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authorThomas Hellstrom <thellstrom@vmware.com>2014-03-12 10:41:32 +0100
committerThomas Hellstrom <thellstrom@vmware.com>2014-03-12 14:07:24 +0100
commit0e6d6ec02f867fe8d1f785312b7343b21052322f (patch)
treede3e45232186d8eac91b34bf4bd2124a371a9749 /drivers/gpu
parent45db98e54242f3ae94bdcfbfe754e743252eb168 (diff)
drm/ttm: Work around performance regression with VM_PFNMAP
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> Acked-by: Alex Deucher <alexander.deucher@amd.com> Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com> Cc: stable@vger.kernel.org
Diffstat (limited to 'drivers/gpu')
-rw-r--r--drivers/gpu/drm/ttm/ttm_bo_vm.c12
1 files 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 801231c9ae48..0ce48e5a9cb4 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;
}