s/not/now/. I meant to say, "we have NOW excluded the possibility of ever setting displays anywhere else without a kernel update".
Alex From: amd-gfx [mailto:[email protected]] On Behalf Of Deucher, Alexander Sent: Monday, March 19, 2018 4:13 PM To: Li, Samuel <[email protected]>; Koenig, Christian <[email protected]>; Marek Olšák <[email protected]> Cc: Alex Deucher <[email protected]>; Michel Dänzer <[email protected]>; amd-gfx list <[email protected]> Subject: Re: [PATCH 1/2] drm/amdgpu: Enable scatter gather display support I'm not sure what you mean by the 3 scenarios. Generally userspace selects what domains it wants a buffer to be in, vram, gtt, or both (don't care). I'd rather not have the kernel second guess the UMDs if we can help it. I'd rather leave the kernel for cases where we have to force things due to hw bugs, or hw restrictions, etc. If we force all display buffers to be in gtt in the kernel, we have not excluded the possibility of ever setting displays anywhere else without a kernel update. E.g., to my earlier point, there may be cases where it is advantageous to put display buffers in vram even if s/g display is supported. That was the point I was trying to make about user mode selecting the domain (vram of gtt or vram|gtt). Say you have a board with 2 GB of ram and 1 GB is carved out for "vram". In that case, it would make sense to put the buffer in vram because otherwise you are wasting a comparatively scarce resource. Alex ________________________________ From: Li, Samuel Sent: Monday, March 19, 2018 3:58:52 PM To: Deucher, Alexander; Koenig, Christian; Marek Olšák Cc: Alex Deucher; Michel Dänzer; amd-gfx list Subject: RE: [PATCH 1/2] drm/amdgpu: Enable scatter gather display support Alex, I assume you are talking the three scenarios here, 1)VRAM, 2)GTT, 3)VRAM/GTT. But kernel will need the decision too(amdgpufb). I think it shall be better to do it in kernel, instead of different clients(mesa, ddx, kernel ...) Regards, Samuel Li From: Deucher, Alexander Sent: Monday, March 19, 2018 3:54 PM To: Li, Samuel <[email protected]>; Koenig, Christian <[email protected]>; Marek Olšák <[email protected]> Cc: Alex Deucher <[email protected]>; Michel Dänzer <[email protected]>; amd-gfx list <[email protected]> Subject: Re: [PATCH 1/2] drm/amdgpu: Enable scatter gather display support My personal preference is still to plumb this through to mesa rather than forcing it in the kernel. Alex ________________________________ From: amd-gfx <[email protected]<mailto:[email protected]>> on behalf of Li, Samuel <[email protected]<mailto:[email protected]>> Sent: Monday, March 19, 2018 3:50:34 PM To: Koenig, Christian; Marek Olšák Cc: Alex Deucher; Michel Dänzer; amd-gfx list Subject: RE: [PATCH 1/2] drm/amdgpu: Enable scatter gather display support 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:[email protected]] Sent: Monday, March 19, 2018 3:45 PM To: Li, Samuel <[email protected]<mailto:[email protected]>>; Marek Olšák <[email protected]<mailto:[email protected]>>; Koenig, Christian <[email protected]<mailto:[email protected]>> Cc: Alex Deucher <[email protected]<mailto:[email protected]>>; Michel Dänzer <[email protected]<mailto:[email protected]>>; amd-gfx list <[email protected]<mailto:[email protected]>> 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:[email protected]] Sent: Monday, March 19, 2018 3:39 PM To: Koenig, Christian <[email protected]><mailto:[email protected]> Cc: Li, Samuel <[email protected]><mailto:[email protected]>; Michel Dänzer <[email protected]><mailto:[email protected]>; Alex Deucher <[email protected]><mailto:[email protected]>; amd-gfx list <[email protected]><mailto:[email protected]> Subject: Re: [PATCH 1/2] drm/amdgpu: Enable scatter gather display support On Mon, Mar 19, 2018 at 3:27 PM, Christian König <[email protected]<mailto:[email protected]>> 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 <[email protected]<mailto:[email protected]>>; Li, Samuel <[email protected]<mailto:[email protected]>>; Alex Deucher <[email protected]<mailto:[email protected]>> Cc: amd-gfx list <[email protected]<mailto:[email protected]>> 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 [email protected]<mailto:[email protected]> https://lists.freedesktop.org/mailman/listinfo/amd-gfx _______________________________________________ amd-gfx mailing list [email protected]<mailto:[email protected]> https://lists.freedesktop.org/mailman/listinfo/amd-gfx
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