drm/i915: Keep a small stash of preallocated WC pages
We use WC pages for coherent writes into the ppGTT on !llc
architectures. However, to create a WC page requires a stop_machine(),
i.e. is very slow. To compensate we currently keep a per-vm cache of
recently freed pages, but we still see the slow startup of new contexts.
We can amoritize that cost slightly by allocating WC pages in small
batches (PAGEVEC_SIZE == 14) and since creating a WC page implies a
stop_machine() there is no penalty for keeping that stash global.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20170822173828.5932-1-chris@chris-wilson.co.uk
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 60267e3..7587ef53 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -1465,6 +1465,11 @@ struct i915_gem_mm {
struct llist_head free_list;
struct work_struct free_work;
+ /**
+ * Small stash of WC pages
+ */
+ struct pagevec wc_stash;
+
/** Usable portion of the GTT for GEM */
dma_addr_t stolen_base; /* limited to low memory (32-bit) */