We use WC pages for coherent writes into the ppGTT on !llc
architectuures. 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 <ch...@chris-wilson.co.uk>
---
drivers/gpu/drm/i915/i915_drv.h | 3 ++
drivers/gpu/drm/i915/i915_gem_gtt.c | 82 ++++++++++++++++++++++++++++++-------
2 files changed, 71 insertions(+), 14 deletions(-)
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index d26bc10f488e..e0db2d620170 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -1446,6 +1446,9 @@ 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) */
diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c
b/drivers/gpu/drm/i915/i915_gem_gtt.c
index 10aa7762d9a6..76ca22164a34 100644
--- a/drivers/gpu/drm/i915/i915_gem_gtt.c
+++ b/drivers/gpu/drm/i915/i915_gem_gtt.c
@@ -351,31 +351,77 @@ static gen6_pte_t iris_pte_encode(dma_addr_t addr,
static struct page *vm_alloc_page(struct i915_address_space *vm, gfp_t gfp)
{
- struct page *page;
+ struct pagevec *pvec = &vm->free_pages;
if (I915_SELFTEST_ONLY(should_fail(&vm->fault_attr, 1)))
i915_gem_shrink_all(vm->i915);
- if (vm->free_pages.nr)
- return vm->free_pages.pages[--vm->free_pages.nr];
+ if (likely(pvec->nr))
+ return pvec->pages[--pvec->nr];
- page = alloc_page(gfp);
- if (!page)
+ if (!vm->pt_kmap_wc)
+ return alloc_page(gfp);
+
+ lockdep_assert_held(&vm->i915->drm.struct_mutex);
+
+ /* Look in our global stash of WC pages... */
+ pvec = &vm->i915->mm.wc_stash;
+ if (likely(pvec->nr))
+ return pvec->pages[--pvec->nr];
+
+ /* Otherwise batch allocate pages to amoritize cost of set_pages_wc. */
+ do {
+ struct page *page;
+
+ page = alloc_page(gfp);
+ if (unlikely(!page))
+ break;
+
+ pvec->pages[pvec->nr++] = page;
+ } while (pvec->nr < ARRAY_SIZE(pvec->pages));
+
+ if (unlikely(!pvec->nr))
return NULL;
- if (vm->pt_kmap_wc)
- set_pages_array_wc(&page, 1);
+ set_pages_array_wc(pvec->pages, pvec->nr);
- return page;
+ return pvec->pages[--pvec->nr];
}
-static void vm_free_pages_release(struct i915_address_space *vm)
+static void vm_free_pages_release(struct i915_address_space *vm,
+ bool immediate)
{
GEM_BUG_ON(!pagevec_count(&vm->free_pages));
- if (vm->pt_kmap_wc)
- set_pages_array_wb(vm->free_pages.pages,
- pagevec_count(&vm->free_pages));
+ if (vm->pt_kmap_wc) {
+ struct pagevec *global, *local;
+
+ /* When we use WC, first fill up the global stash and then
+ * only if full immediately free the overflow.
+ */
+
+ lockdep_assert_held(&vm->i915->drm.struct_mutex);
+ global = &vm->i915->mm.wc_stash;
+ local = &vm->free_pages;
+ if (global->nr < ARRAY_SIZE(global->pages)) {
+ do {
+ global->pages[global->nr++] =
+ local->pages[--local->nr];
+ if (!local->nr)
+ return;
+ } while (global->nr < ARRAY_SIZE(global->pages));
+
+ /* As we have made some room in the VM's free_pages,
+ * we can wait for it to fill again. Unless we are
+ * inside i915_address_space_fini() and must
+ * immediately release the pages!
+ */
+ if (!immediate)
+ return;
+ }
+
+ set_pages_array_wb(local->pages, local->nr);
+ }
__pagevec_release(&vm->free_pages);
}
@@ -383,7 +429,7 @@ static void vm_free_pages_release(struct i915_address_space
*vm)
static void vm_free_page(struct i915_address_space *vm, struct page *page)
{
if (!pagevec_add(&vm->free_pages, page))
- vm_free_pages_release(vm);
+ vm_free_pages_release(vm, false);
}
static int __setup_page_dma(struct i915_address_space *vm,
@@ -1867,7 +1913,7 @@ static void i915_address_space_init(struct
i915_address_space *vm,
static void i915_address_space_fini(struct i915_address_space *vm)
{
if (pagevec_count(&vm->free_pages))
- vm_free_pages_release(vm);
+ vm_free_pages_release(vm, true);
i915_gem_timeline_fini(&vm->timeline);
drm_mm_takedown(&vm->mm);
@@ -2593,6 +2639,7 @@ void i915_ggtt_cleanup_hw(struct drm_i915_private
*dev_priv)
{
struct i915_ggtt *ggtt = &dev_priv->ggtt;
struct i915_vma *vma, *vn;
+ struct pagevec *pvec;
ggtt->base.closed = true;
@@ -2616,6 +2663,13 @@ void i915_ggtt_cleanup_hw(struct drm_i915_private
*dev_priv)
}
ggtt->base.cleanup(&ggtt->base);
+
+ pvec = &dev_priv->mm.wc_stash;
+ if (pvec->nr) {
+ set_pages_array_wb(pvec->pages, pvec->nr);
+ __pagevec_release(pvec);
+ }
+
mutex_unlock(&dev_priv->drm.struct_mutex);
arch_phys_wc_del(ggtt->mtrr);
--
2.13.3
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