On Wed, Aug 07, 2019 at 06:57:24AM +0000, Koenig, Christian wrote: > Am 06.08.19 um 22:03 schrieb Jason Gunthorpe: > > On Tue, Aug 06, 2019 at 02:58:58PM -0400, Alex Deucher wrote: > >> On Tue, Aug 6, 2019 at 1:51 PM Kuehling, Felix <Felix.Kuehling@xxxxxxx> wrote: > >>> On 2019-08-06 13:44, Jason Gunthorpe wrote: > >>>> On Tue, Aug 06, 2019 at 07:05:53PM +0300, Christoph Hellwig wrote: > >>>>> The option is just used to select HMM mirror support and has a very > >>>>> confusing help text. Just pull in the HMM mirror code by default > >>>>> instead. > >>>>> > >>>>> Signed-off-by: Christoph Hellwig <hch@xxxxxx> > >>>>> drivers/gpu/drm/Kconfig | 2 ++ > >>>>> drivers/gpu/drm/amd/amdgpu/Kconfig | 10 ---------- > >>>>> drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c | 6 ------ > >>>>> drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.h | 12 ------------ > >>>>> 4 files changed, 2 insertions(+), 28 deletions(-) > >>>> Felix, was this an effort to avoid the arch restriction on hmm or > >>>> something? Also can't see why this was like this. > >>> This option predates KFD's support of userptrs, which in turn predates > >>> HMM. Radeon has the same kind of option, though it doesn't affect HMM in > >>> that case. > >>> > >>> Alex, Christian, can you think of a good reason to maintain userptr > >>> support as an option in amdgpu? I suspect it was originally meant as a > >>> way to allow kernels with amdgpu without MMU notifiers. Now it would > >>> allow a kernel with amdgpu without HMM or MMU notifiers. I don't know if > >>> this is a useful thing to have. > >> Right. There were people that didn't have MMU notifiers that wanted > >> support for the GPU. > > ?? Is that even a real thing? mmu_notifier does not have much kconfig > > dependency. > > Yes, that used to be a very real thing. > > Initially a lot of users didn't wanted mmu notifiers to be enabled > because of the performance overhead they costs. Seems strange to hear these days, every distro ships with it on, it is needed for kvm. > Then we had the problem that HMM mirror wasn't available on a lot of > architectures. Some patches for hmm are ready now that will fix this Jason
