Right now, validating a buffer object forces every missing page to be allocated. That means for things like vertex buffer objects, we either need to create them at the 'right' size, or pay a significant penalty when a large buffer is mapped to the card.
It seems like it should be far better to just use a page full of zeros
in the read-only case.
Here's a patch which does that, however I cannot test it as Mesa never
asks for read-only kernel-allocated pages. I'm hoping that can be fixed;
it means knowing up-front whether a buffer will ever be used as a
rendering target, or fixing the API so the validate call knows the
intended GPU access. The latter is probably more reasonable, so perhaps
I'll explore that. Suggestions, as always, are welcome.
commit 864298592f60bcfadeb35e33e1789025d0f19b0b
Author: Keith Packard <[EMAIL PROTECTED]>
Date: Sun Dec 16 01:47:51 2007 -0800
Use dummy_read_page for unpopulated kernel-allocated ttm pages.
Previously, dummy_read_page was used only for read-only user allocations; it
filled in pages that were not present in the user address map (presumably,
these were allocated but never written to pages).
This patch allows them to be used for read-only ttms allocated from the
kernel, so that applications can over-allocate buffers without forcing every
page to be allocated.
diff --git a/linux-core/drm_agpsupport.c b/linux-core/drm_agpsupport.c
index e8bfaea..0218701 100644
--- a/linux-core/drm_agpsupport.c
+++ b/linux-core/drm_agpsupport.c
@@ -505,12 +505,14 @@ static int drm_agp_needs_unbind_cache_adjust(struct
drm_ttm_backend *backend)
static int drm_agp_populate(struct drm_ttm_backend *backend,
- unsigned long num_pages, struct page **pages)
+ unsigned long num_pages, struct page **pages,
+ struct page *dummy_read_page)
{
struct drm_agp_ttm_backend *agp_be =
container_of(backend, struct drm_agp_ttm_backend, backend);
struct page **cur_page, **last_page = pages + num_pages;
DRM_AGP_MEM *mem;
+ int dummy_page_count = 0;
if (drm_alloc_memctl(num_pages * sizeof(void *)))
return -1;
@@ -528,8 +530,16 @@ static int drm_agp_populate(struct drm_ttm_backend
*backend,
DRM_DEBUG("Current page count is %ld\n", (long) mem->page_count);
mem->page_count = 0;
- for (cur_page = pages; cur_page < last_page; ++cur_page)
- mem->memory[mem->page_count++] =
phys_to_gart(page_to_phys(*cur_page));
+ for (cur_page = pages; cur_page < last_page; ++cur_page) {
+ struct page *page = *cur_page;
+ if (!page) {
+ page = dummy_read_page;
+ ++dummy_page_count;
+ }
+ mem->memory[mem->page_count++] =
phys_to_gart(page_to_phys(page));
+ }
+ if (dummy_page_count)
+ DRM_DEBUG("Mapped %d dummy pages\n", dummy_page_count);
agp_be->mem = mem;
return 0;
}
diff --git a/linux-core/drm_objects.h b/linux-core/drm_objects.h
index 375420d..47b6b01 100644
--- a/linux-core/drm_objects.h
+++ b/linux-core/drm_objects.h
@@ -263,7 +263,8 @@ struct drm_ttm_backend;
struct drm_ttm_backend_func {
int (*needs_ub_cache_adjust) (struct drm_ttm_backend *backend);
int (*populate) (struct drm_ttm_backend *backend,
- unsigned long num_pages, struct page **pages);
+ unsigned long num_pages, struct page **pages,
+ struct page *dummy_read_page);
void (*clear) (struct drm_ttm_backend *backend);
int (*bind) (struct drm_ttm_backend *backend,
struct drm_bo_mem_reg *bo_mem);
diff --git a/linux-core/drm_ttm.c b/linux-core/drm_ttm.c
index c1fc13f..a9d8733 100644
--- a/linux-core/drm_ttm.c
+++ b/linux-core/drm_ttm.c
@@ -262,7 +262,6 @@ int drm_ttm_set_user(struct drm_ttm *ttm,
{
struct mm_struct *mm = tsk->mm;
int ret;
- int i;
int write = (ttm->page_flags & DRM_TTM_PAGE_WRITE) != 0;
BUG_ON(num_pages != ttm->num_pages);
@@ -278,11 +277,6 @@ int drm_ttm_set_user(struct drm_ttm *ttm,
return -ENOMEM;
}
- for (i = 0; i < num_pages; ++i) {
- if (ttm->pages[i] == NULL)
- ttm->pages[i] = ttm->dummy_read_page;
- }
-
return 0;
}
@@ -304,12 +298,14 @@ int drm_ttm_populate(struct drm_ttm *ttm)
return 0;
be = ttm->be;
- for (i = 0; i < ttm->num_pages; ++i) {
- page = drm_ttm_get_page(ttm, i);
- if (!page)
- return -ENOMEM;
+ if (ttm->page_flags & DRM_TTM_PAGE_WRITE) {
+ for (i = 0; i < ttm->num_pages; ++i) {
+ page = drm_ttm_get_page(ttm, i);
+ if (!page)
+ return -ENOMEM;
+ }
}
- be->func->populate(be, ttm->num_pages, ttm->pages);
+ be->func->populate(be, ttm->num_pages, ttm->pages,
ttm->dummy_read_page);
ttm->state = ttm_unbound;
return 0;
}
diff --git a/linux-core/nouveau_sgdma.c b/linux-core/nouveau_sgdma.c
index f3bf534..6c61819 100644
--- a/linux-core/nouveau_sgdma.c
+++ b/linux-core/nouveau_sgdma.c
@@ -25,7 +25,7 @@ nouveau_sgdma_needs_ub_cache_adjust(struct drm_ttm_backend
*be)
static int
nouveau_sgdma_populate(struct drm_ttm_backend *be, unsigned long num_pages,
- struct page **pages)
+ struct page **pages, struct page *dummy_read_page)
{
struct nouveau_sgdma_be *nvbe = (struct nouveau_sgdma_be *)be;
int p, d, o;
@@ -41,8 +41,11 @@ nouveau_sgdma_populate(struct drm_ttm_backend *be, unsigned
long num_pages,
nvbe->pages_populated = d = 0;
for (p = 0; p < num_pages; p++) {
for (o = 0; o < PAGE_SIZE; o += NV_CTXDMA_PAGE_SIZE) {
+ struct page *page = pages[p];
+ if (!page)
+ page = dummy_read_page;
nvbe->pagelist[d] = pci_map_page(nvbe->dev->pdev,
- pages[p], o,
+ page, o,
NV_CTXDMA_PAGE_SIZE,
PCI_DMA_BIDIRECTIONAL);
if (pci_dma_mapping_error(nvbe->pagelist[d])) {
@@ -299,7 +302,7 @@ nouveau_sgdma_nottm_hack_init(struct drm_device *dev)
}
dev_priv->gart_info.sg_handle = sgreq.handle;
- if ((ret = be->func->populate(be, dev->sg->pages, dev->sg->pagelist))) {
+ if ((ret = be->func->populate(be, dev->sg->pages, dev->sg->pagelist,
dev->bm.dummy_read_page))) {
DRM_ERROR("failed populate: %d\n", ret);
return ret;
}
--
[EMAIL PROTECTED]
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