| Message ID | 20170512174909.1063-1-chris@chris-wilson.co.uk (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Fri, May 12, 2017 at 06:49:09PM +0100, Chris Wilson wrote: > We have always excluded the top-page of the Global GTT to prevent > prefetching past the end of the address space. We have been lax about > applying this restriction to the per-process GTT, but there is no reason > to believe that the hw restriction is any less severe. Other than empirical, but the note in bspec is still there and who knows they may start to be strict again in future. -Chris
On 12 May 2017 at 18:49, Chris Wilson <chris@chris-wilson.co.uk> wrote: > We have always excluded the top-page of the Global GTT to prevent > prefetching past the end of the address space. We have been lax about > applying this restriction to the per-process GTT, but there is no reason > to believe that the hw restriction is any less severe. > > Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Matthew Auld <matthew.auld@intel.com>
On Fri, May 12, 2017 at 06:55:35PM +0100, Chris Wilson wrote: > On Fri, May 12, 2017 at 06:49:09PM +0100, Chris Wilson wrote: > > We have always excluded the top-page of the Global GTT to prevent > > prefetching past the end of the address space. We have been lax about > > applying this restriction to the per-process GTT, but there is no reason > > to believe that the hw restriction is any less severe. > > Other than empirical, but the note in bspec is still there and who knows > they may start to be strict again in future. Fwiw, it looks like we can sleep on this again. Jason no longer believes this to be an immediate issue. -Chris
On 12/05/17 12:06, Chris Wilson wrote: > On Fri, May 12, 2017 at 06:55:35PM +0100, Chris Wilson wrote: >> On Fri, May 12, 2017 at 06:49:09PM +0100, Chris Wilson wrote: >>> We have always excluded the top-page of the Global GTT to prevent >>> prefetching past the end of the address space. We have been lax about >>> applying this restriction to the per-process GTT, but there is no reason >>> to believe that the hw restriction is any less severe. >> >> Other than empirical, but the note in bspec is still there and who knows >> they may start to be strict again in future. > > Fwiw, it looks like we can sleep on this again. Jason no longer believes > this to be an immediate issue. > -Chris > It might be true for 32b ppgtt, but anything slightly recent should already be using 48b. -Michel
diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c b/drivers/gpu/drm/i915/i915_gem_gtt.c index 5332d8cb1c53..f18ca11a8da6 100644 --- a/drivers/gpu/drm/i915/i915_gem_gtt.c +++ b/drivers/gpu/drm/i915/i915_gem_gtt.c @@ -1860,7 +1860,8 @@ static void i915_address_space_init(struct i915_address_space *vm, { i915_gem_timeline_init(dev_priv, &vm->timeline, name); - drm_mm_init(&vm->mm, 0, vm->total); + /* Always exclude the top page to avoid prefetches past the end. */ + drm_mm_init(&vm->mm, 0, vm->total - I915_GTT_PAGE_SIZE); vm->mm.head_node.color = I915_COLOR_UNEVICTABLE; INIT_LIST_HEAD(&vm->active_list); @@ -2390,7 +2391,7 @@ static void i915_gtt_color_adjust(const struct drm_mm_node *node, * GTT boundary. */ node = list_next_entry(node, node_list); - if (node->color != color) + if (node->allocated && node->color != color) *end -= I915_GTT_PAGE_SIZE; }
We have always excluded the top-page of the Global GTT to prevent prefetching past the end of the address space. We have been lax about applying this restriction to the per-process GTT, but there is no reason to believe that the hw restriction is any less severe. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> --- drivers/gpu/drm/i915/i915_gem_gtt.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)