On Wed, Mar 12, 2014 at 8:12 AM, Thomas Hellstrom <thellstrom@xxxxxxxxxx> wrote: > A performance regression was introduced in TTM in linux 3.13 when we started using > VM_PFNMAP for shared mappings. In theory this should've been faster due to > less page book-keeping but it appears like VM_PFNMAP + x86 PAT + write-combine > is a particularly cpu-hungry combination, as seen by largely increased > cpu-usage on r200 GL video playback. > > Until we've sorted out why, revert to always use VM_MIXEDMAP. > Reference: freedesktop.org bugzilla bug #75719 > > Reported-and-tested-by: <smoki00790@xxxxxxxxx> > Signed-off-by: Thomas Hellstrom <thellstrom@xxxxxxxxxx> > Cc: stable@xxxxxxxxxxxxxxx Acked-by: Alex Deucher <alexander.deucher@xxxxxxx> > --- > drivers/gpu/drm/ttm/ttm_bo_vm.c | 12 +++++++----- > 1 file changed, 7 insertions(+), 5 deletions(-) > > diff --git a/drivers/gpu/drm/ttm/ttm_bo_vm.c b/drivers/gpu/drm/ttm/ttm_bo_vm.c > index 801231c..0ce48e5 100644 > --- a/drivers/gpu/drm/ttm/ttm_bo_vm.c > +++ b/drivers/gpu/drm/ttm/ttm_bo_vm.c > @@ -339,11 +339,13 @@ int ttm_bo_mmap(struct file *filp, struct vm_area_struct *vma, > vma->vm_private_data = bo; > > /* > - * PFNMAP is faster than MIXEDMAP due to reduced page > - * administration. So use MIXEDMAP only if private VMA, where > - * we need to support COW. > + * We'd like to use VM_PFNMAP on shared mappings, where > + * (vma->vm_flags & VM_SHARED) != 0, for performance reasons, > + * but for some reason VM_PFNMAP + x86 PAT + write-combine is very > + * bad for performance. Until that has been sorted out, use > + * VM_MIXEDMAP on all mappings. See freedesktop.org bug #75719 > */ > - vma->vm_flags |= (vma->vm_flags & VM_SHARED) ? VM_PFNMAP : VM_MIXEDMAP; > + vma->vm_flags |= VM_MIXEDMAP; > vma->vm_flags |= VM_IO | VM_DONTEXPAND | VM_DONTDUMP; > return 0; > out_unref: > @@ -359,7 +361,7 @@ int ttm_fbdev_mmap(struct vm_area_struct *vma, struct ttm_buffer_object *bo) > > vma->vm_ops = &ttm_bo_vm_ops; > vma->vm_private_data = ttm_bo_reference(bo); > - vma->vm_flags |= (vma->vm_flags & VM_SHARED) ? VM_PFNMAP : VM_MIXEDMAP; > + vma->vm_flags |= VM_MIXEDMAP; > vma->vm_flags |= VM_IO | VM_DONTEXPAND; > return 0; > } > -- > 1.7.10.4 > _______________________________________________ > dri-devel mailing list > dri-devel@xxxxxxxxxxxxxxxxxxxxx > http://lists.freedesktop.org/mailman/listinfo/dri-devel _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/dri-devel
