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| author | Thomas Hellstrom <thellstrom@vmware.com> | 2014-03-12 09:41:32 (GMT) |
|---|---|---|
| committer | Thomas Hellstrom <thellstrom@vmware.com> | 2014-03-12 13:07:24 (GMT) |
| commit | 0e6d6ec02f867fe8d1f785312b7343b21052322f (patch) | |
| tree | de3e45232186d8eac91b34bf4bd2124a371a9749 | |
| parent | 45db98e54242f3ae94bdcfbfe754e743252eb168 (diff) | |
| download | linux-0e6d6ec02f867fe8d1f785312b7343b21052322f.tar.xz | |
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
| -rw-r--r-- | drivers/gpu/drm/ttm/ttm_bo_vm.c | 12 |
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 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; } |