Re: [PATCH 3/6] drm: add unified vma offset manager

On Mon, Jul 01, 2013 at 08:33:00PM +0200, David Herrmann wrote:

If we want to map GPU memory into user-space, we need to linearize the addresses to not confuse mm-core. Currently, GEM and TTM both implement their own offset-managers to assign a pgoff to each object for user-space CPU access. GEM uses a hash-table, TTM uses an rbtree.

This patch provides a unified implementation that can be used to replace both. TTM allows partial mmaps with a given offset, so we cannot use hashtables as the start address may not be known at mmap time. Hence, we use the rbtree-implementation of TTM.

We could easily update drm_mm to use an rbtree instead of a linked list for it's object list and thus drop the rbtree from the vma-manager. However, this would slow down drm_mm object allocation for all other use-cases (rbtree insertion) and add another 4-8 bytes to each mm node. Hence, use the separate tree but allow for later migration.

This is a rewrite of the 2012-proposal by David Airlie airlied@linux.ie

Signed-off-by: David Herrmann dh.herrmann@gmail.com

This seems to sprinkle a lot of likely/unlikely. Imo those are only justified in two cases: - When we have real performance data proving that they're worth it. - Sometimes they're also useful as self-documenting code for the truly unlikely. But early do-nothing returns and error handling are established code patterns, so imo don't qualify.

I think none of the likely/unlikely below qualify, so imo better to remove them.

Second high-level review request: Can you please convert the very nice documentation you already added into proper kerneldoc and link it up at an appropriate section in the drm DocBook?

A few more comments below. I'll postpone reviewing the gem/ttm conversion patches until this is settled a bit.

---

drivers/gpu/drm/Makefile | 2 +- drivers/gpu/drm/drm_vma_manager.c | 224 ++++++++++++++++++++++++++++++++++++++ include/drm/drm_vma_manager.h | 107 ++++++++++++++++++ 3 files changed, 332 insertions(+), 1 deletion(-) create mode 100644 drivers/gpu/drm/drm_vma_manager.c create mode 100644 include/drm/drm_vma_manager.h

diff --git a/drivers/gpu/drm/Makefile b/drivers/gpu/drm/Makefile index 1c9f2439..f8851cc 100644 --- a/drivers/gpu/drm/Makefile +++ b/drivers/gpu/drm/Makefile @@ -12,7 +12,7 @@ drm-y := drm_auth.o drm_buffer.o drm_bufs.o drm_cache.o \ drm_platform.o drm_sysfs.o drm_hashtab.o drm_mm.o \ drm_crtc.o drm_modes.o drm_edid.o \ drm_info.o drm_debugfs.o drm_encoder_slave.o \

• drm_trace_points.o drm_global.o drm_prime.o
  

• drm_trace_points.o drm_global.o drm_prime.o drm_vma_manager.o
  
  

drm-$(CONFIG_COMPAT) += drm_ioc32.o drm-$(CONFIG_DRM_GEM_CMA_HELPER) += drm_gem_cma_helper.o diff --git a/drivers/gpu/drm/drm_vma_manager.c b/drivers/gpu/drm/drm_vma_manager.c new file mode 100644 index 0000000..c28639f --- /dev/null +++ b/drivers/gpu/drm/drm_vma_manager.c @@ -0,0 +1,224 @@ +/*

• • Copyright (c) 2012 David Airlie airlied@linux.ie
• • Copyright (c) 2013 David Herrmann dh.herrmann@gmail.com
• • Permission is hereby granted, free of charge, to any person obtaining a
• • copy of this software and associated documentation files (the "Software"),
• • to deal in the Software without restriction, including without limitation
• • the rights to use, copy, modify, merge, publish, distribute, sublicense,
• • and/or sell copies of the Software, and to permit persons to whom the
• • Software is furnished to do so, subject to the following conditions:
• • The above copyright notice and this permission notice shall be included in
• • all copies or substantial portions of the Software.
• • THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
• • IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
• • FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
• • THE COPYRIGHT HOLDER(S) OR AUTHOR(S) BE LIABLE FOR ANY CLAIM, DAMAGES OR
• • OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
• • ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
• • OTHER DEALINGS IN THE SOFTWARE.
• */

+#include <drm/drmP.h> +#include <drm/drm_mm.h> +#include <drm/drm_vma_manager.h> +#include <linux/mm.h> +#include <linux/module.h> +#include <linux/rbtree.h> +#include <linux/slab.h> +#include <linux/spinlock.h> +#include <linux/types.h>

+/** @file drm_vma_manager.c

• • The vma-manager is responsible to map arbitrary driver-dependent memory
• • regions into the linear user address-space. It provides offsets to the
• • caller which can then be used on the address_space of the drm-device. It
• • takes care to not overlap regions, size them appropriately and to not
• • confuse mm-core by inconsistent fake vm_pgoff fields.
• • We use drm_mm as backend to manage object allocations. But it is highly
• • optimized for alloc/free calls, not lookups. Hence, we use an rb-tree to
• • speed up offset lookups.
• */

+/** drm_vma_offset_manager_init()

• • Initialize a new offset-manager. The offset and area size available for the
• • manager are given as @page_offset and @size. Both are interpreted as
• • page-numbers, not bytes.
• • Adding/removing nodes from the manager is locked internally and protected
• • against concurrent access. However, node allocation and destruction is left
• • for the caller. While calling into the vma-manager, a given node must
• • always be guaranteed to be referenced.
• */

+void drm_vma_offset_manager_init(struct drm_vma_offset_manager *mgr,

• 		 unsigned long page_offset, unsigned long size)
  

+{

• rwlock_init(&mgr->vm_lock);
• mgr->vm_addr_space_rb = RB_ROOT;
• drm_mm_init(&mgr->vm_addr_space_mm, page_offset, size);

+} +EXPORT_SYMBOL(drm_vma_offset_manager_init);

+/** drm_vma_offset_manager_destroy()

• • Destroy an object manager which was previously created via
• • drm_vma_offset_manager_init(). The caller must remove all allocated nodes
• • before destroying the manager. Otherwise, drm_mm will refuse to free the
• • requested resources.
• • The manager must not be accessed after this function is called.
• */

+void drm_vma_offset_manager_destroy(struct drm_vma_offset_manager *mgr) +{

• BUG_ON(!drm_mm_clean(&mgr->vm_addr_space_mm));

Please convert this to a WARN_ON - drm_mm has code to cobble over buggy drivers, and killing the driver with a BUG_ON if we could keep on going with just a WARN_ON is a real pain for development.

• /* take the lock to protect against buggy drivers */
• write_lock(&mgr->vm_lock);
• drm_mm_takedown(&mgr->vm_addr_space_mm);
• write_unlock(&mgr->vm_lock);

+} +EXPORT_SYMBOL(drm_vma_offset_manager_destroy);

+/** drm_vma_offset_lookup()

• • Find a node given a start address and object size. This returns the _best_
• • match for the given node. That is, @start may point somewhere into a valid
• • region and the given node will be returned, as long as the node spans the
• • whole requested area (given the size in number of pages as @pages).
• • Returns NULL if no suitable node can be found. Otherwise, the best match
• • is returned. It's the caller's responsibility to make sure the node doesn't
• • get destroyed before the caller can access it.
• */

+struct drm_vma_offset_node *drm_vma_offset_lookup(struct drm_vma_offset_manager *mgr,

• 				  unsigned long start,
  

• 				  unsigned long pages)
  

+{

• struct drm_vma_offset_node *node, *best;
• struct rb_node *iter;
• unsigned long offset;
• read_lock(&mgr->vm_lock);
• iter = mgr->vm_addr_space_rb.rb_node;
• best = NULL;
• while (likely(iter)) {

• node = rb_entry(iter, struct drm_vma_offset_node, vm_rb);
  

• offset = node->vm_node.start;
  

• if (start >= offset) {
  

• 	iter = iter->rb_right;
  

• 	best = node;
  

• 	if (start == offset)
  

• 		break;
  

• } else {
  

• 	iter = iter->rb_left;
  

• }
  

• }
• /* verify that the node spans the requested area */
• if (likely(best)) {

• offset = best->vm_node.start + best->vm_pages;
  

• if (offset > start + pages)
  

• 	best = NULL;
  

• }
• read_unlock(&mgr->vm_lock);
• return best;

+} +EXPORT_SYMBOL(drm_vma_offset_lookup);

+/* internal helper to link @node into the rb-tree */ +static void _drm_vma_offset_add_rb(struct drm_vma_offset_manager *mgr,

• 		   struct drm_vma_offset_node *node)
  

+{

• struct rb_node **iter = &mgr->vm_addr_space_rb.rb_node;
• struct rb_node *parent = NULL;
• struct drm_vma_offset_node *iter_node;
• while (likely(*iter)) {

• parent = *iter;
  

• iter_node = rb_entry(*iter, struct drm_vma_offset_node, vm_rb);
  

• if (node->vm_node.start < iter_node->vm_node.start)
  

• 	iter = &(*iter)->rb_left;
  

• else if (node->vm_node.start > iter_node->vm_node.start)
  

• 	iter = &(*iter)->rb_right;
  

• else
  

• 	BUG();
  

• }
• rb_link_node(&node->vm_rb, parent, iter);
• rb_insert_color(&node->vm_rb, &mgr->vm_addr_space_rb);

+}

+/** drm_vma_offset_add()

• • Add a node to the offset-manager. If the node was already added, this does
• • nothing and return 0. @pages is the size of the object given in number of
• • pages.
• • After this call succeeds, you can access the offset of the node until it
• • is removed again.
• • If this call fails, it is safe to retry the operation or call
• • drm_vma_offset_remove(), anyway. However, no cleanup is required in that
• • case.
• */

+int drm_vma_offset_add(struct drm_vma_offset_manager *mgr,

•        struct drm_vma_offset_node *node, unsigned long pages)
  

+{

• int ret;
• write_lock(&mgr->vm_lock);
• if (unlikely(drm_mm_node_linked(&node->vm_node))) {

• ret = 0;
  

• goto out_unlock;
  

• }
• ret = drm_mm_insert_node_generic(&mgr->vm_addr_space_mm,

• 			 &node->vm_node, pages, 0, 0);
  

This allocates memory, so potentially blocks. This doesn't mesh well with the spinning rwlock (lockdep should seriously complain about this btw). Please use an rwsemaphore instead.

• if (unlikely(ret))

• goto out_reset;
  

• node->vm_pages = pages;
• _drm_vma_offset_add_rb(mgr, node);
• goto out_unlock;

+out_reset:

• /* we don't know what happened to @node->vm_node, so clear it */
• drm_vma_node_reset(node);

If you switch over to drm_mm_node_allocated then this reset could shouldn't be required - it'd be a pretty serious bug in drm_mm.c

+out_unlock:

• write_unlock(&mgr->vm_lock);
• return ret;

+} +EXPORT_SYMBOL(drm_vma_offset_add);

+/** drm_vma_offset_remove()

• • Remove a node from the offset manager. If the node wasn't added before, this
• • does nothing. After this call returns, the offset of the node must be not
• • accessed, anymore.
• • It is safe to add the node via drm_vma_offset_add() again.
• */

+void drm_vma_offset_remove(struct drm_vma_offset_manager *mgr,

• 	   struct drm_vma_offset_node *node)
  

+{

• if (unlikely(!drm_mm_node_linked(&node->vm_node)))

• return;
  

• write_lock(&mgr->vm_lock);
• rb_erase(&node->vm_rb, &mgr->vm_addr_space_rb);
• drm_mm_remove_node(&node->vm_node);
• drm_vma_node_reset(node);
• write_unlock(&mgr->vm_lock);

+} +EXPORT_SYMBOL(drm_vma_offset_remove); diff --git a/include/drm/drm_vma_manager.h b/include/drm/drm_vma_manager.h new file mode 100644 index 0000000..8a1975c --- /dev/null +++ b/include/drm/drm_vma_manager.h @@ -0,0 +1,107 @@ +#ifndef __DRM_VMA_MANAGER_H__ +#define __DRM_VMA_MANAGER_H__

+/*

• • Copyright (c) 2013 David Herrmann dh.herrmann@gmail.com
• • Permission is hereby granted, free of charge, to any person obtaining a
• • copy of this software and associated documentation files (the "Software"),
• • to deal in the Software without restriction, including without limitation
• • the rights to use, copy, modify, merge, publish, distribute, sublicense,
• • and/or sell copies of the Software, and to permit persons to whom the
• • Software is furnished to do so, subject to the following conditions:
• • The above copyright notice and this permission notice shall be included in
• • all copies or substantial portions of the Software.
• • THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
• • IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
• • FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
• • THE COPYRIGHT HOLDER(S) OR AUTHOR(S) BE LIABLE FOR ANY CLAIM, DAMAGES OR
• • OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
• • ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
• • OTHER DEALINGS IN THE SOFTWARE.
• */

+#include <drm/drmP.h> +#include <drm/drm_mm.h> +#include <linux/module.h> +#include <linux/rbtree.h> +#include <linux/spinlock.h> +#include <linux/types.h>

+struct drm_vma_offset_node {

• struct drm_mm_node vm_node;
• struct rb_node vm_rb;
• unsigned long vm_pages;

+};

+struct drm_vma_offset_manager {

• rwlock_t vm_lock;
• struct rb_root vm_addr_space_rb;
• struct drm_mm vm_addr_space_mm;

+};

+void drm_vma_offset_manager_init(struct drm_vma_offset_manager *mgr,

• 		 unsigned long page_offset, unsigned long size);
  

+void drm_vma_offset_manager_destroy(struct drm_vma_offset_manager *mgr);

+struct drm_vma_offset_node *drm_vma_offset_lookup(struct drm_vma_offset_manager *mgr,

• 				  unsigned long start,
  

• 				  unsigned long pages);
  

+int drm_vma_offset_add(struct drm_vma_offset_manager *mgr,

•        struct drm_vma_offset_node *node, unsigned long pages);
  

+void drm_vma_offset_remove(struct drm_vma_offset_manager *mgr,

• 	   struct drm_vma_offset_node *node);
  

+/** drm_vma_offset_exact_lookup()

• • Same as drm_vma_offset_lookup() but does not allow any offset but only
• • returns the exact object with the given start address.
• */

+static inline struct drm_vma_offset_node * +drm_vma_offset_exact_lookup(struct drm_vma_offset_manager *mgr,

• 	    unsigned long start)
  

+{

• return drm_vma_offset_lookup(mgr, start, 1);

+}

+/** drm_vma_node_reset()

• • Reset a node to its initial state.
• */

+static inline void drm_vma_node_reset(struct drm_vma_offset_node *node) +{

• memset(&node->vm_node, 0, sizeof(node->vm_node));

+}

+/** drm_vma_node_start()

• • Return the start address of the given node as pfn.
• */

+static inline unsigned long drm_vma_node_start(struct drm_vma_offset_node *node) +{

• return node->vm_node.start;

+}

+/** drm_vma_node_has_offset()

• • Return true iff the node was previously allocated an offset and added to
• • an vma offset manager.
• */

+static inline bool drm_vma_node_has_offset(struct drm_vma_offset_node *node) +{

• return drm_mm_node_linked(&node->vm_node);

+}

+/** drm_vma_node_offset_addr()

• • Same as drm_vma_node_start() but returns the address as a valid userspace
• • address (instead of a pfn).
• */

Userspace address and pfn are a bit misleading imo in this context. I'd go with "byte offset for consumption by userspace/mmap" and "page-based addressing" or something similar.

+static inline __u64 drm_vma_node_offset_addr(struct drm_vma_offset_node *node) +{

• return ((__u64)node->vm_node.start) << PAGE_SHIFT;

+}

+#endif /* __DRM_VMA_MANAGER_H__ */

1.8.3.2

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