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 <michel at daenzer.net>; Li, Samuel > <Samuel.Li at amd.com>; Alex Deucher <alexdeucher at gmail.com> > Cc: amd-gfx list <amd-gfx at 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.
