Christian, You misunderstood Alex’s comments,
>Regardless of which scenarios we need to support, I think we also need >to really plumb this through to mesa however since user space is who >ultimately requests the location. Overriding it in the kernel gets >tricky and can lead to ping-ponging as others have noted. Better to Here Alex mentioned the scenarios is 1)VRAM, 2)GTT, 3)VRAM/GTT. His concern is this might cause ping-pong, not about preferred domain. Since preferred domain can solve the ping-pong issue, it shall address his concern here. Regards, Samuel Li From: Christian König [mailto:ckoenig.leichtzumer...@gmail.com] Sent: Monday, March 19, 2018 3:45 PM To: Li, Samuel <samuel...@amd.com>; Marek Olšák <mar...@gmail.com>; Koenig, Christian <christian.koe...@amd.com> Cc: Alex Deucher <alexdeuc...@gmail.com>; Michel Dänzer <mic...@daenzer.net>; amd-gfx list <amd-gfx@lists.freedesktop.org> Subject: Re: [PATCH 1/2] drm/amdgpu: Enable scatter gather display support Quoting Alex: Regardless of which scenarios we need to support, I think we also need to really plumb this through to mesa however since user space is who ultimately requests the location. Overriding it in the kernel gets tricky and can lead to ping-ponging as others have noted. Better to have user space know what chips support it or not and request display buffers in GTT or VRAM from the start. And I completely agree with Alex here. So overriding the domain in the kernel is a serious NAK from my side as well. Please implement the necessary bits in Mesa, shouldn't be more than a few lines of code anyway. Regards, Christian. Am 19.03.2018 um 20:42 schrieb Li, Samuel: Agreed. >I think that the consensus with Alex and me is that we should avoid exactly >that. Christian, Alex’s concern is about ping-pong, not about the preferred domain. Regards, Samuel Li From: Marek Olšák [mailto:mar...@gmail.com] Sent: Monday, March 19, 2018 3:39 PM To: Koenig, Christian <christian.koe...@amd.com><mailto:christian.koe...@amd.com> Cc: Li, Samuel <samuel...@amd.com><mailto:samuel...@amd.com>; Michel Dänzer <mic...@daenzer.net><mailto:mic...@daenzer.net>; Alex Deucher <alexdeuc...@gmail.com><mailto:alexdeuc...@gmail.com>; amd-gfx list <amd-gfx@lists.freedesktop.org><mailto:amd-gfx@lists.freedesktop.org> Subject: Re: [PATCH 1/2] drm/amdgpu: Enable scatter gather display support On Mon, Mar 19, 2018 at 3:27 PM, Christian König <christian.koe...@amd.com<mailto:christian.koe...@amd.com>> wrote: I think that the consensus with Alex and me is that we should avoid exactly that. Overriding the preferred domain in the kernel is a no-go for that patch set, so please implement the discussed changes in Mesa. I don't see how Mesa can make a smarter decision than the kernel. If you overwrite the preferred domain of the buffer in the kernel, there will be no ping-ponging between domains. Mesa never changes the initial preferred domain. Marek Regards, Christian. Am 19.03.2018 um 20:22 schrieb Li, Samuel: I agree with Marek/Michel: since kernel sets the domain before scanning out, it shall update the preferred domain here too. Regards, Samuel Li -----Original Message----- From: Koenig, Christian Sent: Thursday, March 08, 2018 4:07 AM To: Michel Dänzer <mic...@daenzer.net<mailto:mic...@daenzer.net>>; Li, Samuel <samuel...@amd.com<mailto:samuel...@amd.com>>; Alex Deucher <alexdeuc...@gmail.com<mailto:alexdeuc...@gmail.com>> Cc: amd-gfx list <amd-gfx@lists.freedesktop.org<mailto:amd-gfx@lists.freedesktop.org>> Subject: Re: [PATCH 1/2] drm/amdgpu: Enable scatter gather display support Am 08.03.2018 um 09:35 schrieb Michel Dänzer: On 2018-03-07 10:47 AM, Christian König wrote: Am 07.03.2018 um 09:42 schrieb Michel Dänzer: On 2018-03-06 07:23 PM, Christian König wrote: E.g. the last time I tested it placing things into GTT still resulted in quite a performance penalty for rendering. FWIW, I think the penalty is most likely IOMMU related. Last time I tested, I couldn't measure a big difference with IOMMU disabled. No, the penalty I'm talking about came from the ping/pong we did with the scanout buffers. See when I tested this the DDX and Mesa where unmodified, so both still assumed VRAM as placement for scanout BOs, but the kernel forced scanout BOs into GTT for testing. So what happened was that on scanout we moved the VRAM BO to GTT and after unpinning it on the first command submission which used the BO we moved it back to VRAM again. In the meantime, I've had the same idea as Marek: Can't the kernel driver simply change the BO's preferred domain to GTT when scanning out from it? Then it won't move back to VRAM. Yes, I've considered this as well. But I think making the decision in Mesa is the cleaner approach. E.g. so far we only override the placement decision of userspace for two reasons: 1. We where running out of memory in VRAM. 2. We have a hardware restriction which makes VRAM usage mandatory. And even then we never adjust the placement permanently, we just temporary moved the buffer where it was needed and moved it back after the operation completed. Additional to that Mesa might want to set even more flags and/or changes it's behavior. E.g. use a tilling mode which both importer and export in an A+A laptop understands etc... Regards, Christian. _______________________________________________ amd-gfx mailing list amd-gfx@lists.freedesktop.org<mailto:amd-gfx@lists.freedesktop.org> https://lists.freedesktop.org/mailman/listinfo/amd-gfx _______________________________________________ amd-gfx mailing list amd-gfx@lists.freedesktop.org<mailto:amd-gfx@lists.freedesktop.org> https://lists.freedesktop.org/mailman/listinfo/amd-gfx
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