On Mon, Feb 8, 2021 at 9:51 PM John Stultz john.stultz@linaro.org wrote:
On Mon, Feb 8, 2021 at 2:08 AM Daniel Vetter daniel@ffwll.ch wrote:
On Sat, Feb 06, 2021 at 05:47:48AM +0000, John Stultz wrote:
By default dma_buf_export() sets the exporter name to be KBUILD_MODNAME. Unfortunately this may not be identical to the string used as the heap name (ie: "system" vs "system_heap").
This can cause some minor confusion with tooling, and there is the future potential where multiple heap types may be exported by the same module (but would all have the same name).
So to avoid all this, set the exporter exp_name to the heap name.
Cc: Daniel Vetter daniel@ffwll.ch Cc: Sumit Semwal sumit.semwal@linaro.org Cc: Liam Mark lmark@codeaurora.org Cc: Chris Goldsworthy cgoldswo@codeaurora.org Cc: Laura Abbott labbott@kernel.org Cc: Brian Starkey Brian.Starkey@arm.com Cc: Hridya Valsaraju hridya@google.com Cc: Suren Baghdasaryan surenb@google.com Cc: Sandeep Patil sspatil@google.com Cc: Daniel Mentz danielmentz@google.com Cc: Ørjan Eide orjan.eide@arm.com Cc: Robin Murphy robin.murphy@arm.com Cc: Ezequiel Garcia ezequiel@collabora.com Cc: Simon Ser contact@emersion.fr Cc: James Jones jajones@nvidia.com Cc: linux-media@vger.kernel.org Cc: dri-devel@lists.freedesktop.org Signed-off-by: John Stultz john.stultz@linaro.org
Looks reasonable to me.
I guess the main worry is "does this mean heap names become uapi", in which case I'm maybe not so sure anymore how this will tie into the overall gpu memory accounting story.
Since for dma-buf heaps one name per buffer is perfectly fine, since dma-buf heaps aren't very dynamic. But on discrete gpu drivers buffers move, so baking in the assumption that "exporter name = resource usage for this buffer" is broken.
I suspect I'm missing a subtlety in what you're describing. My sense of the exporter name doesn't account for a buffer's usage, it just describes what code allocated it and implicitly which dmabuf_ops handles it. Maybe could you give a more specific example of what you're hoping to avoid?
Just paranoia really - on the linux side where we allocate most buffers (even shared ones) with the driver, that allocator info isn't that meaningful, it really just tells you which code allocated/exported that dma-buf.
But on Android, where all shared buffers come from specific heaps, it is rather meaningful information. So I wondered whether e.g. the android dmabuf debug tool uses that to collect per-heap stats, but sounds like no right now. Plus with the chat we've had I think we have a long-term plan for how to expose that information properly.
To me this patch is mostly just a consistency/least-surprise thing, so the heaps exporter name matches the string used for the heap's chardev device (the interface used to allocate it) in output like debugfs/dma_buf/bufinfo.
Yeah for debug this makes sense. a-b: me if you want that somewhere on the patches. -Daniel