I think the scatter-gather tables only support system memory. As I understand it, a buffer in VRAM has be migrated to system memory before it can be shared with another driver. I'm more concerned about sharing with the same driver. There is a special code path for that, where we simply add another reference to the same BO, instead of looking at a scatter gather table. We use that for OpenGL-OpenCL interop, and also planning to use it for IPC buffer sharing in HSA. As long as a split VRAM buffer is still a single amdgpu_bo, and becomes a single dmabuf when exporting it, I think that should work. Regards, Felix On 16-08-17 02:58 AM, Christian König wrote: >> One question: Will it be possible to share these split BOs as dmabufs? > In theory yes, in practice I'm not sure. > > DMA-bufs are designed around scatter gather tables, those fortunately > support buffers split over the whole address space. > > The problem is the importing device needs to be able to handle that as > well. > > Regards, > Christian. > > Am 16.08.2016 um 20:33 schrieb Felix Kuehling: >> Very nice. I'm looking forward to this for KFD as well. >> >> One question: Will it be possible to share these split BOs as dmabufs? >> >> Regards, >> Felix >> >> >> On 16-08-16 11:27 AM, Christian König wrote: >>> Hi Marek, >>> >>> I'm already working on this. >>> >>> My current approach is to use a custom BO manager for VRAM with TTM >>> and so split allocations into chunks of 4MB. >>> >>> Large BOs are still swapped out as one, but it makes it much more >>> likely to that you can allocate 1/2 of VRAM as one buffer. >>> >>> Give me till the end of the week to finish this and then we can test >>> if that's sufficient or if we need to do more. >>> >>> Regards, >>> Christian. >>> >>> Am 16.08.2016 um 16:33 schrieb Marek Olšák: >>>> Hi, >>>> >>>> I'm seeing random temporary freezes (up to 2 seconds) under memory >>>> pressure. Before I describe the exact circumstances, I'd like to say >>>> that this is a serious issue affecting playability of certain AAA >>>> Linux games. >>>> >>>> In order to reproduce this, an application should: >>>> - allocate a few very large buffers (256-512 MB per buffer) >>>> - allocate more memory than there is available VRAM. The issue also >>>> occurs (but at a lower frequency) if the app needs only 80% of VRAM. >>>> >>>> Example: ttm_bo_validate needs to migrate a 512 MB buffer. The total >>>> size of moved memory for that call can be as high as 1.5 GB. This is >>>> always followed by a big temporary drop in VRAM usage. >>>> >>>> The game I'm testing needs 3.4 GB of VRAM. >>>> >>>> Setups: >>>> Tonga - 2 GB: It's nearly unplayable, because freezes occur too often. >>>> Fiji - 4 GB: There is one freeze at the beginning (which is annoying >>>> too), after that it's smooth. >>>> >>>> So even 4 GB is not enough. >>>> >>>> Workarounds: >>>> - Split buffers into smaller pieces in the kernel. It's not necessary >>>> to manage memory at page granularity (64KB). Splitting buffers into >>>> 16MB-large pieces might not be optimal but it would be a significant >>>> improvement. >>>> - Or do the same in Mesa. This would prevent inter-process and >>>> inter-API buffer sharing for split buffers (DRI, OpenCL), but we would >>>> at least verify how much the situation improves. >>>> >>>> Other issues sharing the same cause: >>>> - Allocations requesting 1/3 or more VRAM have a high chance of >>>> failing. It's generally not possible to allocate 1/2 or more VRAM as >>>> one buffer. >>>> >>>> Comments welcome, >>>> >>>> Marek >>>> _______________________________________________ >>>> amd-gfx mailing list >>>> amd-gfx at lists.freedesktop.org >>>> https://lists.freedesktop.org/mailman/listinfo/amd-gfx >>> >>> _______________________________________________ >>> amd-gfx mailing list >>> amd-gfx at lists.freedesktop.org >>> https://lists.freedesktop.org/mailman/listinfo/amd-gfx > >
