• Chris Wilson's avatar
    drm/i915: Fix i915_gem_evict_for_vma (soft-pinning) · 172ae5b4
    Chris Wilson authored
    Soft-pinning depends upon being able to check for availabilty of an
    interval and evict overlapping object from a drm_mm range manager very
    quickly. Currently it uses a linear list, and so performance is dire and
    not suitable as a general replacement. Worse, the current code will oops
    if it tries to evict an active buffer.
    
    It also helps if the routine reports the correct error codes as expected
    by its callers and emits a tracepoint upon use.
    
    For posterity since the wrong patch was pushed (i.e. that missed these
    key points and had known bugs), this is the changelog that should have
    been on commit 506a8e87 ("drm/i915: Add soft-pinning API for
    execbuffer"):
    
    Userspace can pass in an offset that it presumes the object is located
    at. The kernel will then do its utmost to fit the object into that
    location. The assumption is that userspace is handling its own object
    locations (for example along with full-ppgtt) and that the kernel will
    rarely have to make space for the user's requests.
    
    This extends the DRM_IOCTL_I915_GEM_EXECBUFFER2 to do the following:
    * if the user supplies a virtual address via the execobject->offset
      *and* sets the EXEC_OBJECT_PINNED flag in execobject->flags, then
      that object is placed at that offset in the address space selected
      by the context specifier in execbuffer.
    * the location must be aligned to the GTT page size, 4096 bytes
    * as the object is placed exactly as specified, it may be used by this
      execbuffer call without relocations pointing to it
    
    It may fail to do so if:
    * EINVAL is returned if the object does not have a 4096 byte aligned
      address
    * the object conflicts with another pinned object (either pinned by
      hardware in that address space, e.g. scanouts in the aliasing ppgtt)
      or within the same batch.
      EBUSY is returned if the location is pinned by hardware
      EINVAL is returned if the location is already in use by the batch
    * EINVAL is returned if the object conflicts with its own alignment (as meets
      the hardware requirements) or if the placement of the object does not fit
      within the address space
    
    All other execbuffer errors apply.
    
    Presence of this execbuf extension may be queried by passing
    I915_PARAM_HAS_EXEC_SOFTPIN to DRM_IOCTL_I915_GETPARAM and checking for
    a reported value of 1 (or greater).
    
    v2: Combine the hole/adjusted-hole ENOSPC checks
    v3: More color, more splitting, more blurb.
    
    Fixes: 506a8e87 ("drm/i915: Add soft-pinning API for execbuffer")
    Signed-off-by: default avatarChris Wilson <chris@chris-wilson.co.uk>
    Reviewed-by: default avatarJoonas Lahtinen <joonas.lahtinen@linux.intel.com>
    Link: http://patchwork.freedesktop.org/patch/msgid/20161205142941.21965-2-chris@chris-wilson.co.uk
    172ae5b4
i915_gem_evict.c 10.6 KB