Messages in this thread | | | Date | Tue, 14 Jul 2020 08:36:48 +0200 | From | Greg Kroah-Hartman <> | Subject | Re: [PATCH 1/3] habanalabs: implement dma-fence mechanism |
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On Mon, Jul 13, 2020 at 09:08:55PM +0200, Daniel Vetter wrote: > On Mon, Jul 13, 2020 at 9:03 PM Jason Gunthorpe <jgg@ziepe.ca> wrote: > > > > On Mon, Jul 13, 2020 at 08:34:12PM +0200, Daniel Vetter wrote: > > > On Mon, Jul 13, 2020 at 5:57 PM Greg Kroah-Hartman > > > <gregkh@linuxfoundation.org> wrote: > > > > > > > > On Mon, Jul 13, 2020 at 06:54:22PM +0300, Oded Gabbay wrote: > > > > > From: Ofir Bitton <obitton@habana.ai> > > > > > > > > > > Instead of using standard dma-fence mechanism designed for GPU's, we > > > > > introduce our own implementation based on the former one. This > > > > > implementation is much more sparse than the original, contains only > > > > > mandatory functionality required by the driver. > > > > > > > > Sad you can't use the in-kernel code for this, I really don't understand > > > > what's wrong with using it as-is. > > > > > > > > Daniel, why do we need/want duplicate code floating around in the tree > > > > like this? > > > > > > The rules around dma-fence are ridiculously strict, and it only makes > > > sense to inflict that upon you if you actually want to participate in > > > the cross driver uapi built up around dma-buf and dma-fence. > > > > > > I've recently started some lockdep annotations to better enforce these > > > rules (and document them), and it's finding tons of subtle bugs even > > > in drivers/gpu (and I only just started with annotating drivers: > > > > > > https://lore.kernel.org/dri-devel/20200707201229.472834-1-daniel.vetter@ffwll.ch/ > > > > > > You really don't want to deal with this if you don't have to. If > > > drivers/gpu folks (who created this) aren't good enough to understand > > > it, maybe it's not a good idea to sprinkle this all over the tree. And > > > fundamentally all this is is a slightly fancier struct completion. Use > > > that one instead, or a wait_queue. > > > > > > I discussed this a bit with Oded, and he thinks it's easier to > > > copypaste and simplify, but given that all other drivers seem to get > > > by perfectly well with completion or wait_queue, I'm not sure that's a > > > solid case. > > > > > > Also adding Jason Gunthorpe, who very much suggested this should be > > > limited to dma-buf/gpu related usage only. > > > > Without all the cross-driver stuff dma_fence is just a > > completion. Using dma_fence to get a completion is big abuse of what > > it is intended for. > > > > I think the only problem with this patch is that it keeps too much of > > the dma_fence stuff around. From what I could tell it really just > > wants to add a kref and completion to struct hl_cs_compl and delete > > everything to do with dma_fence. > > Yeah, that's what I recommended doing too. error flag might be needed > too I think, but that's it.
Ok, so this should be made much simpler and not use this copy/paste code at all. I can accept that :)
Ofir, care to redo this?
thanks,
greg k-h
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