On Wed, Mar 12, 2014 at 8:12 AM, Thomas Hellstrom thellstrom@vmware.com 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@gmail.com Signed-off-by: Thomas Hellstrom thellstrom@vmware.com Cc: stable@vger.kernel.org
Acked-by: Alex Deucher alexander.deucher@amd.com
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;}
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