the >> memory is coherent. To be able to be as compliant as possible and ditch >> the virt-to-phys mode, we *need* a DMA interface flag that tells us >> when the dma_sync_for_xxx are no-ops. If they aren't we'll refuse to >> load for now. I'm not sure, but I think also nouveau and radeon suffer >> from the same issue. > RDMA needs something similar as well, in this case drivers take a > struct page * from get_user_pages() and need to have the DMA map fail > if the platform can't DMA map in a way that does not require any > additional DMA API calls to ensure coherence. (think Userspace RDMA > MR's) > > Today we just do the normal DMA map and when it randomly doesn't work > and corrupts data tell those people their platforms don't support RDMA > - it would be nice to have a safer API base solution..
Oh, yes really good point. We have to support get_user_pages (or HMM) in a similar manner on GPUs as well.
Regards, Christian.
> > Jason > _______________________________________________ > dri-devel mailing list > dri-devel@lists.freedesktop.org > https://lists.freedesktop.org/mailman/listinfo/dri-devel
| |