On Wed, 26 Jul 2017, Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> wrote:
> 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 <chris@xxxxxxxxxxxxxxxxxx>
> ---
> drivers/gpu/drm/i915/i915_drv.h | 3 +
> drivers/gpu/drm/i915/i915_gem_gtt.c | 121 +++++++++++++++++++++++++++++-------
> 2 files changed, 100 insertions(+), 24 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index 2c7456f4ed38..fd62be74a422 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -1464,6 +1464,9 @@ 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 */
These are not proper kernel-doc comments.
BR,
Jani.
> 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..ad4e48435853 100644
> --- a/drivers/gpu/drm/i915/i915_gem_gtt.c
> +++ b/drivers/gpu/drm/i915/i915_gem_gtt.c
> @@ -351,39 +351,85 @@ 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];
> +
> + 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];
>
> - page = alloc_page(gfp);
> - if (!page)
> + /* 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 (pagevec_space(pvec));
> +
> + 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));
> + struct pagevec *pvec = &vm->free_pages;
> +
> + GEM_BUG_ON(!pagevec_count(pvec));
> +
> + if (vm->pt_kmap_wc) {
> + struct pagevec *stash = &vm->i915->mm.wc_stash;
>
> - if (vm->pt_kmap_wc)
> - set_pages_array_wb(vm->free_pages.pages,
> - pagevec_count(&vm->free_pages));
> + /* 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);
> + if (pagevec_space(stash)) {
> + do {
> + stash->pages[stash->nr++] =
> + pvec->pages[--pvec->nr];
> + if (!pvec->nr)
> + return;
> + } while (pagevec_space(stash));
> +
> + /* 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(pvec->pages, pvec->nr);
> + }
>
> - __pagevec_release(&vm->free_pages);
> + __pagevec_release(pvec);
> }
>
> 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,
> @@ -447,12 +493,31 @@ static void fill_page_dma_32(struct i915_address_space *vm,
> static int
> setup_scratch_page(struct i915_address_space *vm, gfp_t gfp)
> {
> - return __setup_page_dma(vm, &vm->scratch_page, gfp | __GFP_ZERO);
> + struct page *page;
> + dma_addr_t addr;
> +
> + page = alloc_page(gfp | __GFP_ZERO);
> + if (unlikely(!page))
> + return -ENOMEM;
> +
> + addr = dma_map_page(vm->dma, page, 0, PAGE_SIZE,
> + PCI_DMA_BIDIRECTIONAL);
> + if (unlikely(dma_mapping_error(vm->dma, addr))) {
> + __free_page(page);
> + return -ENOMEM;
> + }
> +
> + vm->scratch_page.page = page;
> + vm->scratch_page.daddr = addr;
> + return 0;
> }
>
> static void cleanup_scratch_page(struct i915_address_space *vm)
> {
> - cleanup_page_dma(vm, &vm->scratch_page);
> + struct i915_page_dma *p = &vm->scratch_page;
> +
> + dma_unmap_page(vm->dma, p->daddr, PAGE_SIZE, PCI_DMA_BIDIRECTIONAL);
> + __free_page(p->page);
> }
>
> static struct i915_page_table *alloc_pt(struct i915_address_space *vm)
> @@ -1332,18 +1397,18 @@ static int gen8_ppgtt_init(struct i915_hw_ppgtt *ppgtt)
> 1ULL << 48 :
> 1ULL << 32;
>
> - ret = gen8_init_scratch(&ppgtt->base);
> - if (ret) {
> - ppgtt->base.total = 0;
> - return ret;
> - }
> -
> /* There are only few exceptions for gen >=6. chv and bxt.
> * And we are not sure about the latter so play safe for now.
> */
> if (IS_CHERRYVIEW(dev_priv) || IS_BROXTON(dev_priv))
> ppgtt->base.pt_kmap_wc = true;
>
> + ret = gen8_init_scratch(&ppgtt->base);
> + if (ret) {
> + ppgtt->base.total = 0;
> + return ret;
> + }
> +
> if (use_4lvl(vm)) {
> ret = setup_px(&ppgtt->base, &ppgtt->pml4);
> if (ret)
> @@ -1867,7 +1932,7 @@ 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 +2658,7 @@ 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 +2682,13 @@ 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);
--
Jani Nikula, Intel Open Source Technology Center
_______________________________________________
Intel-gfx mailing list
Intel-gfx@xxxxxxxxxxxxxxxxxxxxx
https://lists.freedesktop.org/mailman/listinfo/intel-gfx
